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- // SPDX-License-Identifier: GPL-2.0
- #include <linux/kernel.h>
- #include <linux/irqflags.h>
- #include <linux/string.h>
- #include <linux/errno.h>
- #include <linux/bug.h>
- #include "printk_ringbuffer.h"
- /**
- * DOC: printk_ringbuffer overview
- *
- * Data Structure
- * --------------
- * The printk_ringbuffer is made up of 3 internal ringbuffers:
- *
- * desc_ring
- * A ring of descriptors and their meta data (such as sequence number,
- * timestamp, loglevel, etc.) as well as internal state information about
- * the record and logical positions specifying where in the other
- * ringbuffer the text strings are located.
- *
- * text_data_ring
- * A ring of data blocks. A data block consists of an unsigned long
- * integer (ID) that maps to a desc_ring index followed by the text
- * string of the record.
- *
- * The internal state information of a descriptor is the key element to allow
- * readers and writers to locklessly synchronize access to the data.
- *
- * Implementation
- * --------------
- *
- * Descriptor Ring
- * ~~~~~~~~~~~~~~~
- * The descriptor ring is an array of descriptors. A descriptor contains
- * essential meta data to track the data of a printk record using
- * blk_lpos structs pointing to associated text data blocks (see
- * "Data Rings" below). Each descriptor is assigned an ID that maps
- * directly to index values of the descriptor array and has a state. The ID
- * and the state are bitwise combined into a single descriptor field named
- * @state_var, allowing ID and state to be synchronously and atomically
- * updated.
- *
- * Descriptors have four states:
- *
- * reserved
- * A writer is modifying the record.
- *
- * committed
- * The record and all its data are written. A writer can reopen the
- * descriptor (transitioning it back to reserved), but in the committed
- * state the data is consistent.
- *
- * finalized
- * The record and all its data are complete and available for reading. A
- * writer cannot reopen the descriptor.
- *
- * reusable
- * The record exists, but its text and/or meta data may no longer be
- * available.
- *
- * Querying the @state_var of a record requires providing the ID of the
- * descriptor to query. This can yield a possible fifth (pseudo) state:
- *
- * miss
- * The descriptor being queried has an unexpected ID.
- *
- * The descriptor ring has a @tail_id that contains the ID of the oldest
- * descriptor and @head_id that contains the ID of the newest descriptor.
- *
- * When a new descriptor should be created (and the ring is full), the tail
- * descriptor is invalidated by first transitioning to the reusable state and
- * then invalidating all tail data blocks up to and including the data blocks
- * associated with the tail descriptor (for the text ring). Then
- * @tail_id is advanced, followed by advancing @head_id. And finally the
- * @state_var of the new descriptor is initialized to the new ID and reserved
- * state.
- *
- * The @tail_id can only be advanced if the new @tail_id would be in the
- * committed or reusable queried state. This makes it possible that a valid
- * sequence number of the tail is always available.
- *
- * Descriptor Finalization
- * ~~~~~~~~~~~~~~~~~~~~~~~
- * When a writer calls the commit function prb_commit(), record data is
- * fully stored and is consistent within the ringbuffer. However, a writer can
- * reopen that record, claiming exclusive access (as with prb_reserve()), and
- * modify that record. When finished, the writer must again commit the record.
- *
- * In order for a record to be made available to readers (and also become
- * recyclable for writers), it must be finalized. A finalized record cannot be
- * reopened and can never become "unfinalized". Record finalization can occur
- * in three different scenarios:
- *
- * 1) A writer can simultaneously commit and finalize its record by calling
- * prb_final_commit() instead of prb_commit().
- *
- * 2) When a new record is reserved and the previous record has been
- * committed via prb_commit(), that previous record is automatically
- * finalized.
- *
- * 3) When a record is committed via prb_commit() and a newer record
- * already exists, the record being committed is automatically finalized.
- *
- * Data Ring
- * ~~~~~~~~~
- * The text data ring is a byte array composed of data blocks. Data blocks are
- * referenced by blk_lpos structs that point to the logical position of the
- * beginning of a data block and the beginning of the next adjacent data
- * block. Logical positions are mapped directly to index values of the byte
- * array ringbuffer.
- *
- * Each data block consists of an ID followed by the writer data. The ID is
- * the identifier of a descriptor that is associated with the data block. A
- * given data block is considered valid if all of the following conditions
- * are met:
- *
- * 1) The descriptor associated with the data block is in the committed
- * or finalized queried state.
- *
- * 2) The blk_lpos struct within the descriptor associated with the data
- * block references back to the same data block.
- *
- * 3) The data block is within the head/tail logical position range.
- *
- * If the writer data of a data block would extend beyond the end of the
- * byte array, only the ID of the data block is stored at the logical
- * position and the full data block (ID and writer data) is stored at the
- * beginning of the byte array. The referencing blk_lpos will point to the
- * ID before the wrap and the next data block will be at the logical
- * position adjacent the full data block after the wrap.
- *
- * Data rings have a @tail_lpos that points to the beginning of the oldest
- * data block and a @head_lpos that points to the logical position of the
- * next (not yet existing) data block.
- *
- * When a new data block should be created (and the ring is full), tail data
- * blocks will first be invalidated by putting their associated descriptors
- * into the reusable state and then pushing the @tail_lpos forward beyond
- * them. Then the @head_lpos is pushed forward and is associated with a new
- * descriptor. If a data block is not valid, the @tail_lpos cannot be
- * advanced beyond it.
- *
- * Info Array
- * ~~~~~~~~~~
- * The general meta data of printk records are stored in printk_info structs,
- * stored in an array with the same number of elements as the descriptor ring.
- * Each info corresponds to the descriptor of the same index in the
- * descriptor ring. Info validity is confirmed by evaluating the corresponding
- * descriptor before and after loading the info.
- *
- * Usage
- * -----
- * Here are some simple examples demonstrating writers and readers. For the
- * examples a global ringbuffer (test_rb) is available (which is not the
- * actual ringbuffer used by printk)::
- *
- * DEFINE_PRINTKRB(test_rb, 15, 5);
- *
- * This ringbuffer allows up to 32768 records (2 ^ 15) and has a size of
- * 1 MiB (2 ^ (15 + 5)) for text data.
- *
- * Sample writer code::
- *
- * const char *textstr = "message text";
- * struct prb_reserved_entry e;
- * struct printk_record r;
- *
- * // specify how much to allocate
- * prb_rec_init_wr(&r, strlen(textstr) + 1);
- *
- * if (prb_reserve(&e, &test_rb, &r)) {
- * snprintf(r.text_buf, r.text_buf_size, "%s", textstr);
- *
- * r.info->text_len = strlen(textstr);
- * r.info->ts_nsec = local_clock();
- * r.info->caller_id = printk_caller_id();
- *
- * // commit and finalize the record
- * prb_final_commit(&e);
- * }
- *
- * Note that additional writer functions are available to extend a record
- * after it has been committed but not yet finalized. This can be done as
- * long as no new records have been reserved and the caller is the same.
- *
- * Sample writer code (record extending)::
- *
- * // alternate rest of previous example
- *
- * r.info->text_len = strlen(textstr);
- * r.info->ts_nsec = local_clock();
- * r.info->caller_id = printk_caller_id();
- *
- * // commit the record (but do not finalize yet)
- * prb_commit(&e);
- * }
- *
- * ...
- *
- * // specify additional 5 bytes text space to extend
- * prb_rec_init_wr(&r, 5);
- *
- * // try to extend, but only if it does not exceed 32 bytes
- * if (prb_reserve_in_last(&e, &test_rb, &r, printk_caller_id()), 32) {
- * snprintf(&r.text_buf[r.info->text_len],
- * r.text_buf_size - r.info->text_len, "hello");
- *
- * r.info->text_len += 5;
- *
- * // commit and finalize the record
- * prb_final_commit(&e);
- * }
- *
- * Sample reader code::
- *
- * struct printk_info info;
- * struct printk_record r;
- * char text_buf[32];
- * u64 seq;
- *
- * prb_rec_init_rd(&r, &info, &text_buf[0], sizeof(text_buf));
- *
- * prb_for_each_record(0, &test_rb, &seq, &r) {
- * if (info.seq != seq)
- * pr_warn("lost %llu records\n", info.seq - seq);
- *
- * if (info.text_len > r.text_buf_size) {
- * pr_warn("record %llu text truncated\n", info.seq);
- * text_buf[r.text_buf_size - 1] = 0;
- * }
- *
- * pr_info("%llu: %llu: %s\n", info.seq, info.ts_nsec,
- * &text_buf[0]);
- * }
- *
- * Note that additional less convenient reader functions are available to
- * allow complex record access.
- *
- * ABA Issues
- * ~~~~~~~~~~
- * To help avoid ABA issues, descriptors are referenced by IDs (array index
- * values combined with tagged bits counting array wraps) and data blocks are
- * referenced by logical positions (array index values combined with tagged
- * bits counting array wraps). However, on 32-bit systems the number of
- * tagged bits is relatively small such that an ABA incident is (at least
- * theoretically) possible. For example, if 4 million maximally sized (1KiB)
- * printk messages were to occur in NMI context on a 32-bit system, the
- * interrupted context would not be able to recognize that the 32-bit integer
- * completely wrapped and thus represents a different data block than the one
- * the interrupted context expects.
- *
- * To help combat this possibility, additional state checking is performed
- * (such as using cmpxchg() even though set() would suffice). These extra
- * checks are commented as such and will hopefully catch any ABA issue that
- * a 32-bit system might experience.
- *
- * Memory Barriers
- * ~~~~~~~~~~~~~~~
- * Multiple memory barriers are used. To simplify proving correctness and
- * generating litmus tests, lines of code related to memory barriers
- * (loads, stores, and the associated memory barriers) are labeled::
- *
- * LMM(function:letter)
- *
- * Comments reference the labels using only the "function:letter" part.
- *
- * The memory barrier pairs and their ordering are:
- *
- * desc_reserve:D / desc_reserve:B
- * push descriptor tail (id), then push descriptor head (id)
- *
- * desc_reserve:D / data_push_tail:B
- * push data tail (lpos), then set new descriptor reserved (state)
- *
- * desc_reserve:D / desc_push_tail:C
- * push descriptor tail (id), then set new descriptor reserved (state)
- *
- * desc_reserve:D / prb_first_seq:C
- * push descriptor tail (id), then set new descriptor reserved (state)
- *
- * desc_reserve:F / desc_read:D
- * set new descriptor id and reserved (state), then allow writer changes
- *
- * data_alloc:A (or data_realloc:A) / desc_read:D
- * set old descriptor reusable (state), then modify new data block area
- *
- * data_alloc:A (or data_realloc:A) / data_push_tail:B
- * push data tail (lpos), then modify new data block area
- *
- * _prb_commit:B / desc_read:B
- * store writer changes, then set new descriptor committed (state)
- *
- * desc_reopen_last:A / _prb_commit:B
- * set descriptor reserved (state), then read descriptor data
- *
- * _prb_commit:B / desc_reserve:D
- * set new descriptor committed (state), then check descriptor head (id)
- *
- * data_push_tail:D / data_push_tail:A
- * set descriptor reusable (state), then push data tail (lpos)
- *
- * desc_push_tail:B / desc_reserve:D
- * set descriptor reusable (state), then push descriptor tail (id)
- */
- #define DATA_SIZE(data_ring) _DATA_SIZE((data_ring)->size_bits)
- #define DATA_SIZE_MASK(data_ring) (DATA_SIZE(data_ring) - 1)
- #define DESCS_COUNT(desc_ring) _DESCS_COUNT((desc_ring)->count_bits)
- #define DESCS_COUNT_MASK(desc_ring) (DESCS_COUNT(desc_ring) - 1)
- /* Determine the data array index from a logical position. */
- #define DATA_INDEX(data_ring, lpos) ((lpos) & DATA_SIZE_MASK(data_ring))
- /* Determine the desc array index from an ID or sequence number. */
- #define DESC_INDEX(desc_ring, n) ((n) & DESCS_COUNT_MASK(desc_ring))
- /* Determine how many times the data array has wrapped. */
- #define DATA_WRAPS(data_ring, lpos) ((lpos) >> (data_ring)->size_bits)
- /* Determine if a logical position refers to a data-less block. */
- #define LPOS_DATALESS(lpos) ((lpos) & 1UL)
- #define BLK_DATALESS(blk) (LPOS_DATALESS((blk)->begin) && \
- LPOS_DATALESS((blk)->next))
- /* Get the logical position at index 0 of the current wrap. */
- #define DATA_THIS_WRAP_START_LPOS(data_ring, lpos) \
- ((lpos) & ~DATA_SIZE_MASK(data_ring))
- /* Get the ID for the same index of the previous wrap as the given ID. */
- #define DESC_ID_PREV_WRAP(desc_ring, id) \
- DESC_ID((id) - DESCS_COUNT(desc_ring))
- /*
- * A data block: mapped directly to the beginning of the data block area
- * specified as a logical position within the data ring.
- *
- * @id: the ID of the associated descriptor
- * @data: the writer data
- *
- * Note that the size of a data block is only known by its associated
- * descriptor.
- */
- struct prb_data_block {
- unsigned long id;
- char data[];
- };
- /*
- * Return the descriptor associated with @n. @n can be either a
- * descriptor ID or a sequence number.
- */
- static struct prb_desc *to_desc(struct prb_desc_ring *desc_ring, u64 n)
- {
- return &desc_ring->descs[DESC_INDEX(desc_ring, n)];
- }
- /*
- * Return the printk_info associated with @n. @n can be either a
- * descriptor ID or a sequence number.
- */
- static struct printk_info *to_info(struct prb_desc_ring *desc_ring, u64 n)
- {
- return &desc_ring->infos[DESC_INDEX(desc_ring, n)];
- }
- static struct prb_data_block *to_block(struct prb_data_ring *data_ring,
- unsigned long begin_lpos)
- {
- return (void *)&data_ring->data[DATA_INDEX(data_ring, begin_lpos)];
- }
- /*
- * Increase the data size to account for data block meta data plus any
- * padding so that the adjacent data block is aligned on the ID size.
- */
- static unsigned int to_blk_size(unsigned int size)
- {
- struct prb_data_block *db = NULL;
- size += sizeof(*db);
- size = ALIGN(size, sizeof(db->id));
- return size;
- }
- /*
- * Sanity checker for reserve size. The ringbuffer code assumes that a data
- * block does not exceed the maximum possible size that could fit within the
- * ringbuffer. This function provides that basic size check so that the
- * assumption is safe.
- */
- static bool data_check_size(struct prb_data_ring *data_ring, unsigned int size)
- {
- struct prb_data_block *db = NULL;
- if (size == 0)
- return true;
- /*
- * Ensure the alignment padded size could possibly fit in the data
- * array. The largest possible data block must still leave room for
- * at least the ID of the next block.
- */
- size = to_blk_size(size);
- if (size > DATA_SIZE(data_ring) - sizeof(db->id))
- return false;
- return true;
- }
- /* Query the state of a descriptor. */
- static enum desc_state get_desc_state(unsigned long id,
- unsigned long state_val)
- {
- if (id != DESC_ID(state_val))
- return desc_miss;
- return DESC_STATE(state_val);
- }
- /*
- * Get a copy of a specified descriptor and return its queried state. If the
- * descriptor is in an inconsistent state (miss or reserved), the caller can
- * only expect the descriptor's @state_var field to be valid.
- *
- * The sequence number and caller_id can be optionally retrieved. Like all
- * non-state_var data, they are only valid if the descriptor is in a
- * consistent state.
- */
- static enum desc_state desc_read(struct prb_desc_ring *desc_ring,
- unsigned long id, struct prb_desc *desc_out,
- u64 *seq_out, u32 *caller_id_out)
- {
- struct printk_info *info = to_info(desc_ring, id);
- struct prb_desc *desc = to_desc(desc_ring, id);
- atomic_long_t *state_var = &desc->state_var;
- enum desc_state d_state;
- unsigned long state_val;
- /* Check the descriptor state. */
- state_val = atomic_long_read(state_var); /* LMM(desc_read:A) */
- d_state = get_desc_state(id, state_val);
- if (d_state == desc_miss || d_state == desc_reserved) {
- /*
- * The descriptor is in an inconsistent state. Set at least
- * @state_var so that the caller can see the details of
- * the inconsistent state.
- */
- goto out;
- }
- /*
- * Guarantee the state is loaded before copying the descriptor
- * content. This avoids copying obsolete descriptor content that might
- * not apply to the descriptor state. This pairs with _prb_commit:B.
- *
- * Memory barrier involvement:
- *
- * If desc_read:A reads from _prb_commit:B, then desc_read:C reads
- * from _prb_commit:A.
- *
- * Relies on:
- *
- * WMB from _prb_commit:A to _prb_commit:B
- * matching
- * RMB from desc_read:A to desc_read:C
- */
- smp_rmb(); /* LMM(desc_read:B) */
- /*
- * Copy the descriptor data. The data is not valid until the
- * state has been re-checked. A memcpy() for all of @desc
- * cannot be used because of the atomic_t @state_var field.
- */
- if (desc_out) {
- memcpy(&desc_out->text_blk_lpos, &desc->text_blk_lpos,
- sizeof(desc_out->text_blk_lpos)); /* LMM(desc_read:C) */
- }
- if (seq_out)
- *seq_out = info->seq; /* also part of desc_read:C */
- if (caller_id_out)
- *caller_id_out = info->caller_id; /* also part of desc_read:C */
- /*
- * 1. Guarantee the descriptor content is loaded before re-checking
- * the state. This avoids reading an obsolete descriptor state
- * that may not apply to the copied content. This pairs with
- * desc_reserve:F.
- *
- * Memory barrier involvement:
- *
- * If desc_read:C reads from desc_reserve:G, then desc_read:E
- * reads from desc_reserve:F.
- *
- * Relies on:
- *
- * WMB from desc_reserve:F to desc_reserve:G
- * matching
- * RMB from desc_read:C to desc_read:E
- *
- * 2. Guarantee the record data is loaded before re-checking the
- * state. This avoids reading an obsolete descriptor state that may
- * not apply to the copied data. This pairs with data_alloc:A and
- * data_realloc:A.
- *
- * Memory barrier involvement:
- *
- * If copy_data:A reads from data_alloc:B, then desc_read:E
- * reads from desc_make_reusable:A.
- *
- * Relies on:
- *
- * MB from desc_make_reusable:A to data_alloc:B
- * matching
- * RMB from desc_read:C to desc_read:E
- *
- * Note: desc_make_reusable:A and data_alloc:B can be different
- * CPUs. However, the data_alloc:B CPU (which performs the
- * full memory barrier) must have previously seen
- * desc_make_reusable:A.
- */
- smp_rmb(); /* LMM(desc_read:D) */
- /*
- * The data has been copied. Return the current descriptor state,
- * which may have changed since the load above.
- */
- state_val = atomic_long_read(state_var); /* LMM(desc_read:E) */
- d_state = get_desc_state(id, state_val);
- out:
- if (desc_out)
- atomic_long_set(&desc_out->state_var, state_val);
- return d_state;
- }
- /*
- * Take a specified descriptor out of the finalized state by attempting
- * the transition from finalized to reusable. Either this context or some
- * other context will have been successful.
- */
- static void desc_make_reusable(struct prb_desc_ring *desc_ring,
- unsigned long id)
- {
- unsigned long val_finalized = DESC_SV(id, desc_finalized);
- unsigned long val_reusable = DESC_SV(id, desc_reusable);
- struct prb_desc *desc = to_desc(desc_ring, id);
- atomic_long_t *state_var = &desc->state_var;
- atomic_long_cmpxchg_relaxed(state_var, val_finalized,
- val_reusable); /* LMM(desc_make_reusable:A) */
- }
- /*
- * Given the text data ring, put the associated descriptor of each
- * data block from @lpos_begin until @lpos_end into the reusable state.
- *
- * If there is any problem making the associated descriptor reusable, either
- * the descriptor has not yet been finalized or another writer context has
- * already pushed the tail lpos past the problematic data block. Regardless,
- * on error the caller can re-load the tail lpos to determine the situation.
- */
- static bool data_make_reusable(struct printk_ringbuffer *rb,
- struct prb_data_ring *data_ring,
- unsigned long lpos_begin,
- unsigned long lpos_end,
- unsigned long *lpos_out)
- {
- struct prb_desc_ring *desc_ring = &rb->desc_ring;
- struct prb_data_block *blk;
- enum desc_state d_state;
- struct prb_desc desc;
- struct prb_data_blk_lpos *blk_lpos = &desc.text_blk_lpos;
- unsigned long id;
- /* Loop until @lpos_begin has advanced to or beyond @lpos_end. */
- while ((lpos_end - lpos_begin) - 1 < DATA_SIZE(data_ring)) {
- blk = to_block(data_ring, lpos_begin);
- /*
- * Load the block ID from the data block. This is a data race
- * against a writer that may have newly reserved this data
- * area. If the loaded value matches a valid descriptor ID,
- * the blk_lpos of that descriptor will be checked to make
- * sure it points back to this data block. If the check fails,
- * the data area has been recycled by another writer.
- */
- id = blk->id; /* LMM(data_make_reusable:A) */
- d_state = desc_read(desc_ring, id, &desc,
- NULL, NULL); /* LMM(data_make_reusable:B) */
- switch (d_state) {
- case desc_miss:
- case desc_reserved:
- case desc_committed:
- return false;
- case desc_finalized:
- /*
- * This data block is invalid if the descriptor
- * does not point back to it.
- */
- if (blk_lpos->begin != lpos_begin)
- return false;
- desc_make_reusable(desc_ring, id);
- break;
- case desc_reusable:
- /*
- * This data block is invalid if the descriptor
- * does not point back to it.
- */
- if (blk_lpos->begin != lpos_begin)
- return false;
- break;
- }
- /* Advance @lpos_begin to the next data block. */
- lpos_begin = blk_lpos->next;
- }
- *lpos_out = lpos_begin;
- return true;
- }
- /*
- * Advance the data ring tail to at least @lpos. This function puts
- * descriptors into the reusable state if the tail is pushed beyond
- * their associated data block.
- */
- static bool data_push_tail(struct printk_ringbuffer *rb,
- struct prb_data_ring *data_ring,
- unsigned long lpos)
- {
- unsigned long tail_lpos_new;
- unsigned long tail_lpos;
- unsigned long next_lpos;
- /* If @lpos is from a data-less block, there is nothing to do. */
- if (LPOS_DATALESS(lpos))
- return true;
- /*
- * Any descriptor states that have transitioned to reusable due to the
- * data tail being pushed to this loaded value will be visible to this
- * CPU. This pairs with data_push_tail:D.
- *
- * Memory barrier involvement:
- *
- * If data_push_tail:A reads from data_push_tail:D, then this CPU can
- * see desc_make_reusable:A.
- *
- * Relies on:
- *
- * MB from desc_make_reusable:A to data_push_tail:D
- * matches
- * READFROM from data_push_tail:D to data_push_tail:A
- * thus
- * READFROM from desc_make_reusable:A to this CPU
- */
- tail_lpos = atomic_long_read(&data_ring->tail_lpos); /* LMM(data_push_tail:A) */
- /*
- * Loop until the tail lpos is at or beyond @lpos. This condition
- * may already be satisfied, resulting in no full memory barrier
- * from data_push_tail:D being performed. However, since this CPU
- * sees the new tail lpos, any descriptor states that transitioned to
- * the reusable state must already be visible.
- */
- while ((lpos - tail_lpos) - 1 < DATA_SIZE(data_ring)) {
- /*
- * Make all descriptors reusable that are associated with
- * data blocks before @lpos.
- */
- if (!data_make_reusable(rb, data_ring, tail_lpos, lpos,
- &next_lpos)) {
- /*
- * 1. Guarantee the block ID loaded in
- * data_make_reusable() is performed before
- * reloading the tail lpos. The failed
- * data_make_reusable() may be due to a newly
- * recycled data area causing the tail lpos to
- * have been previously pushed. This pairs with
- * data_alloc:A and data_realloc:A.
- *
- * Memory barrier involvement:
- *
- * If data_make_reusable:A reads from data_alloc:B,
- * then data_push_tail:C reads from
- * data_push_tail:D.
- *
- * Relies on:
- *
- * MB from data_push_tail:D to data_alloc:B
- * matching
- * RMB from data_make_reusable:A to
- * data_push_tail:C
- *
- * Note: data_push_tail:D and data_alloc:B can be
- * different CPUs. However, the data_alloc:B
- * CPU (which performs the full memory
- * barrier) must have previously seen
- * data_push_tail:D.
- *
- * 2. Guarantee the descriptor state loaded in
- * data_make_reusable() is performed before
- * reloading the tail lpos. The failed
- * data_make_reusable() may be due to a newly
- * recycled descriptor causing the tail lpos to
- * have been previously pushed. This pairs with
- * desc_reserve:D.
- *
- * Memory barrier involvement:
- *
- * If data_make_reusable:B reads from
- * desc_reserve:F, then data_push_tail:C reads
- * from data_push_tail:D.
- *
- * Relies on:
- *
- * MB from data_push_tail:D to desc_reserve:F
- * matching
- * RMB from data_make_reusable:B to
- * data_push_tail:C
- *
- * Note: data_push_tail:D and desc_reserve:F can
- * be different CPUs. However, the
- * desc_reserve:F CPU (which performs the
- * full memory barrier) must have previously
- * seen data_push_tail:D.
- */
- smp_rmb(); /* LMM(data_push_tail:B) */
- tail_lpos_new = atomic_long_read(&data_ring->tail_lpos
- ); /* LMM(data_push_tail:C) */
- if (tail_lpos_new == tail_lpos)
- return false;
- /* Another CPU pushed the tail. Try again. */
- tail_lpos = tail_lpos_new;
- continue;
- }
- /*
- * Guarantee any descriptor states that have transitioned to
- * reusable are stored before pushing the tail lpos. A full
- * memory barrier is needed since other CPUs may have made
- * the descriptor states reusable. This pairs with
- * data_push_tail:A.
- */
- if (atomic_long_try_cmpxchg(&data_ring->tail_lpos, &tail_lpos,
- next_lpos)) { /* LMM(data_push_tail:D) */
- break;
- }
- }
- return true;
- }
- /*
- * Advance the desc ring tail. This function advances the tail by one
- * descriptor, thus invalidating the oldest descriptor. Before advancing
- * the tail, the tail descriptor is made reusable and all data blocks up to
- * and including the descriptor's data block are invalidated (i.e. the data
- * ring tail is pushed past the data block of the descriptor being made
- * reusable).
- */
- static bool desc_push_tail(struct printk_ringbuffer *rb,
- unsigned long tail_id)
- {
- struct prb_desc_ring *desc_ring = &rb->desc_ring;
- enum desc_state d_state;
- struct prb_desc desc;
- d_state = desc_read(desc_ring, tail_id, &desc, NULL, NULL);
- switch (d_state) {
- case desc_miss:
- /*
- * If the ID is exactly 1 wrap behind the expected, it is
- * in the process of being reserved by another writer and
- * must be considered reserved.
- */
- if (DESC_ID(atomic_long_read(&desc.state_var)) ==
- DESC_ID_PREV_WRAP(desc_ring, tail_id)) {
- return false;
- }
- /*
- * The ID has changed. Another writer must have pushed the
- * tail and recycled the descriptor already. Success is
- * returned because the caller is only interested in the
- * specified tail being pushed, which it was.
- */
- return true;
- case desc_reserved:
- case desc_committed:
- return false;
- case desc_finalized:
- desc_make_reusable(desc_ring, tail_id);
- break;
- case desc_reusable:
- break;
- }
- /*
- * Data blocks must be invalidated before their associated
- * descriptor can be made available for recycling. Invalidating
- * them later is not possible because there is no way to trust
- * data blocks once their associated descriptor is gone.
- */
- if (!data_push_tail(rb, &rb->text_data_ring, desc.text_blk_lpos.next))
- return false;
- /*
- * Check the next descriptor after @tail_id before pushing the tail
- * to it because the tail must always be in a finalized or reusable
- * state. The implementation of prb_first_seq() relies on this.
- *
- * A successful read implies that the next descriptor is less than or
- * equal to @head_id so there is no risk of pushing the tail past the
- * head.
- */
- d_state = desc_read(desc_ring, DESC_ID(tail_id + 1), &desc,
- NULL, NULL); /* LMM(desc_push_tail:A) */
- if (d_state == desc_finalized || d_state == desc_reusable) {
- /*
- * Guarantee any descriptor states that have transitioned to
- * reusable are stored before pushing the tail ID. This allows
- * verifying the recycled descriptor state. A full memory
- * barrier is needed since other CPUs may have made the
- * descriptor states reusable. This pairs with desc_reserve:D.
- */
- atomic_long_cmpxchg(&desc_ring->tail_id, tail_id,
- DESC_ID(tail_id + 1)); /* LMM(desc_push_tail:B) */
- } else {
- /*
- * Guarantee the last state load from desc_read() is before
- * reloading @tail_id in order to see a new tail ID in the
- * case that the descriptor has been recycled. This pairs
- * with desc_reserve:D.
- *
- * Memory barrier involvement:
- *
- * If desc_push_tail:A reads from desc_reserve:F, then
- * desc_push_tail:D reads from desc_push_tail:B.
- *
- * Relies on:
- *
- * MB from desc_push_tail:B to desc_reserve:F
- * matching
- * RMB from desc_push_tail:A to desc_push_tail:D
- *
- * Note: desc_push_tail:B and desc_reserve:F can be different
- * CPUs. However, the desc_reserve:F CPU (which performs
- * the full memory barrier) must have previously seen
- * desc_push_tail:B.
- */
- smp_rmb(); /* LMM(desc_push_tail:C) */
- /*
- * Re-check the tail ID. The descriptor following @tail_id is
- * not in an allowed tail state. But if the tail has since
- * been moved by another CPU, then it does not matter.
- */
- if (atomic_long_read(&desc_ring->tail_id) == tail_id) /* LMM(desc_push_tail:D) */
- return false;
- }
- return true;
- }
- /* Reserve a new descriptor, invalidating the oldest if necessary. */
- static bool desc_reserve(struct printk_ringbuffer *rb, unsigned long *id_out)
- {
- struct prb_desc_ring *desc_ring = &rb->desc_ring;
- unsigned long prev_state_val;
- unsigned long id_prev_wrap;
- struct prb_desc *desc;
- unsigned long head_id;
- unsigned long id;
- head_id = atomic_long_read(&desc_ring->head_id); /* LMM(desc_reserve:A) */
- do {
- id = DESC_ID(head_id + 1);
- id_prev_wrap = DESC_ID_PREV_WRAP(desc_ring, id);
- /*
- * Guarantee the head ID is read before reading the tail ID.
- * Since the tail ID is updated before the head ID, this
- * guarantees that @id_prev_wrap is never ahead of the tail
- * ID. This pairs with desc_reserve:D.
- *
- * Memory barrier involvement:
- *
- * If desc_reserve:A reads from desc_reserve:D, then
- * desc_reserve:C reads from desc_push_tail:B.
- *
- * Relies on:
- *
- * MB from desc_push_tail:B to desc_reserve:D
- * matching
- * RMB from desc_reserve:A to desc_reserve:C
- *
- * Note: desc_push_tail:B and desc_reserve:D can be different
- * CPUs. However, the desc_reserve:D CPU (which performs
- * the full memory barrier) must have previously seen
- * desc_push_tail:B.
- */
- smp_rmb(); /* LMM(desc_reserve:B) */
- if (id_prev_wrap == atomic_long_read(&desc_ring->tail_id
- )) { /* LMM(desc_reserve:C) */
- /*
- * Make space for the new descriptor by
- * advancing the tail.
- */
- if (!desc_push_tail(rb, id_prev_wrap))
- return false;
- }
- /*
- * 1. Guarantee the tail ID is read before validating the
- * recycled descriptor state. A read memory barrier is
- * sufficient for this. This pairs with desc_push_tail:B.
- *
- * Memory barrier involvement:
- *
- * If desc_reserve:C reads from desc_push_tail:B, then
- * desc_reserve:E reads from desc_make_reusable:A.
- *
- * Relies on:
- *
- * MB from desc_make_reusable:A to desc_push_tail:B
- * matching
- * RMB from desc_reserve:C to desc_reserve:E
- *
- * Note: desc_make_reusable:A and desc_push_tail:B can be
- * different CPUs. However, the desc_push_tail:B CPU
- * (which performs the full memory barrier) must have
- * previously seen desc_make_reusable:A.
- *
- * 2. Guarantee the tail ID is stored before storing the head
- * ID. This pairs with desc_reserve:B.
- *
- * 3. Guarantee any data ring tail changes are stored before
- * recycling the descriptor. Data ring tail changes can
- * happen via desc_push_tail()->data_push_tail(). A full
- * memory barrier is needed since another CPU may have
- * pushed the data ring tails. This pairs with
- * data_push_tail:B.
- *
- * 4. Guarantee a new tail ID is stored before recycling the
- * descriptor. A full memory barrier is needed since
- * another CPU may have pushed the tail ID. This pairs
- * with desc_push_tail:C and this also pairs with
- * prb_first_seq:C.
- *
- * 5. Guarantee the head ID is stored before trying to
- * finalize the previous descriptor. This pairs with
- * _prb_commit:B.
- */
- } while (!atomic_long_try_cmpxchg(&desc_ring->head_id, &head_id,
- id)); /* LMM(desc_reserve:D) */
- desc = to_desc(desc_ring, id);
- /*
- * If the descriptor has been recycled, verify the old state val.
- * See "ABA Issues" about why this verification is performed.
- */
- prev_state_val = atomic_long_read(&desc->state_var); /* LMM(desc_reserve:E) */
- if (prev_state_val &&
- get_desc_state(id_prev_wrap, prev_state_val) != desc_reusable) {
- WARN_ON_ONCE(1);
- return false;
- }
- /*
- * Assign the descriptor a new ID and set its state to reserved.
- * See "ABA Issues" about why cmpxchg() instead of set() is used.
- *
- * Guarantee the new descriptor ID and state is stored before making
- * any other changes. A write memory barrier is sufficient for this.
- * This pairs with desc_read:D.
- */
- if (!atomic_long_try_cmpxchg(&desc->state_var, &prev_state_val,
- DESC_SV(id, desc_reserved))) { /* LMM(desc_reserve:F) */
- WARN_ON_ONCE(1);
- return false;
- }
- /* Now data in @desc can be modified: LMM(desc_reserve:G) */
- *id_out = id;
- return true;
- }
- /* Determine the end of a data block. */
- static unsigned long get_next_lpos(struct prb_data_ring *data_ring,
- unsigned long lpos, unsigned int size)
- {
- unsigned long begin_lpos;
- unsigned long next_lpos;
- begin_lpos = lpos;
- next_lpos = lpos + size;
- /* First check if the data block does not wrap. */
- if (DATA_WRAPS(data_ring, begin_lpos) == DATA_WRAPS(data_ring, next_lpos))
- return next_lpos;
- /* Wrapping data blocks store their data at the beginning. */
- return (DATA_THIS_WRAP_START_LPOS(data_ring, next_lpos) + size);
- }
- /*
- * Allocate a new data block, invalidating the oldest data block(s)
- * if necessary. This function also associates the data block with
- * a specified descriptor.
- */
- static char *data_alloc(struct printk_ringbuffer *rb,
- struct prb_data_ring *data_ring, unsigned int size,
- struct prb_data_blk_lpos *blk_lpos, unsigned long id)
- {
- struct prb_data_block *blk;
- unsigned long begin_lpos;
- unsigned long next_lpos;
- if (size == 0) {
- /* Specify a data-less block. */
- blk_lpos->begin = NO_LPOS;
- blk_lpos->next = NO_LPOS;
- return NULL;
- }
- size = to_blk_size(size);
- begin_lpos = atomic_long_read(&data_ring->head_lpos);
- do {
- next_lpos = get_next_lpos(data_ring, begin_lpos, size);
- if (!data_push_tail(rb, data_ring, next_lpos - DATA_SIZE(data_ring))) {
- /* Failed to allocate, specify a data-less block. */
- blk_lpos->begin = FAILED_LPOS;
- blk_lpos->next = FAILED_LPOS;
- return NULL;
- }
- /*
- * 1. Guarantee any descriptor states that have transitioned
- * to reusable are stored before modifying the newly
- * allocated data area. A full memory barrier is needed
- * since other CPUs may have made the descriptor states
- * reusable. See data_push_tail:A about why the reusable
- * states are visible. This pairs with desc_read:D.
- *
- * 2. Guarantee any updated tail lpos is stored before
- * modifying the newly allocated data area. Another CPU may
- * be in data_make_reusable() and is reading a block ID
- * from this area. data_make_reusable() can handle reading
- * a garbage block ID value, but then it must be able to
- * load a new tail lpos. A full memory barrier is needed
- * since other CPUs may have updated the tail lpos. This
- * pairs with data_push_tail:B.
- */
- } while (!atomic_long_try_cmpxchg(&data_ring->head_lpos, &begin_lpos,
- next_lpos)); /* LMM(data_alloc:A) */
- blk = to_block(data_ring, begin_lpos);
- blk->id = id; /* LMM(data_alloc:B) */
- if (DATA_WRAPS(data_ring, begin_lpos) != DATA_WRAPS(data_ring, next_lpos)) {
- /* Wrapping data blocks store their data at the beginning. */
- blk = to_block(data_ring, 0);
- /*
- * Store the ID on the wrapped block for consistency.
- * The printk_ringbuffer does not actually use it.
- */
- blk->id = id;
- }
- blk_lpos->begin = begin_lpos;
- blk_lpos->next = next_lpos;
- return &blk->data[0];
- }
- /*
- * Try to resize an existing data block associated with the descriptor
- * specified by @id. If the resized data block should become wrapped, it
- * copies the old data to the new data block. If @size yields a data block
- * with the same or less size, the data block is left as is.
- *
- * Fail if this is not the last allocated data block or if there is not
- * enough space or it is not possible make enough space.
- *
- * Return a pointer to the beginning of the entire data buffer or NULL on
- * failure.
- */
- static char *data_realloc(struct printk_ringbuffer *rb,
- struct prb_data_ring *data_ring, unsigned int size,
- struct prb_data_blk_lpos *blk_lpos, unsigned long id)
- {
- struct prb_data_block *blk;
- unsigned long head_lpos;
- unsigned long next_lpos;
- bool wrapped;
- /* Reallocation only works if @blk_lpos is the newest data block. */
- head_lpos = atomic_long_read(&data_ring->head_lpos);
- if (head_lpos != blk_lpos->next)
- return NULL;
- /* Keep track if @blk_lpos was a wrapping data block. */
- wrapped = (DATA_WRAPS(data_ring, blk_lpos->begin) != DATA_WRAPS(data_ring, blk_lpos->next));
- size = to_blk_size(size);
- next_lpos = get_next_lpos(data_ring, blk_lpos->begin, size);
- /* If the data block does not increase, there is nothing to do. */
- if (head_lpos - next_lpos < DATA_SIZE(data_ring)) {
- if (wrapped)
- blk = to_block(data_ring, 0);
- else
- blk = to_block(data_ring, blk_lpos->begin);
- return &blk->data[0];
- }
- if (!data_push_tail(rb, data_ring, next_lpos - DATA_SIZE(data_ring)))
- return NULL;
- /* The memory barrier involvement is the same as data_alloc:A. */
- if (!atomic_long_try_cmpxchg(&data_ring->head_lpos, &head_lpos,
- next_lpos)) { /* LMM(data_realloc:A) */
- return NULL;
- }
- blk = to_block(data_ring, blk_lpos->begin);
- if (DATA_WRAPS(data_ring, blk_lpos->begin) != DATA_WRAPS(data_ring, next_lpos)) {
- struct prb_data_block *old_blk = blk;
- /* Wrapping data blocks store their data at the beginning. */
- blk = to_block(data_ring, 0);
- /*
- * Store the ID on the wrapped block for consistency.
- * The printk_ringbuffer does not actually use it.
- */
- blk->id = id;
- if (!wrapped) {
- /*
- * Since the allocated space is now in the newly
- * created wrapping data block, copy the content
- * from the old data block.
- */
- memcpy(&blk->data[0], &old_blk->data[0],
- (blk_lpos->next - blk_lpos->begin) - sizeof(blk->id));
- }
- }
- blk_lpos->next = next_lpos;
- return &blk->data[0];
- }
- /* Return the number of bytes used by a data block. */
- static unsigned int space_used(struct prb_data_ring *data_ring,
- struct prb_data_blk_lpos *blk_lpos)
- {
- /* Data-less blocks take no space. */
- if (BLK_DATALESS(blk_lpos))
- return 0;
- if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next)) {
- /* Data block does not wrap. */
- return (DATA_INDEX(data_ring, blk_lpos->next) -
- DATA_INDEX(data_ring, blk_lpos->begin));
- }
- /*
- * For wrapping data blocks, the trailing (wasted) space is
- * also counted.
- */
- return (DATA_INDEX(data_ring, blk_lpos->next) +
- DATA_SIZE(data_ring) - DATA_INDEX(data_ring, blk_lpos->begin));
- }
- /*
- * Given @blk_lpos, return a pointer to the writer data from the data block
- * and calculate the size of the data part. A NULL pointer is returned if
- * @blk_lpos specifies values that could never be legal.
- *
- * This function (used by readers) performs strict validation on the lpos
- * values to possibly detect bugs in the writer code. A WARN_ON_ONCE() is
- * triggered if an internal error is detected.
- */
- static const char *get_data(struct prb_data_ring *data_ring,
- struct prb_data_blk_lpos *blk_lpos,
- unsigned int *data_size)
- {
- struct prb_data_block *db;
- /* Data-less data block description. */
- if (BLK_DATALESS(blk_lpos)) {
- if (blk_lpos->begin == NO_LPOS && blk_lpos->next == NO_LPOS) {
- *data_size = 0;
- return "";
- }
- return NULL;
- }
- /* Regular data block: @begin less than @next and in same wrap. */
- if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next) &&
- blk_lpos->begin < blk_lpos->next) {
- db = to_block(data_ring, blk_lpos->begin);
- *data_size = blk_lpos->next - blk_lpos->begin;
- /* Wrapping data block: @begin is one wrap behind @next. */
- } else if (DATA_WRAPS(data_ring, blk_lpos->begin + DATA_SIZE(data_ring)) ==
- DATA_WRAPS(data_ring, blk_lpos->next)) {
- db = to_block(data_ring, 0);
- *data_size = DATA_INDEX(data_ring, blk_lpos->next);
- /* Illegal block description. */
- } else {
- WARN_ON_ONCE(1);
- return NULL;
- }
- /* A valid data block will always be aligned to the ID size. */
- if (WARN_ON_ONCE(blk_lpos->begin != ALIGN(blk_lpos->begin, sizeof(db->id))) ||
- WARN_ON_ONCE(blk_lpos->next != ALIGN(blk_lpos->next, sizeof(db->id)))) {
- return NULL;
- }
- /* A valid data block will always have at least an ID. */
- if (WARN_ON_ONCE(*data_size < sizeof(db->id)))
- return NULL;
- /* Subtract block ID space from size to reflect data size. */
- *data_size -= sizeof(db->id);
- return &db->data[0];
- }
- /*
- * Attempt to transition the newest descriptor from committed back to reserved
- * so that the record can be modified by a writer again. This is only possible
- * if the descriptor is not yet finalized and the provided @caller_id matches.
- */
- static struct prb_desc *desc_reopen_last(struct prb_desc_ring *desc_ring,
- u32 caller_id, unsigned long *id_out)
- {
- unsigned long prev_state_val;
- enum desc_state d_state;
- struct prb_desc desc;
- struct prb_desc *d;
- unsigned long id;
- u32 cid;
- id = atomic_long_read(&desc_ring->head_id);
- /*
- * To reduce unnecessarily reopening, first check if the descriptor
- * state and caller ID are correct.
- */
- d_state = desc_read(desc_ring, id, &desc, NULL, &cid);
- if (d_state != desc_committed || cid != caller_id)
- return NULL;
- d = to_desc(desc_ring, id);
- prev_state_val = DESC_SV(id, desc_committed);
- /*
- * Guarantee the reserved state is stored before reading any
- * record data. A full memory barrier is needed because @state_var
- * modification is followed by reading. This pairs with _prb_commit:B.
- *
- * Memory barrier involvement:
- *
- * If desc_reopen_last:A reads from _prb_commit:B, then
- * prb_reserve_in_last:A reads from _prb_commit:A.
- *
- * Relies on:
- *
- * WMB from _prb_commit:A to _prb_commit:B
- * matching
- * MB If desc_reopen_last:A to prb_reserve_in_last:A
- */
- if (!atomic_long_try_cmpxchg(&d->state_var, &prev_state_val,
- DESC_SV(id, desc_reserved))) { /* LMM(desc_reopen_last:A) */
- return NULL;
- }
- *id_out = id;
- return d;
- }
- /**
- * prb_reserve_in_last() - Re-reserve and extend the space in the ringbuffer
- * used by the newest record.
- *
- * @e: The entry structure to setup.
- * @rb: The ringbuffer to re-reserve and extend data in.
- * @r: The record structure to allocate buffers for.
- * @caller_id: The caller ID of the caller (reserving writer).
- * @max_size: Fail if the extended size would be greater than this.
- *
- * This is the public function available to writers to re-reserve and extend
- * data.
- *
- * The writer specifies the text size to extend (not the new total size) by
- * setting the @text_buf_size field of @r. To ensure proper initialization
- * of @r, prb_rec_init_wr() should be used.
- *
- * This function will fail if @caller_id does not match the caller ID of the
- * newest record. In that case the caller must reserve new data using
- * prb_reserve().
- *
- * Context: Any context. Disables local interrupts on success.
- * Return: true if text data could be extended, otherwise false.
- *
- * On success:
- *
- * - @r->text_buf points to the beginning of the entire text buffer.
- *
- * - @r->text_buf_size is set to the new total size of the buffer.
- *
- * - @r->info is not touched so that @r->info->text_len could be used
- * to append the text.
- *
- * - prb_record_text_space() can be used on @e to query the new
- * actually used space.
- *
- * Important: All @r->info fields will already be set with the current values
- * for the record. I.e. @r->info->text_len will be less than
- * @text_buf_size. Writers can use @r->info->text_len to know
- * where concatenation begins and writers should update
- * @r->info->text_len after concatenating.
- */
- bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,
- struct printk_record *r, u32 caller_id, unsigned int max_size)
- {
- struct prb_desc_ring *desc_ring = &rb->desc_ring;
- struct printk_info *info;
- unsigned int data_size;
- struct prb_desc *d;
- unsigned long id;
- local_irq_save(e->irqflags);
- /* Transition the newest descriptor back to the reserved state. */
- d = desc_reopen_last(desc_ring, caller_id, &id);
- if (!d) {
- local_irq_restore(e->irqflags);
- goto fail_reopen;
- }
- /* Now the writer has exclusive access: LMM(prb_reserve_in_last:A) */
- info = to_info(desc_ring, id);
- /*
- * Set the @e fields here so that prb_commit() can be used if
- * anything fails from now on.
- */
- e->rb = rb;
- e->id = id;
- /*
- * desc_reopen_last() checked the caller_id, but there was no
- * exclusive access at that point. The descriptor may have
- * changed since then.
- */
- if (caller_id != info->caller_id)
- goto fail;
- if (BLK_DATALESS(&d->text_blk_lpos)) {
- if (WARN_ON_ONCE(info->text_len != 0)) {
- pr_warn_once("wrong text_len value (%hu, expecting 0)\n",
- info->text_len);
- info->text_len = 0;
- }
- if (!data_check_size(&rb->text_data_ring, r->text_buf_size))
- goto fail;
- if (r->text_buf_size > max_size)
- goto fail;
- r->text_buf = data_alloc(rb, &rb->text_data_ring, r->text_buf_size,
- &d->text_blk_lpos, id);
- } else {
- if (!get_data(&rb->text_data_ring, &d->text_blk_lpos, &data_size))
- goto fail;
- /*
- * Increase the buffer size to include the original size. If
- * the meta data (@text_len) is not sane, use the full data
- * block size.
- */
- if (WARN_ON_ONCE(info->text_len > data_size)) {
- pr_warn_once("wrong text_len value (%hu, expecting <=%u)\n",
- info->text_len, data_size);
- info->text_len = data_size;
- }
- r->text_buf_size += info->text_len;
- if (!data_check_size(&rb->text_data_ring, r->text_buf_size))
- goto fail;
- if (r->text_buf_size > max_size)
- goto fail;
- r->text_buf = data_realloc(rb, &rb->text_data_ring, r->text_buf_size,
- &d->text_blk_lpos, id);
- }
- if (r->text_buf_size && !r->text_buf)
- goto fail;
- r->info = info;
- e->text_space = space_used(&rb->text_data_ring, &d->text_blk_lpos);
- return true;
- fail:
- prb_commit(e);
- /* prb_commit() re-enabled interrupts. */
- fail_reopen:
- /* Make it clear to the caller that the re-reserve failed. */
- memset(r, 0, sizeof(*r));
- return false;
- }
- /*
- * Attempt to finalize a specified descriptor. If this fails, the descriptor
- * is either already final or it will finalize itself when the writer commits.
- */
- static void desc_make_final(struct prb_desc_ring *desc_ring, unsigned long id)
- {
- unsigned long prev_state_val = DESC_SV(id, desc_committed);
- struct prb_desc *d = to_desc(desc_ring, id);
- atomic_long_cmpxchg_relaxed(&d->state_var, prev_state_val,
- DESC_SV(id, desc_finalized)); /* LMM(desc_make_final:A) */
- /* Best effort to remember the last finalized @id. */
- atomic_long_set(&desc_ring->last_finalized_id, id);
- }
- /**
- * prb_reserve() - Reserve space in the ringbuffer.
- *
- * @e: The entry structure to setup.
- * @rb: The ringbuffer to reserve data in.
- * @r: The record structure to allocate buffers for.
- *
- * This is the public function available to writers to reserve data.
- *
- * The writer specifies the text size to reserve by setting the
- * @text_buf_size field of @r. To ensure proper initialization of @r,
- * prb_rec_init_wr() should be used.
- *
- * Context: Any context. Disables local interrupts on success.
- * Return: true if at least text data could be allocated, otherwise false.
- *
- * On success, the fields @info and @text_buf of @r will be set by this
- * function and should be filled in by the writer before committing. Also
- * on success, prb_record_text_space() can be used on @e to query the actual
- * space used for the text data block.
- *
- * Important: @info->text_len needs to be set correctly by the writer in
- * order for data to be readable and/or extended. Its value
- * is initialized to 0.
- */
- bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,
- struct printk_record *r)
- {
- struct prb_desc_ring *desc_ring = &rb->desc_ring;
- struct printk_info *info;
- struct prb_desc *d;
- unsigned long id;
- u64 seq;
- if (!data_check_size(&rb->text_data_ring, r->text_buf_size))
- goto fail;
- /*
- * Descriptors in the reserved state act as blockers to all further
- * reservations once the desc_ring has fully wrapped. Disable
- * interrupts during the reserve/commit window in order to minimize
- * the likelihood of this happening.
- */
- local_irq_save(e->irqflags);
- if (!desc_reserve(rb, &id)) {
- /* Descriptor reservation failures are tracked. */
- atomic_long_inc(&rb->fail);
- local_irq_restore(e->irqflags);
- goto fail;
- }
- d = to_desc(desc_ring, id);
- info = to_info(desc_ring, id);
- /*
- * All @info fields (except @seq) are cleared and must be filled in
- * by the writer. Save @seq before clearing because it is used to
- * determine the new sequence number.
- */
- seq = info->seq;
- memset(info, 0, sizeof(*info));
- /*
- * Set the @e fields here so that prb_commit() can be used if
- * text data allocation fails.
- */
- e->rb = rb;
- e->id = id;
- /*
- * Initialize the sequence number if it has "never been set".
- * Otherwise just increment it by a full wrap.
- *
- * @seq is considered "never been set" if it has a value of 0,
- * _except_ for @infos[0], which was specially setup by the ringbuffer
- * initializer and therefore is always considered as set.
- *
- * See the "Bootstrap" comment block in printk_ringbuffer.h for
- * details about how the initializer bootstraps the descriptors.
- */
- if (seq == 0 && DESC_INDEX(desc_ring, id) != 0)
- info->seq = DESC_INDEX(desc_ring, id);
- else
- info->seq = seq + DESCS_COUNT(desc_ring);
- /*
- * New data is about to be reserved. Once that happens, previous
- * descriptors are no longer able to be extended. Finalize the
- * previous descriptor now so that it can be made available to
- * readers. (For seq==0 there is no previous descriptor.)
- */
- if (info->seq > 0)
- desc_make_final(desc_ring, DESC_ID(id - 1));
- r->text_buf = data_alloc(rb, &rb->text_data_ring, r->text_buf_size,
- &d->text_blk_lpos, id);
- /* If text data allocation fails, a data-less record is committed. */
- if (r->text_buf_size && !r->text_buf) {
- prb_commit(e);
- /* prb_commit() re-enabled interrupts. */
- goto fail;
- }
- r->info = info;
- /* Record full text space used by record. */
- e->text_space = space_used(&rb->text_data_ring, &d->text_blk_lpos);
- return true;
- fail:
- /* Make it clear to the caller that the reserve failed. */
- memset(r, 0, sizeof(*r));
- return false;
- }
- /* Commit the data (possibly finalizing it) and restore interrupts. */
- static void _prb_commit(struct prb_reserved_entry *e, unsigned long state_val)
- {
- struct prb_desc_ring *desc_ring = &e->rb->desc_ring;
- struct prb_desc *d = to_desc(desc_ring, e->id);
- unsigned long prev_state_val = DESC_SV(e->id, desc_reserved);
- /* Now the writer has finished all writing: LMM(_prb_commit:A) */
- /*
- * Set the descriptor as committed. See "ABA Issues" about why
- * cmpxchg() instead of set() is used.
- *
- * 1 Guarantee all record data is stored before the descriptor state
- * is stored as committed. A write memory barrier is sufficient
- * for this. This pairs with desc_read:B and desc_reopen_last:A.
- *
- * 2. Guarantee the descriptor state is stored as committed before
- * re-checking the head ID in order to possibly finalize this
- * descriptor. This pairs with desc_reserve:D.
- *
- * Memory barrier involvement:
- *
- * If prb_commit:A reads from desc_reserve:D, then
- * desc_make_final:A reads from _prb_commit:B.
- *
- * Relies on:
- *
- * MB _prb_commit:B to prb_commit:A
- * matching
- * MB desc_reserve:D to desc_make_final:A
- */
- if (!atomic_long_try_cmpxchg(&d->state_var, &prev_state_val,
- DESC_SV(e->id, state_val))) { /* LMM(_prb_commit:B) */
- WARN_ON_ONCE(1);
- }
- /* Restore interrupts, the reserve/commit window is finished. */
- local_irq_restore(e->irqflags);
- }
- /**
- * prb_commit() - Commit (previously reserved) data to the ringbuffer.
- *
- * @e: The entry containing the reserved data information.
- *
- * This is the public function available to writers to commit data.
- *
- * Note that the data is not yet available to readers until it is finalized.
- * Finalizing happens automatically when space for the next record is
- * reserved.
- *
- * See prb_final_commit() for a version of this function that finalizes
- * immediately.
- *
- * Context: Any context. Enables local interrupts.
- */
- void prb_commit(struct prb_reserved_entry *e)
- {
- struct prb_desc_ring *desc_ring = &e->rb->desc_ring;
- unsigned long head_id;
- _prb_commit(e, desc_committed);
- /*
- * If this descriptor is no longer the head (i.e. a new record has
- * been allocated), extending the data for this record is no longer
- * allowed and therefore it must be finalized.
- */
- head_id = atomic_long_read(&desc_ring->head_id); /* LMM(prb_commit:A) */
- if (head_id != e->id)
- desc_make_final(desc_ring, e->id);
- }
- /**
- * prb_final_commit() - Commit and finalize (previously reserved) data to
- * the ringbuffer.
- *
- * @e: The entry containing the reserved data information.
- *
- * This is the public function available to writers to commit+finalize data.
- *
- * By finalizing, the data is made immediately available to readers.
- *
- * This function should only be used if there are no intentions of extending
- * this data using prb_reserve_in_last().
- *
- * Context: Any context. Enables local interrupts.
- */
- void prb_final_commit(struct prb_reserved_entry *e)
- {
- struct prb_desc_ring *desc_ring = &e->rb->desc_ring;
- _prb_commit(e, desc_finalized);
- /* Best effort to remember the last finalized @id. */
- atomic_long_set(&desc_ring->last_finalized_id, e->id);
- }
- /*
- * Count the number of lines in provided text. All text has at least 1 line
- * (even if @text_size is 0). Each '\n' processed is counted as an additional
- * line.
- */
- static unsigned int count_lines(const char *text, unsigned int text_size)
- {
- unsigned int next_size = text_size;
- unsigned int line_count = 1;
- const char *next = text;
- while (next_size) {
- next = memchr(next, '\n', next_size);
- if (!next)
- break;
- line_count++;
- next++;
- next_size = text_size - (next - text);
- }
- return line_count;
- }
- /*
- * Given @blk_lpos, copy an expected @len of data into the provided buffer.
- * If @line_count is provided, count the number of lines in the data.
- *
- * This function (used by readers) performs strict validation on the data
- * size to possibly detect bugs in the writer code. A WARN_ON_ONCE() is
- * triggered if an internal error is detected.
- */
- static bool copy_data(struct prb_data_ring *data_ring,
- struct prb_data_blk_lpos *blk_lpos, u16 len, char *buf,
- unsigned int buf_size, unsigned int *line_count)
- {
- unsigned int data_size;
- const char *data;
- /* Caller might not want any data. */
- if ((!buf || !buf_size) && !line_count)
- return true;
- data = get_data(data_ring, blk_lpos, &data_size);
- if (!data)
- return false;
- /*
- * Actual cannot be less than expected. It can be more than expected
- * because of the trailing alignment padding.
- *
- * Note that invalid @len values can occur because the caller loads
- * the value during an allowed data race.
- */
- if (data_size < (unsigned int)len)
- return false;
- /* Caller interested in the line count? */
- if (line_count)
- *line_count = count_lines(data, len);
- /* Caller interested in the data content? */
- if (!buf || !buf_size)
- return true;
- data_size = min_t(u16, buf_size, len);
- memcpy(&buf[0], data, data_size); /* LMM(copy_data:A) */
- return true;
- }
- /*
- * This is an extended version of desc_read(). It gets a copy of a specified
- * descriptor. However, it also verifies that the record is finalized and has
- * the sequence number @seq. On success, 0 is returned.
- *
- * Error return values:
- * -EINVAL: A finalized record with sequence number @seq does not exist.
- * -ENOENT: A finalized record with sequence number @seq exists, but its data
- * is not available. This is a valid record, so readers should
- * continue with the next record.
- */
- static int desc_read_finalized_seq(struct prb_desc_ring *desc_ring,
- unsigned long id, u64 seq,
- struct prb_desc *desc_out)
- {
- struct prb_data_blk_lpos *blk_lpos = &desc_out->text_blk_lpos;
- enum desc_state d_state;
- u64 s;
- d_state = desc_read(desc_ring, id, desc_out, &s, NULL);
- /*
- * An unexpected @id (desc_miss) or @seq mismatch means the record
- * does not exist. A descriptor in the reserved or committed state
- * means the record does not yet exist for the reader.
- */
- if (d_state == desc_miss ||
- d_state == desc_reserved ||
- d_state == desc_committed ||
- s != seq) {
- return -EINVAL;
- }
- /*
- * A descriptor in the reusable state may no longer have its data
- * available; report it as existing but with lost data. Or the record
- * may actually be a record with lost data.
- */
- if (d_state == desc_reusable ||
- (blk_lpos->begin == FAILED_LPOS && blk_lpos->next == FAILED_LPOS)) {
- return -ENOENT;
- }
- return 0;
- }
- /*
- * Copy the ringbuffer data from the record with @seq to the provided
- * @r buffer. On success, 0 is returned.
- *
- * See desc_read_finalized_seq() for error return values.
- */
- static int prb_read(struct printk_ringbuffer *rb, u64 seq,
- struct printk_record *r, unsigned int *line_count)
- {
- struct prb_desc_ring *desc_ring = &rb->desc_ring;
- struct printk_info *info = to_info(desc_ring, seq);
- struct prb_desc *rdesc = to_desc(desc_ring, seq);
- atomic_long_t *state_var = &rdesc->state_var;
- struct prb_desc desc;
- unsigned long id;
- int err;
- /* Extract the ID, used to specify the descriptor to read. */
- id = DESC_ID(atomic_long_read(state_var));
- /* Get a local copy of the correct descriptor (if available). */
- err = desc_read_finalized_seq(desc_ring, id, seq, &desc);
- /*
- * If @r is NULL, the caller is only interested in the availability
- * of the record.
- */
- if (err || !r)
- return err;
- /* If requested, copy meta data. */
- if (r->info)
- memcpy(r->info, info, sizeof(*(r->info)));
- /* Copy text data. If it fails, this is a data-less record. */
- if (!copy_data(&rb->text_data_ring, &desc.text_blk_lpos, info->text_len,
- r->text_buf, r->text_buf_size, line_count)) {
- return -ENOENT;
- }
- /* Ensure the record is still finalized and has the same @seq. */
- return desc_read_finalized_seq(desc_ring, id, seq, &desc);
- }
- /* Get the sequence number of the tail descriptor. */
- static u64 prb_first_seq(struct printk_ringbuffer *rb)
- {
- struct prb_desc_ring *desc_ring = &rb->desc_ring;
- enum desc_state d_state;
- struct prb_desc desc;
- unsigned long id;
- u64 seq;
- for (;;) {
- id = atomic_long_read(&rb->desc_ring.tail_id); /* LMM(prb_first_seq:A) */
- d_state = desc_read(desc_ring, id, &desc, &seq, NULL); /* LMM(prb_first_seq:B) */
- /*
- * This loop will not be infinite because the tail is
- * _always_ in the finalized or reusable state.
- */
- if (d_state == desc_finalized || d_state == desc_reusable)
- break;
- /*
- * Guarantee the last state load from desc_read() is before
- * reloading @tail_id in order to see a new tail in the case
- * that the descriptor has been recycled. This pairs with
- * desc_reserve:D.
- *
- * Memory barrier involvement:
- *
- * If prb_first_seq:B reads from desc_reserve:F, then
- * prb_first_seq:A reads from desc_push_tail:B.
- *
- * Relies on:
- *
- * MB from desc_push_tail:B to desc_reserve:F
- * matching
- * RMB prb_first_seq:B to prb_first_seq:A
- */
- smp_rmb(); /* LMM(prb_first_seq:C) */
- }
- return seq;
- }
- /*
- * Non-blocking read of a record. Updates @seq to the last finalized record
- * (which may have no data available).
- *
- * See the description of prb_read_valid() and prb_read_valid_info()
- * for details.
- */
- static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
- struct printk_record *r, unsigned int *line_count)
- {
- u64 tail_seq;
- int err;
- while ((err = prb_read(rb, *seq, r, line_count))) {
- tail_seq = prb_first_seq(rb);
- if (*seq < tail_seq) {
- /*
- * Behind the tail. Catch up and try again. This
- * can happen for -ENOENT and -EINVAL cases.
- */
- *seq = tail_seq;
- } else if (err == -ENOENT) {
- /* Record exists, but no data available. Skip. */
- (*seq)++;
- } else {
- /* Non-existent/non-finalized record. Must stop. */
- return false;
- }
- }
- return true;
- }
- /**
- * prb_read_valid() - Non-blocking read of a requested record or (if gone)
- * the next available record.
- *
- * @rb: The ringbuffer to read from.
- * @seq: The sequence number of the record to read.
- * @r: A record data buffer to store the read record to.
- *
- * This is the public function available to readers to read a record.
- *
- * The reader provides the @info and @text_buf buffers of @r to be
- * filled in. Any of the buffer pointers can be set to NULL if the reader
- * is not interested in that data. To ensure proper initialization of @r,
- * prb_rec_init_rd() should be used.
- *
- * Context: Any context.
- * Return: true if a record was read, otherwise false.
- *
- * On success, the reader must check r->info.seq to see which record was
- * actually read. This allows the reader to detect dropped records.
- *
- * Failure means @seq refers to a not yet written record.
- */
- bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq,
- struct printk_record *r)
- {
- return _prb_read_valid(rb, &seq, r, NULL);
- }
- /**
- * prb_read_valid_info() - Non-blocking read of meta data for a requested
- * record or (if gone) the next available record.
- *
- * @rb: The ringbuffer to read from.
- * @seq: The sequence number of the record to read.
- * @info: A buffer to store the read record meta data to.
- * @line_count: A buffer to store the number of lines in the record text.
- *
- * This is the public function available to readers to read only the
- * meta data of a record.
- *
- * The reader provides the @info, @line_count buffers to be filled in.
- * Either of the buffer pointers can be set to NULL if the reader is not
- * interested in that data.
- *
- * Context: Any context.
- * Return: true if a record's meta data was read, otherwise false.
- *
- * On success, the reader must check info->seq to see which record meta data
- * was actually read. This allows the reader to detect dropped records.
- *
- * Failure means @seq refers to a not yet written record.
- */
- bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq,
- struct printk_info *info, unsigned int *line_count)
- {
- struct printk_record r;
- prb_rec_init_rd(&r, info, NULL, 0);
- return _prb_read_valid(rb, &seq, &r, line_count);
- }
- /**
- * prb_first_valid_seq() - Get the sequence number of the oldest available
- * record.
- *
- * @rb: The ringbuffer to get the sequence number from.
- *
- * This is the public function available to readers to see what the
- * first/oldest valid sequence number is.
- *
- * This provides readers a starting point to begin iterating the ringbuffer.
- *
- * Context: Any context.
- * Return: The sequence number of the first/oldest record or, if the
- * ringbuffer is empty, 0 is returned.
- */
- u64 prb_first_valid_seq(struct printk_ringbuffer *rb)
- {
- u64 seq = 0;
- if (!_prb_read_valid(rb, &seq, NULL, NULL))
- return 0;
- return seq;
- }
- /**
- * prb_next_seq() - Get the sequence number after the last available record.
- *
- * @rb: The ringbuffer to get the sequence number from.
- *
- * This is the public function available to readers to see what the next
- * newest sequence number available to readers will be.
- *
- * This provides readers a sequence number to jump to if all currently
- * available records should be skipped.
- *
- * Context: Any context.
- * Return: The sequence number of the next newest (not yet available) record
- * for readers.
- */
- u64 prb_next_seq(struct printk_ringbuffer *rb)
- {
- struct prb_desc_ring *desc_ring = &rb->desc_ring;
- enum desc_state d_state;
- unsigned long id;
- u64 seq;
- /* Check if the cached @id still points to a valid @seq. */
- id = atomic_long_read(&desc_ring->last_finalized_id);
- d_state = desc_read(desc_ring, id, NULL, &seq, NULL);
- if (d_state == desc_finalized || d_state == desc_reusable) {
- /*
- * Begin searching after the last finalized record.
- *
- * On 0, the search must begin at 0 because of hack#2
- * of the bootstrapping phase it is not known if a
- * record at index 0 exists.
- */
- if (seq != 0)
- seq++;
- } else {
- /*
- * The information about the last finalized sequence number
- * has gone. It should happen only when there is a flood of
- * new messages and the ringbuffer is rapidly recycled.
- * Give up and start from the beginning.
- */
- seq = 0;
- }
- /*
- * The information about the last finalized @seq might be inaccurate.
- * Search forward to find the current one.
- */
- while (_prb_read_valid(rb, &seq, NULL, NULL))
- seq++;
- return seq;
- }
- /**
- * prb_init() - Initialize a ringbuffer to use provided external buffers.
- *
- * @rb: The ringbuffer to initialize.
- * @text_buf: The data buffer for text data.
- * @textbits: The size of @text_buf as a power-of-2 value.
- * @descs: The descriptor buffer for ringbuffer records.
- * @descbits: The count of @descs items as a power-of-2 value.
- * @infos: The printk_info buffer for ringbuffer records.
- *
- * This is the public function available to writers to setup a ringbuffer
- * during runtime using provided buffers.
- *
- * This must match the initialization of DEFINE_PRINTKRB().
- *
- * Context: Any context.
- */
- void prb_init(struct printk_ringbuffer *rb,
- char *text_buf, unsigned int textbits,
- struct prb_desc *descs, unsigned int descbits,
- struct printk_info *infos)
- {
- memset(descs, 0, _DESCS_COUNT(descbits) * sizeof(descs[0]));
- memset(infos, 0, _DESCS_COUNT(descbits) * sizeof(infos[0]));
- rb->desc_ring.count_bits = descbits;
- rb->desc_ring.descs = descs;
- rb->desc_ring.infos = infos;
- atomic_long_set(&rb->desc_ring.head_id, DESC0_ID(descbits));
- atomic_long_set(&rb->desc_ring.tail_id, DESC0_ID(descbits));
- atomic_long_set(&rb->desc_ring.last_finalized_id, DESC0_ID(descbits));
- rb->text_data_ring.size_bits = textbits;
- rb->text_data_ring.data = text_buf;
- atomic_long_set(&rb->text_data_ring.head_lpos, BLK0_LPOS(textbits));
- atomic_long_set(&rb->text_data_ring.tail_lpos, BLK0_LPOS(textbits));
- atomic_long_set(&rb->fail, 0);
- atomic_long_set(&(descs[_DESCS_COUNT(descbits) - 1].state_var), DESC0_SV(descbits));
- descs[_DESCS_COUNT(descbits) - 1].text_blk_lpos.begin = FAILED_LPOS;
- descs[_DESCS_COUNT(descbits) - 1].text_blk_lpos.next = FAILED_LPOS;
- infos[0].seq = -(u64)_DESCS_COUNT(descbits);
- infos[_DESCS_COUNT(descbits) - 1].seq = 0;
- }
- /**
- * prb_record_text_space() - Query the full actual used ringbuffer space for
- * the text data of a reserved entry.
- *
- * @e: The successfully reserved entry to query.
- *
- * This is the public function available to writers to see how much actual
- * space is used in the ringbuffer to store the text data of the specified
- * entry.
- *
- * This function is only valid if @e has been successfully reserved using
- * prb_reserve().
- *
- * Context: Any context.
- * Return: The size in bytes used by the text data of the associated record.
- */
- unsigned int prb_record_text_space(struct prb_reserved_entry *e)
- {
- return e->text_space;
- }
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