Commit 0d7bae69 authored Apr 19, 2019 by Stefan Bühler Committed by Jens Axboe Apr 22, 2019

io_uring: fix race condition when sq threads goes sleeping



Reading the SQ tail needs to come after setting IORING_SQ_NEED_WAKEUP in
flags; there is no cheap barrier for ordering a store before a load, a
full memory barrier is required.

Userspace needs a full memory barrier between updating SQ tail and
checking for the IORING_SQ_NEED_WAKEUP too.

Signed-off-by: Stefan Bühler <source@stbuehler.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent e523a29c

fs/io_uring.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -1865,7 +1865,8 @@ static int io_sq_thread(void *data)

		/* Tell userspace we may need a wakeup call */
		ctx->sq_ring->flags \|= IORING_SQ_NEED_WAKEUP;
		smp_wmb();
		/* make sure to read SQ tail after writing flags */
		smp_mb();

		if (!io_get_sqring(ctx, &sqes[0])) {
		if (kthread_should_stop()) {