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tty/ldsem, locking/rwsem: Add missing ACQUIRE to read_failed sleep loop

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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>
This commit is contained in:
Peter Zijlstra 2019-07-18 15:03:15 +02:00 committed by Ingo Molnar
parent 99143f82a2
commit 952041a863
1 changed files with 2 additions and 3 deletions
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5
drivers/tty/tty_ldsem.c
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@ -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;