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| author | Peter Zijlstra <peterz@infradead.org> | 2019-07-18 15:08:53 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2019-07-25 15:39:25 +0200 |
| commit | 6ffddfb9e1de21c3d0c0cfa4fe4a20dd3291a812 (patch) | |
| tree | 8515b223b81fbcdf12bceba14362cc0d31d1184d /kernel/locking | |
| parent | 952041a8639a7a3a73a2b6573cb8aa8518bc39f8 (diff) | |
| download | linux-6ffddfb9e1de21c3d0c0cfa4fe4a20dd3291a812.tar.bz2 | |
locking/rwsem: Add ACQUIRE comments
Since we just reviewed read_slowpath for ACQUIRE correctness, add a
few coments to retain our findings.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/rwsem.c | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 571938887cc8..bd0f0d05724c 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -1004,6 +1004,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, int state) 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. @@ -1018,6 +1019,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, int state) } return sem; } else if (rwsem_reader_phase_trylock(sem, waiter.last_rowner)) { + /* rwsem_reader_phase_trylock() implies ACQUIRE on success */ return sem; } @@ -1071,10 +1073,10 @@ queue: wake_up_q(&wake_q); /* wait to be given the lock */ - while (true) { + for (;;) { set_current_state(state); if (!smp_load_acquire(&waiter.task)) { - /* Orders against rwsem_mark_wake()'s smp_store_release() */ + /* Matches rwsem_mark_wake()'s smp_store_release(). */ break; } if (signal_pending_state(state, current)) { @@ -1082,6 +1084,7 @@ queue: if (waiter.task) goto out_nolock; raw_spin_unlock_irq(&sem->wait_lock); + /* Ordered by sem->wait_lock against rwsem_mark_wake(). */ break; } schedule(); @@ -1091,6 +1094,7 @@ queue: __set_current_state(TASK_RUNNING); lockevent_inc(rwsem_rlock); return sem; + out_nolock: list_del(&waiter.list); if (list_empty(&sem->wait_list)) { @@ -1131,8 +1135,10 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state) /* 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(sem, true)) { + /* rwsem_optimistic_spin() implies ACQUIRE on success */ return sem; + } /* * Disable reader optimistic spinning for this rwsem after @@ -1192,9 +1198,11 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state) wait: /* wait until we successfully acquire the lock */ set_current_state(state); - while (true) { - if (rwsem_try_write_lock(sem, wstate)) + for (;;) { + if (rwsem_try_write_lock(sem, wstate)) { + /* rwsem_try_write_lock() implies ACQUIRE on success */ break; + } raw_spin_unlock_irq(&sem->wait_lock); |