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authorPeter Zijlstra <peterz@infradead.org>2019-07-18 15:03:15 +0200
committerIngo Molnar <mingo@kernel.org>2019-07-25 15:39:24 +0200
commit952041a8639a7a3a73a2b6573cb8aa8518bc39f8 (patch)
treef2fe74978be7b45287b9f7275dbca20a3e2fcb56
parent99143f82a255e7f054bead8443462fae76dd829e (diff)
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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.c5
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;