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| author | Peter Zijlstra <peterz@infradead.org> | 2019-07-18 15:03:15 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2019-07-25 15:39:24 +0200 |
| commit | 952041a8639a7a3a73a2b6573cb8aa8518bc39f8 (patch) | |
| tree | f2fe74978be7b45287b9f7275dbca20a3e2fcb56 | |
| parent | 99143f82a255e7f054bead8443462fae76dd829e (diff) | |
| download | linux-952041a8639a7a3a73a2b6573cb8aa8518bc39f8.tar.gz linux-952041a8639a7a3a73a2b6573cb8aa8518bc39f8.tar.bz2 linux-952041a8639a7a3a73a2b6573cb8aa8518bc39f8.zip | |
tty/ldsem, locking/rwsem: Add missing ACQUIRE to read_failed sleep loop
While reviewing rwsem down_slowpath, Will noticed ldsem had a copy of
a bug we just found for rwsem.
X = 0;
CPU0 CPU1
rwsem_down_read()
for (;;) {
set_current_state(TASK_UNINTERRUPTIBLE);
X = 1;
rwsem_up_write();
rwsem_mark_wake()
atomic_long_add(adjustment, &sem->count);
smp_store_release(&waiter->task, NULL);
if (!waiter.task)
break;
...
}
r = X;
Allows 'r == 0'.
Reported-by: Will Deacon <will@kernel.org>
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 Hurley <peter@hurleysoftware.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 4898e640caf0 ("tty: Add timed, writer-prioritized rw semaphore")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
| -rw-r--r-- | drivers/tty/tty_ldsem.c | 5 |
1 files changed, 2 insertions, 3 deletions
diff --git a/drivers/tty/tty_ldsem.c b/drivers/tty/tty_ldsem.c index 717292c1c0df..60ff236a3d63 100644 --- a/drivers/tty/tty_ldsem.c +++ b/drivers/tty/tty_ldsem.c @@ -93,8 +93,7 @@ static void __ldsem_wake_readers(struct ld_semaphore *sem) list_for_each_entry_safe(waiter, next, &sem->read_wait, list) { tsk = waiter->task; - smp_mb(); - waiter->task = NULL; + smp_store_release(&waiter->task, NULL); wake_up_process(tsk); put_task_struct(tsk); } @@ -194,7 +193,7 @@ down_read_failed(struct ld_semaphore *sem, long count, long timeout) for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); - if (!waiter.task) + if (!smp_load_acquire(&waiter.task)) break; if (!timeout) break; |