Commit e523a29c authored Apr 19, 2019 by Stefan Bühler Committed by Jens Axboe Apr 22, 2019

io_uring: fix race condition reading SQ entries



A read memory barrier is required between reading SQ tail and reading
the actual data belonging to the SQ entry.

Userspace needs a matching write barrier between writing SQ entries and
updating SQ tail (using smp_store_release to update tail will do).

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

parent 35fa71a0

fs/io_uring.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -1739,7 +1739,8 @@ static bool io_get_sqring(struct io_ring_ctx ctx, struct sqe_submit s)
		head = ctx->cached_sq_head;
		/* See comment at the top of this file */
		smp_rmb();
		if (head == READ_ONCE(ring->r.tail))
		/* make sure SQ entry isn't read before tail */
		if (head == smp_load_acquire(&ring->r.tail))
		return false;

		head = READ_ONCE(ring->array[head & ctx->sq_mask]);