From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will@kernel.org>
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Jan Stancek <jstancek@redhat.com>,
Waiman Long <longman@redhat.com>,
dbueso@suse.de, mingo@redhat.com, jade.alglave@arm.com,
paulmck@linux.vnet.ibm.com
Subject: [PATCH 4/4] rwsem: Add ACQUIRE comments
Date: Thu, 18 Jul 2019 15:49:58 +0200 [thread overview]
Message-ID: <20190718135206.228078863@infradead.org> (raw)
In-Reply-To: 20190718134954.496297975@infradead.org
Since we just reviewed read_slowpath for ACQUIRE correctness, add a
few coments to retain our findings.
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/locking/rwsem.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -1000,6 +1000,7 @@ rwsem_down_read_slowpath(struct rw_semap
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.
@@ -1014,6 +1015,7 @@ rwsem_down_read_slowpath(struct rw_semap
}
return sem;
} else if (rwsem_reader_phase_trylock(sem, waiter.last_rowner)) {
+ /* rwsem_reader_phase_trylock() implies ACQUIRE on success */
return sem;
}
@@ -1067,10 +1069,10 @@ rwsem_down_read_slowpath(struct rw_semap
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)) {
@@ -1078,6 +1080,7 @@ rwsem_down_read_slowpath(struct rw_semap
if (waiter.task)
goto out_nolock;
raw_spin_unlock_irq(&sem->wait_lock);
+ /* Ordered by sem->wait_lock against rwsem_mark_wake(). */
break;
}
schedule();
@@ -1087,6 +1090,7 @@ rwsem_down_read_slowpath(struct rw_semap
__set_current_state(TASK_RUNNING);
lockevent_inc(rwsem_rlock);
return sem;
+
out_nolock:
list_del(&waiter.list);
if (list_empty(&sem->wait_list)) {
@@ -1127,8 +1131,10 @@ rwsem_down_write_slowpath(struct rw_sema
/* 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
@@ -1188,9 +1194,11 @@ rwsem_down_write_slowpath(struct rw_sema
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);
next prev parent reply other threads:[~2019-07-18 13:53 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-18 13:49 [PATCH 0/4] Various rwsem ACQUIRE fixes Peter Zijlstra
2019-07-18 13:49 ` [PATCH 1/4] locking/rwsem: Add missing ACQUIRE to read_slowpath exit when queue is empty Peter Zijlstra
2019-07-19 8:49 ` Andrea Parri
2019-07-29 15:24 ` Peter Zijlstra
2019-07-18 13:49 ` [PATCH 2/4] rwsem: Add missing ACQUIRE to read_slowpath sleep loop Peter Zijlstra
2019-07-18 17:13 ` Waiman Long
2019-07-18 13:49 ` [PATCH 3/4] tty/ldsem: Add missing ACQUIRE to read_failed " Peter Zijlstra
2019-07-18 13:49 ` Peter Zijlstra [this message]
2019-07-29 15:18 ` [PATCH 0/4] Various rwsem ACQUIRE fixes Davidlohr Bueso
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