[PATCH v2 04/35] watch_queue: use atomic find_bit() in post_one_notification()

Yury Norov
2023-12-03T19:33:26Z

post_one_notification() searches for a set bit in wqueue->notes_bitmap,
and after some housekeeping work clears it, firing a BUG() if someone
else cleared the bit in-between.

We can allocate the bit atomically with an atomic find_and_clear_bit(),
and remove the BUG() possibility entirely.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
kernel/watch_queue.c | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c
index 778b4056700f..07edd4a2b463 100644
--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -112,7 +112,7 @@ static bool post_one_notification(struct watch_queue *wqueue,
if (pipe_full(head, tail, pipe->ring_size))
goto lost;

- note = find_first_bit(wqueue->notes_bitmap, wqueue->nr_notes);
+ note = find_and_clear_bit(wqueue->notes_bitmap, wqueue->nr_notes);
if (note >= wqueue->nr_notes)
goto lost;

@@ -133,10 +133,6 @@ static bool post_one_notification(struct watch_queue *wqueue,
buf->flags = PIPE_BUF_FLAG_WHOLE;
smp_store_release(&pipe->head, head + 1); /* vs pipe_read() */

- if (!test_and_clear_bit(note, wqueue->notes_bitmap)) {
- spin_unlock_irq(&pipe->rd_wait.lock);
- BUG();
- }
wake_up_interruptible_sync_poll_locked(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
done = true;

--
2.40.1