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tty/ldsem, locking/rwsem: Add missing ACQUIRE to read_failed sleep loop
[ Upstream commit952041a863
] 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:4898e640ca
("tty: Add timed, writer-prioritized rw semaphore") Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
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1 changed files with 2 additions and 3 deletions
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@ -116,8 +116,7 @@ static void __ldsem_wake_readers(struct ld_semaphore *sem)
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list_for_each_entry_safe(waiter, next, &sem->read_wait, list) {
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tsk = waiter->task;
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smp_mb();
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waiter->task = NULL;
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smp_store_release(&waiter->task, NULL);
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wake_up_process(tsk);
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put_task_struct(tsk);
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}
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@ -217,7 +216,7 @@ down_read_failed(struct ld_semaphore *sem, long count, long timeout)
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for (;;) {
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set_current_state(TASK_UNINTERRUPTIBLE);
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if (!waiter.task)
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if (!smp_load_acquire(&waiter.task))
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break;
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if (!timeout)
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break;
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