1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991001011021031041051061071081091101111121131141151161171181191201211221231241251261271281291301311321331341351361371381391401411421431441451461471481491501511521531541551561571581591601611621631641651661671681691701711721731741751761771781791801811821831841851861871881891901911921931941951961971981992002012022032042052062072082092102112122132142152162172182192202212222232242252262272282292302312322332342352362372382392402412422432442452462472482492502512522532542552562572582592602612622632642652662672682692702712722732742752762772782792802812822832842852862872882892902912922932942952962972982993003013023033043053063073083093103113123133143153163173183193203213223233243253263273283293303313323333343353363373383393403413423433443453463473483493503513523533543553563573583593603613623633643653663673683693703713723733743753763773783793803813823833843853863873883893903913923933943953963973983994004014024034044054064074084094104114124134144154164174184194204214224234244254264274284294304314324334344354364374384394404414424434444454464474484494504514524534544554564574584594604614624634644654664674684694704714724734744754764774784794804814824834844854864874884894904914924934944954964974984995005015025035045055065075085095105115125135145155165175185195205215225235245255265275285295305315325335345355365375385395405415425435445455465475485495505515525535545555565575585595605615625635645655665675685695705715725735745755765775785795805815825835845855865875885895905915925935945955965975985996006016026036046056066076086096106116126136146156166176186196206216226236246256266276286296306316326336346356366376386396406416426436446456466476486496506516526536546556566576586596606616626636646656666676686696706716726736746756766776786796806816826836846856866876886896906916926936946956966976986997007017027037047057067077087097107117127137147157167177187197207217227237247257267277287297307317327337347357367377387397407417427437447457467477487497507517527537547557567577587597607617627637647657667677687697707717727737747757767777787797807817827837847857867877887897907917927937947957967977987998008018028038048058068078088098108118128138148158168178188198208218228238248258268278288298308318328338348358368378388398408418428438448458468478488498508518528538548558568578588598608618628638648658668678688698708718728738748758768778788798808818828838848858868878888898908918928938948958968978988999009019029039049059069079089099109119129139149159169179189199209219229239249259269279289299309319329339349359369379389399409419429439449459469479489499509519529539549559569579589599609619629639649659669679689699709719729739749759769779789799809819829839849859869879889899909919929939949959969979989991000100110021003100410051006100710081009101010111012101310141015101610171018101910201021102210231024102510261027102810291030103110321033103410351036103710381039104010411042104310441045104610471048104910501051105210531054105510561057105810591060106110621063106410651066106710681069107010711072107310741075107610771078107910801081108210831084108510861087108810891090109110921093109410951096109710981099110011011102110311041105110611071108110911101111111211131114111511161117111811191120112111221123112411251126112711281129113011311132113311341135113611371138113911401141114211431144114511461147114811491150115111521153115411551156115711581159116011611162116311641165116611671168116911701171117211731174117511761177117811791180118111821183118411851186118711881189119011911192119311941195119611971198119912001201120212031204120512061207120812091210121112121213121412151216121712181219122012211222122312241225122612271228122912301231123212331234123512361237123812391240124112421243124412451246124712481249125012511252125312541255125612571258125912601261126212631264126512661267126812691270127112721273127412751276127712781279128012811282128312841285128612871288128912901291129212931294129512961297129812991300130113021303130413051306130713081309131013111312131313141315131613171318131913201321132213231324132513261327132813291330133113321333133413351336133713381339134013411342134313441345134613471348134913501351135213531354135513561357135813591360136113621363136413651366136713681369137013711372137313741375137613771378137913801381138213831384138513861387138813891390139113921393139413951396139713981399140014011402140314041405140614071408140914101411141214131414141514161417141814191420142114221423142414251426142714281429143014311432143314341435143614371438143914401441144214431444144514461447144814491450145114521453145414551456145714581459146014611462146314641465146614671468146914701471147214731474147514761477147814791480148114821483148414851486148714881489149014911492149314941495149614971498149915001501150215031504150515061507150815091510151115121513151415151516151715181519152015211522152315241525152615271528152915301531153215331534153515361537153815391540154115421543154415451546154715481549155015511552155315541555155615571558155915601561156215631564156515661567156815691570157115721573157415751576157715781579158015811582158315841585158615871588158915901591159215931594159515961597159815991600160116021603160416051606160716081609161016111612161316141615161616171618161916201621162216231624162516261627162816291630163116321633163416351636163716381639164016411642164316441645164616471648164916501651165216531654165516561657165816591660166116621663166416651666166716681669167016711672167316741675167616771678167916801681168216831684168516861687168816891690169116921693169416951696169716981699170017011702170317041705170617071708170917101711 |
- // SPDX-License-Identifier: GPL-2.0
- /* kernel/rwsem.c: R/W semaphores, public implementation
- *
- * Written by David Howells (dhowells@redhat.com).
- * Derived from asm-i386/semaphore.h
- *
- * Writer lock-stealing by Alex Shi <alex.shi@intel.com>
- * and Michel Lespinasse <walken@google.com>
- *
- * Optimistic spinning by Tim Chen <tim.c.chen@intel.com>
- * and Davidlohr Bueso <davidlohr@hp.com>. Based on mutexes.
- *
- * Rwsem count bit fields re-definition and rwsem rearchitecture by
- * Waiman Long <longman@redhat.com> and
- * Peter Zijlstra <peterz@infradead.org>.
- */
- #include <linux/types.h>
- #include <linux/kernel.h>
- #include <linux/sched.h>
- #include <linux/sched/rt.h>
- #include <linux/sched/task.h>
- #include <linux/sched/debug.h>
- #include <linux/sched/wake_q.h>
- #include <linux/sched/signal.h>
- #include <linux/sched/clock.h>
- #include <linux/export.h>
- #include <linux/rwsem.h>
- #include <linux/atomic.h>
- #include "lock_events.h"
- #include <trace/hooks/rwsem.h>
- #include <trace/hooks/dtask.h>
- /*
- * The least significant 3 bits of the owner value has the following
- * meanings when set.
- * - Bit 0: RWSEM_READER_OWNED - The rwsem is owned by readers
- * - Bit 1: RWSEM_RD_NONSPINNABLE - Readers cannot spin on this lock.
- * - Bit 2: RWSEM_WR_NONSPINNABLE - Writers cannot spin on this lock.
- *
- * When the rwsem is either owned by an anonymous writer, or it is
- * reader-owned, but a spinning writer has timed out, both nonspinnable
- * bits will be set to disable optimistic spinning by readers and writers.
- * In the later case, the last unlocking reader should then check the
- * writer nonspinnable bit and clear it only to give writers preference
- * to acquire the lock via optimistic spinning, but not readers. Similar
- * action is also done in the reader slowpath.
- * When a writer acquires a rwsem, it puts its task_struct pointer
- * into the owner field. It is cleared after an unlock.
- *
- * When a reader acquires a rwsem, it will also puts its task_struct
- * pointer into the owner field with the RWSEM_READER_OWNED bit set.
- * On unlock, the owner field will largely be left untouched. So
- * for a free or reader-owned rwsem, the owner value may contain
- * information about the last reader that acquires the rwsem.
- *
- * That information may be helpful in debugging cases where the system
- * seems to hang on a reader owned rwsem especially if only one reader
- * is involved. Ideally we would like to track all the readers that own
- * a rwsem, but the overhead is simply too big.
- *
- * Reader optimistic spinning is helpful when the reader critical section
- * is short and there aren't that many readers around. It makes readers
- * relatively more preferred than writers. When a writer times out spinning
- * on a reader-owned lock and set the nospinnable bits, there are two main
- * reasons for that.
- *
- * 1) The reader critical section is long, perhaps the task sleeps after
- * acquiring the read lock.
- * 2) There are just too many readers contending the lock causing it to
- * take a while to service all of them.
- *
- * In the former case, long reader critical section will impede the progress
- * of writers which is usually more important for system performance. In
- * the later case, reader optimistic spinning tends to make the reader
- * groups that contain readers that acquire the lock together smaller
- * leading to more of them. That may hurt performance in some cases. In
- * other words, the setting of nonspinnable bits indicates that reader
- * optimistic spinning may not be helpful for those workloads that cause
- * it.
- *
- * Therefore, any writers that had observed the setting of the writer
- * nonspinnable bit for a given rwsem after they fail to acquire the lock
- * via optimistic spinning will set the reader nonspinnable bit once they
- * acquire the write lock. Similarly, readers that observe the setting
- * of reader nonspinnable bit at slowpath entry will set the reader
- * nonspinnable bits when they acquire the read lock via the wakeup path.
- *
- * Once the reader nonspinnable bit is on, it will only be reset when
- * a writer is able to acquire the rwsem in the fast path or somehow a
- * reader or writer in the slowpath doesn't observe the nonspinable bit.
- *
- * This is to discourage reader optmistic spinning on that particular
- * rwsem and make writers more preferred. This adaptive disabling of reader
- * optimistic spinning will alleviate the negative side effect of this
- * feature.
- */
- #define RWSEM_READER_OWNED (1UL << 0)
- #define RWSEM_RD_NONSPINNABLE (1UL << 1)
- #define RWSEM_WR_NONSPINNABLE (1UL << 2)
- #define RWSEM_NONSPINNABLE (RWSEM_RD_NONSPINNABLE | RWSEM_WR_NONSPINNABLE)
- #define RWSEM_OWNER_FLAGS_MASK (RWSEM_READER_OWNED | RWSEM_NONSPINNABLE)
- #ifdef CONFIG_DEBUG_RWSEMS
- # define DEBUG_RWSEMS_WARN_ON(c, sem) do { \
- if (!debug_locks_silent && \
- WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, magic = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
- #c, atomic_long_read(&(sem)->count), \
- (unsigned long) sem->magic, \
- atomic_long_read(&(sem)->owner), (long)current, \
- list_empty(&(sem)->wait_list) ? "" : "not ")) \
- debug_locks_off(); \
- } while (0)
- #else
- # define DEBUG_RWSEMS_WARN_ON(c, sem)
- #endif
- /*
- * On 64-bit architectures, the bit definitions of the count are:
- *
- * Bit 0 - writer locked bit
- * Bit 1 - waiters present bit
- * Bit 2 - lock handoff bit
- * Bits 3-7 - reserved
- * Bits 8-62 - 55-bit reader count
- * Bit 63 - read fail bit
- *
- * On 32-bit architectures, the bit definitions of the count are:
- *
- * Bit 0 - writer locked bit
- * Bit 1 - waiters present bit
- * Bit 2 - lock handoff bit
- * Bits 3-7 - reserved
- * Bits 8-30 - 23-bit reader count
- * Bit 31 - read fail bit
- *
- * It is not likely that the most significant bit (read fail bit) will ever
- * be set. This guard bit is still checked anyway in the down_read() fastpath
- * just in case we need to use up more of the reader bits for other purpose
- * in the future.
- *
- * atomic_long_fetch_add() is used to obtain reader lock, whereas
- * atomic_long_cmpxchg() will be used to obtain writer lock.
- *
- * There are three places where the lock handoff bit may be set or cleared.
- * 1) rwsem_mark_wake() for readers.
- * 2) rwsem_try_write_lock() for writers.
- * 3) Error path of rwsem_down_write_slowpath().
- *
- * For all the above cases, wait_lock will be held. A writer must also
- * be the first one in the wait_list to be eligible for setting the handoff
- * bit. So concurrent setting/clearing of handoff bit is not possible.
- */
- #define RWSEM_WRITER_LOCKED (1UL << 0)
- #define RWSEM_FLAG_WAITERS (1UL << 1)
- #define RWSEM_FLAG_HANDOFF (1UL << 2)
- #define RWSEM_FLAG_READFAIL (1UL << (BITS_PER_LONG - 1))
- #define RWSEM_READER_SHIFT 8
- #define RWSEM_READER_BIAS (1UL << RWSEM_READER_SHIFT)
- #define RWSEM_READER_MASK (~(RWSEM_READER_BIAS - 1))
- #define RWSEM_WRITER_MASK RWSEM_WRITER_LOCKED
- #define RWSEM_LOCK_MASK (RWSEM_WRITER_MASK|RWSEM_READER_MASK)
- #define RWSEM_READ_FAILED_MASK (RWSEM_WRITER_MASK|RWSEM_FLAG_WAITERS|\
- RWSEM_FLAG_HANDOFF|RWSEM_FLAG_READFAIL)
- /*
- * All writes to owner are protected by WRITE_ONCE() to make sure that
- * store tearing can't happen as optimistic spinners may read and use
- * the owner value concurrently without lock. Read from owner, however,
- * may not need READ_ONCE() as long as the pointer value is only used
- * for comparison and isn't being dereferenced.
- */
- static inline void rwsem_set_owner(struct rw_semaphore *sem)
- {
- atomic_long_set(&sem->owner, (long)current);
- trace_android_vh_rwsem_set_owner(sem);
- }
- static inline void rwsem_clear_owner(struct rw_semaphore *sem)
- {
- atomic_long_set(&sem->owner, 0);
- }
- /*
- * Test the flags in the owner field.
- */
- static inline bool rwsem_test_oflags(struct rw_semaphore *sem, long flags)
- {
- return atomic_long_read(&sem->owner) & flags;
- }
- /*
- * The task_struct pointer of the last owning reader will be left in
- * the owner field.
- *
- * Note that the owner value just indicates the task has owned the rwsem
- * previously, it may not be the real owner or one of the real owners
- * anymore when that field is examined, so take it with a grain of salt.
- *
- * The reader non-spinnable bit is preserved.
- */
- static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
- struct task_struct *owner)
- {
- unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED |
- (atomic_long_read(&sem->owner) & RWSEM_RD_NONSPINNABLE);
- atomic_long_set(&sem->owner, val);
- }
- static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
- {
- __rwsem_set_reader_owned(sem, current);
- trace_android_vh_rwsem_set_reader_owned(sem);
- }
- /*
- * Return true if the rwsem is owned by a reader.
- */
- static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
- {
- #ifdef CONFIG_DEBUG_RWSEMS
- /*
- * Check the count to see if it is write-locked.
- */
- long count = atomic_long_read(&sem->count);
- if (count & RWSEM_WRITER_MASK)
- return false;
- #endif
- return rwsem_test_oflags(sem, RWSEM_READER_OWNED);
- }
- #ifdef CONFIG_DEBUG_RWSEMS
- /*
- * With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there
- * is a task pointer in owner of a reader-owned rwsem, it will be the
- * real owner or one of the real owners. The only exception is when the
- * unlock is done by up_read_non_owner().
- */
- static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
- {
- unsigned long val = atomic_long_read(&sem->owner);
- while ((val & ~RWSEM_OWNER_FLAGS_MASK) == (unsigned long)current) {
- if (atomic_long_try_cmpxchg(&sem->owner, &val,
- val & RWSEM_OWNER_FLAGS_MASK))
- return;
- }
- }
- #else
- static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
- {
- }
- #endif
- /*
- * Set the RWSEM_NONSPINNABLE bits if the RWSEM_READER_OWNED flag
- * remains set. Otherwise, the operation will be aborted.
- */
- static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
- {
- unsigned long owner = atomic_long_read(&sem->owner);
- do {
- if (!(owner & RWSEM_READER_OWNED))
- break;
- if (owner & RWSEM_NONSPINNABLE)
- break;
- } while (!atomic_long_try_cmpxchg(&sem->owner, &owner,
- owner | RWSEM_NONSPINNABLE));
- }
- static inline bool rwsem_read_trylock(struct rw_semaphore *sem)
- {
- long cnt = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
- if (WARN_ON_ONCE(cnt < 0))
- rwsem_set_nonspinnable(sem);
- return !(cnt & RWSEM_READ_FAILED_MASK);
- }
- /*
- * Return just the real task structure pointer of the owner
- */
- static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
- {
- return (struct task_struct *)
- (atomic_long_read(&sem->owner) & ~RWSEM_OWNER_FLAGS_MASK);
- }
- /*
- * Return the real task structure pointer of the owner and the embedded
- * flags in the owner. pflags must be non-NULL.
- */
- static inline struct task_struct *
- rwsem_owner_flags(struct rw_semaphore *sem, unsigned long *pflags)
- {
- unsigned long owner = atomic_long_read(&sem->owner);
- *pflags = owner & RWSEM_OWNER_FLAGS_MASK;
- return (struct task_struct *)(owner & ~RWSEM_OWNER_FLAGS_MASK);
- }
- /*
- * Guide to the rw_semaphore's count field.
- *
- * When the RWSEM_WRITER_LOCKED bit in count is set, the lock is owned
- * by a writer.
- *
- * The lock is owned by readers when
- * (1) the RWSEM_WRITER_LOCKED isn't set in count,
- * (2) some of the reader bits are set in count, and
- * (3) the owner field has RWSEM_READ_OWNED bit set.
- *
- * Having some reader bits set is not enough to guarantee a readers owned
- * lock as the readers may be in the process of backing out from the count
- * and a writer has just released the lock. So another writer may steal
- * the lock immediately after that.
- */
- /*
- * Initialize an rwsem:
- */
- void __init_rwsem(struct rw_semaphore *sem, const char *name,
- struct lock_class_key *key)
- {
- #ifdef CONFIG_DEBUG_LOCK_ALLOC
- /*
- * Make sure we are not reinitializing a held semaphore:
- */
- debug_check_no_locks_freed((void *)sem, sizeof(*sem));
- lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
- #endif
- #ifdef CONFIG_DEBUG_RWSEMS
- sem->magic = sem;
- #endif
- atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
- raw_spin_lock_init(&sem->wait_lock);
- INIT_LIST_HEAD(&sem->wait_list);
- atomic_long_set(&sem->owner, 0L);
- #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
- osq_lock_init(&sem->osq);
- #endif
- trace_android_vh_rwsem_init(sem);
- }
- EXPORT_SYMBOL(__init_rwsem);
- #define rwsem_first_waiter(sem) \
- list_first_entry(&sem->wait_list, struct rwsem_waiter, list)
- enum rwsem_wake_type {
- RWSEM_WAKE_ANY, /* Wake whatever's at head of wait list */
- RWSEM_WAKE_READERS, /* Wake readers only */
- RWSEM_WAKE_READ_OWNED /* Waker thread holds the read lock */
- };
- enum writer_wait_state {
- WRITER_NOT_FIRST, /* Writer is not first in wait list */
- WRITER_FIRST, /* Writer is first in wait list */
- WRITER_HANDOFF /* Writer is first & handoff needed */
- };
- /*
- * The typical HZ value is either 250 or 1000. So set the minimum waiting
- * time to at least 4ms or 1 jiffy (if it is higher than 4ms) in the wait
- * queue before initiating the handoff protocol.
- */
- #define RWSEM_WAIT_TIMEOUT DIV_ROUND_UP(HZ, 250)
- /*
- * Magic number to batch-wakeup waiting readers, even when writers are
- * also present in the queue. This both limits the amount of work the
- * waking thread must do and also prevents any potential counter overflow,
- * however unlikely.
- */
- #define MAX_READERS_WAKEUP 0x100
- /*
- * handle the lock release when processes blocked on it that can now run
- * - if we come here from up_xxxx(), then the RWSEM_FLAG_WAITERS bit must
- * have been set.
- * - there must be someone on the queue
- * - the wait_lock must be held by the caller
- * - tasks are marked for wakeup, the caller must later invoke wake_up_q()
- * to actually wakeup the blocked task(s) and drop the reference count,
- * preferably when the wait_lock is released
- * - woken process blocks are discarded from the list after having task zeroed
- * - writers are only marked woken if downgrading is false
- */
- static void rwsem_mark_wake(struct rw_semaphore *sem,
- enum rwsem_wake_type wake_type,
- struct wake_q_head *wake_q)
- {
- struct rwsem_waiter *waiter, *tmp;
- long oldcount, woken = 0, adjustment = 0;
- struct list_head wlist;
- lockdep_assert_held(&sem->wait_lock);
- /*
- * Take a peek at the queue head waiter such that we can determine
- * the wakeup(s) to perform.
- */
- waiter = rwsem_first_waiter(sem);
- if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
- if (wake_type == RWSEM_WAKE_ANY) {
- /*
- * Mark writer at the front of the queue for wakeup.
- * Until the task is actually later awoken later by
- * the caller, other writers are able to steal it.
- * Readers, on the other hand, will block as they
- * will notice the queued writer.
- */
- wake_q_add(wake_q, waiter->task);
- lockevent_inc(rwsem_wake_writer);
- }
- return;
- }
- /*
- * No reader wakeup if there are too many of them already.
- */
- if (unlikely(atomic_long_read(&sem->count) < 0))
- return;
- /*
- * Writers might steal the lock before we grant it to the next reader.
- * We prefer to do the first reader grant before counting readers
- * so we can bail out early if a writer stole the lock.
- */
- if (wake_type != RWSEM_WAKE_READ_OWNED) {
- struct task_struct *owner;
- adjustment = RWSEM_READER_BIAS;
- oldcount = atomic_long_fetch_add(adjustment, &sem->count);
- if (unlikely(oldcount & RWSEM_WRITER_MASK)) {
- /*
- * When we've been waiting "too" long (for writers
- * to give up the lock), request a HANDOFF to
- * force the issue.
- */
- if (!(oldcount & RWSEM_FLAG_HANDOFF) &&
- time_after(jiffies, waiter->timeout)) {
- adjustment -= RWSEM_FLAG_HANDOFF;
- lockevent_inc(rwsem_rlock_handoff);
- }
- atomic_long_add(-adjustment, &sem->count);
- return;
- }
- /*
- * Set it to reader-owned to give spinners an early
- * indication that readers now have the lock.
- * The reader nonspinnable bit seen at slowpath entry of
- * the reader is copied over.
- */
- owner = waiter->task;
- if (waiter->last_rowner & RWSEM_RD_NONSPINNABLE) {
- owner = (void *)((unsigned long)owner | RWSEM_RD_NONSPINNABLE);
- lockevent_inc(rwsem_opt_norspin);
- }
- __rwsem_set_reader_owned(sem, owner);
- }
- /*
- * Grant up to MAX_READERS_WAKEUP read locks to all the readers in the
- * queue. We know that the woken will be at least 1 as we accounted
- * for above. Note we increment the 'active part' of the count by the
- * number of readers before waking any processes up.
- *
- * This is an adaptation of the phase-fair R/W locks where at the
- * reader phase (first waiter is a reader), all readers are eligible
- * to acquire the lock at the same time irrespective of their order
- * in the queue. The writers acquire the lock according to their
- * order in the queue.
- *
- * We have to do wakeup in 2 passes to prevent the possibility that
- * the reader count may be decremented before it is incremented. It
- * is because the to-be-woken waiter may not have slept yet. So it
- * may see waiter->task got cleared, finish its critical section and
- * do an unlock before the reader count increment.
- *
- * 1) Collect the read-waiters in a separate list, count them and
- * fully increment the reader count in rwsem.
- * 2) For each waiters in the new list, clear waiter->task and
- * put them into wake_q to be woken up later.
- */
- INIT_LIST_HEAD(&wlist);
- list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {
- if (waiter->type == RWSEM_WAITING_FOR_WRITE)
- continue;
- woken++;
- list_move_tail(&waiter->list, &wlist);
- trace_android_vh_rwsem_mark_wake_readers(sem, waiter);
- /*
- * Limit # of readers that can be woken up per wakeup call.
- */
- if (woken >= MAX_READERS_WAKEUP)
- break;
- }
- adjustment = woken * RWSEM_READER_BIAS - adjustment;
- lockevent_cond_inc(rwsem_wake_reader, woken);
- if (list_empty(&sem->wait_list)) {
- /* hit end of list above */
- adjustment -= RWSEM_FLAG_WAITERS;
- }
- /*
- * When we've woken a reader, we no longer need to force writers
- * to give up the lock and we can clear HANDOFF.
- */
- if (woken && (atomic_long_read(&sem->count) & RWSEM_FLAG_HANDOFF))
- adjustment -= RWSEM_FLAG_HANDOFF;
- if (adjustment)
- atomic_long_add(adjustment, &sem->count);
- /* 2nd pass */
- list_for_each_entry_safe(waiter, tmp, &wlist, list) {
- struct task_struct *tsk;
- tsk = waiter->task;
- get_task_struct(tsk);
- /*
- * Ensure calling get_task_struct() before setting the reader
- * waiter to nil such that rwsem_down_read_slowpath() cannot
- * race with do_exit() by always holding a reference count
- * to the task to wakeup.
- */
- smp_store_release(&waiter->task, NULL);
- /*
- * Ensure issuing the wakeup (either by us or someone else)
- * after setting the reader waiter to nil.
- */
- wake_q_add_safe(wake_q, tsk);
- }
- }
- /*
- * This function must be called with the sem->wait_lock held to prevent
- * race conditions between checking the rwsem wait list and setting the
- * sem->count accordingly.
- *
- * If wstate is WRITER_HANDOFF, it will make sure that either the handoff
- * bit is set or the lock is acquired with handoff bit cleared.
- */
- static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
- enum writer_wait_state wstate)
- {
- long count, new;
- lockdep_assert_held(&sem->wait_lock);
- count = atomic_long_read(&sem->count);
- do {
- bool has_handoff = !!(count & RWSEM_FLAG_HANDOFF);
- if (has_handoff && wstate == WRITER_NOT_FIRST)
- return false;
- new = count;
- if (count & RWSEM_LOCK_MASK) {
- if (has_handoff || (wstate != WRITER_HANDOFF))
- return false;
- new |= RWSEM_FLAG_HANDOFF;
- } else {
- new |= RWSEM_WRITER_LOCKED;
- new &= ~RWSEM_FLAG_HANDOFF;
- if (list_is_singular(&sem->wait_list))
- new &= ~RWSEM_FLAG_WAITERS;
- }
- } while (!atomic_long_try_cmpxchg_acquire(&sem->count, &count, new));
- /*
- * We have either acquired the lock with handoff bit cleared or
- * set the handoff bit.
- */
- if (new & RWSEM_FLAG_HANDOFF)
- return false;
- rwsem_set_owner(sem);
- return true;
- }
- #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
- /*
- * Try to acquire read lock before the reader is put on wait queue.
- * Lock acquisition isn't allowed if the rwsem is locked or a writer handoff
- * is ongoing.
- */
- static inline bool rwsem_try_read_lock_unqueued(struct rw_semaphore *sem)
- {
- long count = atomic_long_read(&sem->count);
- if (count & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))
- return false;
- count = atomic_long_fetch_add_acquire(RWSEM_READER_BIAS, &sem->count);
- if (!(count & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
- rwsem_set_reader_owned(sem);
- lockevent_inc(rwsem_opt_rlock);
- return true;
- }
- /* Back out the change */
- atomic_long_add(-RWSEM_READER_BIAS, &sem->count);
- return false;
- }
- /*
- * Try to acquire write lock before the writer has been put on wait queue.
- */
- static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
- {
- long count = atomic_long_read(&sem->count);
- while (!(count & (RWSEM_LOCK_MASK|RWSEM_FLAG_HANDOFF))) {
- if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
- count | RWSEM_WRITER_LOCKED)) {
- rwsem_set_owner(sem);
- lockevent_inc(rwsem_opt_wlock);
- return true;
- }
- }
- return false;
- }
- static inline bool owner_on_cpu(struct task_struct *owner)
- {
- /*
- * As lock holder preemption issue, we both skip spinning if
- * task is not on cpu or its cpu is preempted
- */
- return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
- }
- static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
- unsigned long nonspinnable)
- {
- struct task_struct *owner;
- unsigned long flags;
- bool ret = true;
- if (need_resched()) {
- lockevent_inc(rwsem_opt_fail);
- return false;
- }
- preempt_disable();
- rcu_read_lock();
- owner = rwsem_owner_flags(sem, &flags);
- /*
- * Don't check the read-owner as the entry may be stale.
- */
- if ((flags & nonspinnable) ||
- (owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner)))
- ret = false;
- rcu_read_unlock();
- preempt_enable();
- lockevent_cond_inc(rwsem_opt_fail, !ret);
- return ret;
- }
- /*
- * The rwsem_spin_on_owner() function returns the folowing 4 values
- * depending on the lock owner state.
- * OWNER_NULL : owner is currently NULL
- * OWNER_WRITER: when owner changes and is a writer
- * OWNER_READER: when owner changes and the new owner may be a reader.
- * OWNER_NONSPINNABLE:
- * when optimistic spinning has to stop because either the
- * owner stops running, is unknown, or its timeslice has
- * been used up.
- */
- enum owner_state {
- OWNER_NULL = 1 << 0,
- OWNER_WRITER = 1 << 1,
- OWNER_READER = 1 << 2,
- OWNER_NONSPINNABLE = 1 << 3,
- };
- #define OWNER_SPINNABLE (OWNER_NULL | OWNER_WRITER | OWNER_READER)
- static inline enum owner_state
- rwsem_owner_state(struct task_struct *owner, unsigned long flags, unsigned long nonspinnable)
- {
- if (flags & nonspinnable)
- return OWNER_NONSPINNABLE;
- if (flags & RWSEM_READER_OWNED)
- return OWNER_READER;
- return owner ? OWNER_WRITER : OWNER_NULL;
- }
- static noinline enum owner_state
- rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
- {
- struct task_struct *new, *owner;
- unsigned long flags, new_flags;
- enum owner_state state;
- owner = rwsem_owner_flags(sem, &flags);
- state = rwsem_owner_state(owner, flags, nonspinnable);
- if (state != OWNER_WRITER)
- return state;
- rcu_read_lock();
- for (;;) {
- /*
- * When a waiting writer set the handoff flag, it may spin
- * on the owner as well. Once that writer acquires the lock,
- * we can spin on it. So we don't need to quit even when the
- * handoff bit is set.
- */
- new = rwsem_owner_flags(sem, &new_flags);
- if ((new != owner) || (new_flags != flags)) {
- state = rwsem_owner_state(new, new_flags, nonspinnable);
- break;
- }
- /*
- * Ensure we emit the owner->on_cpu, dereference _after_
- * checking sem->owner still matches owner, if that fails,
- * owner might point to free()d memory, if it still matches,
- * the rcu_read_lock() ensures the memory stays valid.
- */
- barrier();
- if (need_resched() || !owner_on_cpu(owner)) {
- state = OWNER_NONSPINNABLE;
- break;
- }
- cpu_relax();
- }
- rcu_read_unlock();
- return state;
- }
- /*
- * Calculate reader-owned rwsem spinning threshold for writer
- *
- * The more readers own the rwsem, the longer it will take for them to
- * wind down and free the rwsem. So the empirical formula used to
- * determine the actual spinning time limit here is:
- *
- * Spinning threshold = (10 + nr_readers/2)us
- *
- * The limit is capped to a maximum of 25us (30 readers). This is just
- * a heuristic and is subjected to change in the future.
- */
- static inline u64 rwsem_rspin_threshold(struct rw_semaphore *sem)
- {
- long count = atomic_long_read(&sem->count);
- int readers = count >> RWSEM_READER_SHIFT;
- u64 delta;
- if (readers > 30)
- readers = 30;
- delta = (20 + readers) * NSEC_PER_USEC / 2;
- return sched_clock() + delta;
- }
- static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
- {
- bool taken = false;
- int prev_owner_state = OWNER_NULL;
- int loop = 0;
- u64 rspin_threshold = 0;
- unsigned long nonspinnable = wlock ? RWSEM_WR_NONSPINNABLE
- : RWSEM_RD_NONSPINNABLE;
- preempt_disable();
- /* sem->wait_lock should not be held when doing optimistic spinning */
- if (!osq_lock(&sem->osq))
- goto done;
- /*
- * Optimistically spin on the owner field and attempt to acquire the
- * lock whenever the owner changes. Spinning will be stopped when:
- * 1) the owning writer isn't running; or
- * 2) readers own the lock and spinning time has exceeded limit.
- */
- for (;;) {
- enum owner_state owner_state;
- owner_state = rwsem_spin_on_owner(sem, nonspinnable);
- if (!(owner_state & OWNER_SPINNABLE))
- break;
- /*
- * Try to acquire the lock
- */
- taken = wlock ? rwsem_try_write_lock_unqueued(sem)
- : rwsem_try_read_lock_unqueued(sem);
- if (taken)
- break;
- /*
- * Time-based reader-owned rwsem optimistic spinning
- */
- if (wlock && (owner_state == OWNER_READER)) {
- /*
- * Re-initialize rspin_threshold every time when
- * the owner state changes from non-reader to reader.
- * This allows a writer to steal the lock in between
- * 2 reader phases and have the threshold reset at
- * the beginning of the 2nd reader phase.
- */
- if (prev_owner_state != OWNER_READER) {
- if (rwsem_test_oflags(sem, nonspinnable))
- break;
- rspin_threshold = rwsem_rspin_threshold(sem);
- loop = 0;
- }
- /*
- * Check time threshold once every 16 iterations to
- * avoid calling sched_clock() too frequently so
- * as to reduce the average latency between the times
- * when the lock becomes free and when the spinner
- * is ready to do a trylock.
- */
- else if (!(++loop & 0xf) && (sched_clock() > rspin_threshold)) {
- rwsem_set_nonspinnable(sem);
- lockevent_inc(rwsem_opt_nospin);
- break;
- }
- }
- /*
- * An RT task cannot do optimistic spinning if it cannot
- * be sure the lock holder is running or live-lock may
- * happen if the current task and the lock holder happen
- * to run in the same CPU. However, aborting optimistic
- * spinning while a NULL owner is detected may miss some
- * opportunity where spinning can continue without causing
- * problem.
- *
- * There are 2 possible cases where an RT task may be able
- * to continue spinning.
- *
- * 1) The lock owner is in the process of releasing the
- * lock, sem->owner is cleared but the lock has not
- * been released yet.
- * 2) The lock was free and owner cleared, but another
- * task just comes in and acquire the lock before
- * we try to get it. The new owner may be a spinnable
- * writer.
- *
- * To take advantage of two scenarios listed agove, the RT
- * task is made to retry one more time to see if it can
- * acquire the lock or continue spinning on the new owning
- * writer. Of course, if the time lag is long enough or the
- * new owner is not a writer or spinnable, the RT task will
- * quit spinning.
- *
- * If the owner is a writer, the need_resched() check is
- * done inside rwsem_spin_on_owner(). If the owner is not
- * a writer, need_resched() check needs to be done here.
- */
- if (owner_state != OWNER_WRITER) {
- if (need_resched())
- break;
- if (rt_task(current) &&
- (prev_owner_state != OWNER_WRITER))
- break;
- }
- prev_owner_state = owner_state;
- /*
- * The cpu_relax() call is a compiler barrier which forces
- * everything in this loop to be re-loaded. We don't need
- * memory barriers as we'll eventually observe the right
- * values at the cost of a few extra spins.
- */
- cpu_relax();
- }
- osq_unlock(&sem->osq);
- done:
- preempt_enable();
- lockevent_cond_inc(rwsem_opt_fail, !taken);
- return taken;
- }
- /*
- * Clear the owner's RWSEM_WR_NONSPINNABLE bit if it is set. This should
- * only be called when the reader count reaches 0.
- *
- * This give writers better chance to acquire the rwsem first before
- * readers when the rwsem was being held by readers for a relatively long
- * period of time. Race can happen that an optimistic spinner may have
- * just stolen the rwsem and set the owner, but just clearing the
- * RWSEM_WR_NONSPINNABLE bit will do no harm anyway.
- */
- static inline void clear_wr_nonspinnable(struct rw_semaphore *sem)
- {
- if (rwsem_test_oflags(sem, RWSEM_WR_NONSPINNABLE))
- atomic_long_andnot(RWSEM_WR_NONSPINNABLE, &sem->owner);
- }
- /*
- * This function is called when the reader fails to acquire the lock via
- * optimistic spinning. In this case we will still attempt to do a trylock
- * when comparing the rwsem state right now with the state when entering
- * the slowpath indicates that the reader is still in a valid reader phase.
- * This happens when the following conditions are true:
- *
- * 1) The lock is currently reader owned, and
- * 2) The lock is previously not reader-owned or the last read owner changes.
- *
- * In the former case, we have transitioned from a writer phase to a
- * reader-phase while spinning. In the latter case, it means the reader
- * phase hasn't ended when we entered the optimistic spinning loop. In
- * both cases, the reader is eligible to acquire the lock. This is the
- * secondary path where a read lock is acquired optimistically.
- *
- * The reader non-spinnable bit wasn't set at time of entry or it will
- * not be here at all.
- */
- static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
- unsigned long last_rowner)
- {
- unsigned long owner = atomic_long_read(&sem->owner);
- if (!(owner & RWSEM_READER_OWNED))
- return false;
- if (((owner ^ last_rowner) & ~RWSEM_OWNER_FLAGS_MASK) &&
- rwsem_try_read_lock_unqueued(sem)) {
- lockevent_inc(rwsem_opt_rlock2);
- lockevent_add(rwsem_opt_fail, -1);
- return true;
- }
- return false;
- }
- #else
- static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
- unsigned long nonspinnable)
- {
- return false;
- }
- static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
- {
- return false;
- }
- static inline void clear_wr_nonspinnable(struct rw_semaphore *sem) { }
- static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
- unsigned long last_rowner)
- {
- return false;
- }
- static inline int
- rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
- {
- return 0;
- }
- #define OWNER_NULL 1
- #endif
- /*
- * Wait for the read lock to be granted
- */
- static struct rw_semaphore __sched *
- rwsem_down_read_slowpath(struct rw_semaphore *sem, int state)
- {
- long count, adjustment = -RWSEM_READER_BIAS;
- struct rwsem_waiter waiter;
- DEFINE_WAKE_Q(wake_q);
- bool wake = false;
- bool already_on_list = false;
- /*
- * Save the current read-owner of rwsem, if available, and the
- * reader nonspinnable bit.
- */
- waiter.last_rowner = atomic_long_read(&sem->owner);
- if (!(waiter.last_rowner & RWSEM_READER_OWNED))
- waiter.last_rowner &= RWSEM_RD_NONSPINNABLE;
- if (!rwsem_can_spin_on_owner(sem, RWSEM_RD_NONSPINNABLE))
- goto queue;
- /*
- * Undo read bias from down_read() and do optimistic spinning.
- */
- atomic_long_add(-RWSEM_READER_BIAS, &sem->count);
- adjustment = 0;
- if (rwsem_optimistic_spin(sem, false)) {
- /* rwsem_optimistic_spin() implies ACQUIRE on success */
- /*
- * Wake up other readers in the wait list if the front
- * waiter is a reader.
- */
- if ((atomic_long_read(&sem->count) & RWSEM_FLAG_WAITERS)) {
- raw_spin_lock_irq(&sem->wait_lock);
- if (!list_empty(&sem->wait_list))
- rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED,
- &wake_q);
- raw_spin_unlock_irq(&sem->wait_lock);
- wake_up_q(&wake_q);
- }
- return sem;
- } else if (rwsem_reader_phase_trylock(sem, waiter.last_rowner)) {
- /* rwsem_reader_phase_trylock() implies ACQUIRE on success */
- return sem;
- }
- queue:
- waiter.task = current;
- waiter.type = RWSEM_WAITING_FOR_READ;
- waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
- raw_spin_lock_irq(&sem->wait_lock);
- if (list_empty(&sem->wait_list)) {
- /*
- * In case the wait queue is empty and the lock isn't owned
- * by a writer or has the handoff bit set, this reader can
- * exit the slowpath and return immediately as its
- * RWSEM_READER_BIAS has already been set in the count.
- */
- if (adjustment && !(atomic_long_read(&sem->count) &
- (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
- /* Provide lock ACQUIRE */
- smp_acquire__after_ctrl_dep();
- raw_spin_unlock_irq(&sem->wait_lock);
- rwsem_set_reader_owned(sem);
- lockevent_inc(rwsem_rlock_fast);
- return sem;
- }
- adjustment += RWSEM_FLAG_WAITERS;
- }
- trace_android_vh_alter_rwsem_list_add(
- &waiter,
- sem, &already_on_list);
- if (!already_on_list)
- list_add_tail(&waiter.list, &sem->wait_list);
- /* we're now waiting on the lock, but no longer actively locking */
- if (adjustment)
- count = atomic_long_add_return(adjustment, &sem->count);
- else
- count = atomic_long_read(&sem->count);
- /*
- * If there are no active locks, wake the front queued process(es).
- *
- * If there are no writers and we are first in the queue,
- * wake our own waiter to join the existing active readers !
- */
- if (!(count & RWSEM_LOCK_MASK)) {
- clear_wr_nonspinnable(sem);
- wake = true;
- }
- if (wake || (!(count & RWSEM_WRITER_MASK) &&
- (adjustment & RWSEM_FLAG_WAITERS)))
- rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
- trace_android_vh_rwsem_wake(sem);
- raw_spin_unlock_irq(&sem->wait_lock);
- wake_up_q(&wake_q);
- /* wait to be given the lock */
- trace_android_vh_rwsem_read_wait_start(sem);
- for (;;) {
- set_current_state(state);
- if (!smp_load_acquire(&waiter.task)) {
- /* Matches rwsem_mark_wake()'s smp_store_release(). */
- break;
- }
- if (signal_pending_state(state, current)) {
- raw_spin_lock_irq(&sem->wait_lock);
- if (waiter.task)
- goto out_nolock;
- raw_spin_unlock_irq(&sem->wait_lock);
- /* Ordered by sem->wait_lock against rwsem_mark_wake(). */
- break;
- }
- schedule();
- lockevent_inc(rwsem_sleep_reader);
- }
- __set_current_state(TASK_RUNNING);
- trace_android_vh_rwsem_read_wait_finish(sem);
- lockevent_inc(rwsem_rlock);
- return sem;
- out_nolock:
- list_del(&waiter.list);
- if (list_empty(&sem->wait_list)) {
- atomic_long_andnot(RWSEM_FLAG_WAITERS|RWSEM_FLAG_HANDOFF,
- &sem->count);
- }
- raw_spin_unlock_irq(&sem->wait_lock);
- __set_current_state(TASK_RUNNING);
- trace_android_vh_rwsem_read_wait_finish(sem);
- lockevent_inc(rwsem_rlock_fail);
- return ERR_PTR(-EINTR);
- }
- /*
- * This function is called by the a write lock owner. So the owner value
- * won't get changed by others.
- */
- static inline void rwsem_disable_reader_optspin(struct rw_semaphore *sem,
- bool disable)
- {
- if (unlikely(disable)) {
- atomic_long_or(RWSEM_RD_NONSPINNABLE, &sem->owner);
- lockevent_inc(rwsem_opt_norspin);
- }
- }
- /*
- * Wait until we successfully acquire the write lock
- */
- static struct rw_semaphore *
- rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
- {
- long count;
- bool disable_rspin;
- enum writer_wait_state wstate;
- struct rwsem_waiter waiter;
- struct rw_semaphore *ret = sem;
- DEFINE_WAKE_Q(wake_q);
- bool already_on_list = false;
- /* do optimistic spinning and steal lock if possible */
- if (rwsem_can_spin_on_owner(sem, RWSEM_WR_NONSPINNABLE) &&
- rwsem_optimistic_spin(sem, true)) {
- /* rwsem_optimistic_spin() implies ACQUIRE on success */
- return sem;
- }
- /*
- * Disable reader optimistic spinning for this rwsem after
- * acquiring the write lock when the setting of the nonspinnable
- * bits are observed.
- */
- disable_rspin = atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE;
- /*
- * Optimistic spinning failed, proceed to the slowpath
- * and block until we can acquire the sem.
- */
- waiter.task = current;
- waiter.type = RWSEM_WAITING_FOR_WRITE;
- waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
- raw_spin_lock_irq(&sem->wait_lock);
- /* account for this before adding a new element to the list */
- wstate = list_empty(&sem->wait_list) ? WRITER_FIRST : WRITER_NOT_FIRST;
- trace_android_vh_alter_rwsem_list_add(
- &waiter,
- sem, &already_on_list);
- if (!already_on_list)
- list_add_tail(&waiter.list, &sem->wait_list);
- /* we're now waiting on the lock */
- if (wstate == WRITER_NOT_FIRST) {
- count = atomic_long_read(&sem->count);
- /*
- * If there were already threads queued before us and:
- * 1) there are no active locks, wake the front
- * queued process(es) as the handoff bit might be set.
- * 2) there are no active writers and some readers, the lock
- * must be read owned; so we try to wake any read lock
- * waiters that were queued ahead of us.
- */
- if (count & RWSEM_WRITER_MASK)
- goto wait;
- rwsem_mark_wake(sem, (count & RWSEM_READER_MASK)
- ? RWSEM_WAKE_READERS
- : RWSEM_WAKE_ANY, &wake_q);
- if (!wake_q_empty(&wake_q)) {
- /*
- * We want to minimize wait_lock hold time especially
- * when a large number of readers are to be woken up.
- */
- raw_spin_unlock_irq(&sem->wait_lock);
- wake_up_q(&wake_q);
- wake_q_init(&wake_q); /* Used again, reinit */
- raw_spin_lock_irq(&sem->wait_lock);
- }
- } else {
- atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count);
- }
- wait:
- trace_android_vh_rwsem_wake(sem);
- /* wait until we successfully acquire the lock */
- trace_android_vh_rwsem_write_wait_start(sem);
- set_current_state(state);
- for (;;) {
- if (rwsem_try_write_lock(sem, wstate)) {
- /* rwsem_try_write_lock() implies ACQUIRE on success */
- break;
- }
- raw_spin_unlock_irq(&sem->wait_lock);
- /*
- * After setting the handoff bit and failing to acquire
- * the lock, attempt to spin on owner to accelerate lock
- * transfer. If the previous owner is a on-cpu writer and it
- * has just released the lock, OWNER_NULL will be returned.
- * In this case, we attempt to acquire the lock again
- * without sleeping.
- */
- if (wstate == WRITER_HANDOFF &&
- rwsem_spin_on_owner(sem, RWSEM_NONSPINNABLE) == OWNER_NULL)
- goto trylock_again;
- /* Block until there are no active lockers. */
- for (;;) {
- if (signal_pending_state(state, current))
- goto out_nolock;
- schedule();
- lockevent_inc(rwsem_sleep_writer);
- set_current_state(state);
- /*
- * If HANDOFF bit is set, unconditionally do
- * a trylock.
- */
- if (wstate == WRITER_HANDOFF)
- break;
- if ((wstate == WRITER_NOT_FIRST) &&
- (rwsem_first_waiter(sem) == &waiter))
- wstate = WRITER_FIRST;
- count = atomic_long_read(&sem->count);
- if (!(count & RWSEM_LOCK_MASK))
- break;
- /*
- * The setting of the handoff bit is deferred
- * until rwsem_try_write_lock() is called.
- */
- if ((wstate == WRITER_FIRST) && (rt_task(current) ||
- time_after(jiffies, waiter.timeout))) {
- wstate = WRITER_HANDOFF;
- lockevent_inc(rwsem_wlock_handoff);
- break;
- }
- }
- trylock_again:
- raw_spin_lock_irq(&sem->wait_lock);
- }
- __set_current_state(TASK_RUNNING);
- trace_android_vh_rwsem_write_wait_finish(sem);
- list_del(&waiter.list);
- rwsem_disable_reader_optspin(sem, disable_rspin);
- raw_spin_unlock_irq(&sem->wait_lock);
- lockevent_inc(rwsem_wlock);
- return ret;
- out_nolock:
- __set_current_state(TASK_RUNNING);
- trace_android_vh_rwsem_write_wait_finish(sem);
- raw_spin_lock_irq(&sem->wait_lock);
- list_del(&waiter.list);
- if (unlikely(wstate == WRITER_HANDOFF))
- atomic_long_andnot(RWSEM_FLAG_HANDOFF, &sem->count);
- if (list_empty(&sem->wait_list))
- atomic_long_andnot(RWSEM_FLAG_WAITERS, &sem->count);
- else
- rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
- raw_spin_unlock_irq(&sem->wait_lock);
- wake_up_q(&wake_q);
- lockevent_inc(rwsem_wlock_fail);
- return ERR_PTR(-EINTR);
- }
- /*
- * handle waking up a waiter on the semaphore
- * - up_read/up_write has decremented the active part of count if we come here
- */
- static struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem, long count)
- {
- unsigned long flags;
- DEFINE_WAKE_Q(wake_q);
- raw_spin_lock_irqsave(&sem->wait_lock, flags);
- if (!list_empty(&sem->wait_list))
- rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
- trace_android_vh_rwsem_wake_finish(sem);
- raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
- wake_up_q(&wake_q);
- return sem;
- }
- /*
- * downgrade a write lock into a read lock
- * - caller incremented waiting part of count and discovered it still negative
- * - just wake up any readers at the front of the queue
- */
- static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
- {
- unsigned long flags;
- DEFINE_WAKE_Q(wake_q);
- raw_spin_lock_irqsave(&sem->wait_lock, flags);
- if (!list_empty(&sem->wait_list))
- rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);
- raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
- wake_up_q(&wake_q);
- return sem;
- }
- /*
- * lock for reading
- */
- static inline void __down_read(struct rw_semaphore *sem)
- {
- if (!rwsem_read_trylock(sem)) {
- rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE);
- DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
- } else {
- rwsem_set_reader_owned(sem);
- }
- }
- static inline int __down_read_interruptible(struct rw_semaphore *sem)
- {
- if (!rwsem_read_trylock(sem)) {
- if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_INTERRUPTIBLE)))
- return -EINTR;
- DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
- } else {
- rwsem_set_reader_owned(sem);
- }
- return 0;
- }
- static inline int __down_read_killable(struct rw_semaphore *sem)
- {
- if (!rwsem_read_trylock(sem)) {
- if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE)))
- return -EINTR;
- DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
- } else {
- rwsem_set_reader_owned(sem);
- }
- return 0;
- }
- static inline int __down_read_trylock(struct rw_semaphore *sem)
- {
- long tmp;
- DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
- /*
- * Optimize for the case when the rwsem is not locked at all.
- */
- tmp = RWSEM_UNLOCKED_VALUE;
- do {
- if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
- tmp + RWSEM_READER_BIAS)) {
- rwsem_set_reader_owned(sem);
- return 1;
- }
- } while (!(tmp & RWSEM_READ_FAILED_MASK));
- return 0;
- }
- /*
- * lock for writing
- */
- static inline void __down_write(struct rw_semaphore *sem)
- {
- long tmp = RWSEM_UNLOCKED_VALUE;
- if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
- RWSEM_WRITER_LOCKED)))
- rwsem_down_write_slowpath(sem, TASK_UNINTERRUPTIBLE);
- else
- rwsem_set_owner(sem);
- }
- static inline int __down_write_killable(struct rw_semaphore *sem)
- {
- long tmp = RWSEM_UNLOCKED_VALUE;
- if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
- RWSEM_WRITER_LOCKED))) {
- if (IS_ERR(rwsem_down_write_slowpath(sem, TASK_KILLABLE)))
- return -EINTR;
- } else {
- rwsem_set_owner(sem);
- }
- return 0;
- }
- static inline int __down_write_trylock(struct rw_semaphore *sem)
- {
- long tmp;
- DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
- tmp = RWSEM_UNLOCKED_VALUE;
- if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
- RWSEM_WRITER_LOCKED)) {
- rwsem_set_owner(sem);
- return true;
- }
- return false;
- }
- /*
- * unlock after reading
- */
- static inline void __up_read(struct rw_semaphore *sem)
- {
- long tmp;
- DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
- DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
- rwsem_clear_reader_owned(sem);
- tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);
- DEBUG_RWSEMS_WARN_ON(tmp < 0, sem);
- if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) ==
- RWSEM_FLAG_WAITERS)) {
- clear_wr_nonspinnable(sem);
- rwsem_wake(sem, tmp);
- }
- trace_android_vh_rwsem_up_read_end(sem);
- }
- /*
- * unlock after writing
- */
- static inline void __up_write(struct rw_semaphore *sem)
- {
- long tmp;
- DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
- /*
- * sem->owner may differ from current if the ownership is transferred
- * to an anonymous writer by setting the RWSEM_NONSPINNABLE bits.
- */
- DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) &&
- !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE), sem);
- rwsem_clear_owner(sem);
- tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count);
- if (unlikely(tmp & RWSEM_FLAG_WAITERS))
- rwsem_wake(sem, tmp);
- trace_android_vh_rwsem_up_write_end(sem);
- }
- /*
- * downgrade write lock to read lock
- */
- static inline void __downgrade_write(struct rw_semaphore *sem)
- {
- long tmp;
- /*
- * When downgrading from exclusive to shared ownership,
- * anything inside the write-locked region cannot leak
- * into the read side. In contrast, anything in the
- * read-locked region is ok to be re-ordered into the
- * write side. As such, rely on RELEASE semantics.
- */
- DEBUG_RWSEMS_WARN_ON(rwsem_owner(sem) != current, sem);
- tmp = atomic_long_fetch_add_release(
- -RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count);
- rwsem_set_reader_owned(sem);
- if (tmp & RWSEM_FLAG_WAITERS)
- rwsem_downgrade_wake(sem);
- }
- /*
- * lock for reading
- */
- void __sched down_read(struct rw_semaphore *sem)
- {
- might_sleep();
- rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
- LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
- }
- EXPORT_SYMBOL(down_read);
- int __sched down_read_interruptible(struct rw_semaphore *sem)
- {
- might_sleep();
- rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
- if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) {
- rwsem_release(&sem->dep_map, _RET_IP_);
- return -EINTR;
- }
- return 0;
- }
- EXPORT_SYMBOL(down_read_interruptible);
- int __sched down_read_killable(struct rw_semaphore *sem)
- {
- might_sleep();
- rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
- if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
- rwsem_release(&sem->dep_map, _RET_IP_);
- return -EINTR;
- }
- return 0;
- }
- EXPORT_SYMBOL(down_read_killable);
- /*
- * trylock for reading -- returns 1 if successful, 0 if contention
- */
- int down_read_trylock(struct rw_semaphore *sem)
- {
- int ret = __down_read_trylock(sem);
- if (ret == 1)
- rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
- return ret;
- }
- EXPORT_SYMBOL(down_read_trylock);
- /*
- * lock for writing
- */
- void __sched down_write(struct rw_semaphore *sem)
- {
- might_sleep();
- rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
- LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
- }
- EXPORT_SYMBOL(down_write);
- /*
- * lock for writing
- */
- int __sched down_write_killable(struct rw_semaphore *sem)
- {
- might_sleep();
- rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
- if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
- __down_write_killable)) {
- rwsem_release(&sem->dep_map, _RET_IP_);
- return -EINTR;
- }
- return 0;
- }
- EXPORT_SYMBOL(down_write_killable);
- /*
- * trylock for writing -- returns 1 if successful, 0 if contention
- */
- int down_write_trylock(struct rw_semaphore *sem)
- {
- int ret = __down_write_trylock(sem);
- if (ret == 1)
- rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
- return ret;
- }
- EXPORT_SYMBOL(down_write_trylock);
- /*
- * release a read lock
- */
- void up_read(struct rw_semaphore *sem)
- {
- rwsem_release(&sem->dep_map, _RET_IP_);
- __up_read(sem);
- }
- EXPORT_SYMBOL(up_read);
- /*
- * release a write lock
- */
- void up_write(struct rw_semaphore *sem)
- {
- rwsem_release(&sem->dep_map, _RET_IP_);
- trace_android_vh_rwsem_write_finished(sem);
- __up_write(sem);
- }
- EXPORT_SYMBOL(up_write);
- /*
- * downgrade write lock to read lock
- */
- void downgrade_write(struct rw_semaphore *sem)
- {
- lock_downgrade(&sem->dep_map, _RET_IP_);
- trace_android_vh_rwsem_write_finished(sem);
- __downgrade_write(sem);
- }
- EXPORT_SYMBOL(downgrade_write);
- #ifdef CONFIG_DEBUG_LOCK_ALLOC
- void down_read_nested(struct rw_semaphore *sem, int subclass)
- {
- might_sleep();
- rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
- LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
- }
- EXPORT_SYMBOL(down_read_nested);
- int down_read_killable_nested(struct rw_semaphore *sem, int subclass)
- {
- might_sleep();
- rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
- if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
- rwsem_release(&sem->dep_map, _RET_IP_);
- return -EINTR;
- }
- return 0;
- }
- EXPORT_SYMBOL(down_read_killable_nested);
- void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
- {
- might_sleep();
- rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
- LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
- }
- EXPORT_SYMBOL(_down_write_nest_lock);
- void down_read_non_owner(struct rw_semaphore *sem)
- {
- might_sleep();
- __down_read(sem);
- __rwsem_set_reader_owned(sem, NULL);
- }
- EXPORT_SYMBOL(down_read_non_owner);
- void down_write_nested(struct rw_semaphore *sem, int subclass)
- {
- might_sleep();
- rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
- LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
- }
- EXPORT_SYMBOL(down_write_nested);
- int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
- {
- might_sleep();
- rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
- if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
- __down_write_killable)) {
- rwsem_release(&sem->dep_map, _RET_IP_);
- return -EINTR;
- }
- return 0;
- }
- EXPORT_SYMBOL(down_write_killable_nested);
- void up_read_non_owner(struct rw_semaphore *sem)
- {
- DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
- __up_read(sem);
- }
- EXPORT_SYMBOL(up_read_non_owner);
- #endif
|