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io_uring: fix race condition reading SQ entries

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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 <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
This commit is contained in:
Stefan Bühler 2019-04-19 11:57:44 +02:00 • committed by Jens Axboe
commit e523a29c4f
1 changed files with 2 additions and 1 deletions
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3
fs/io_uring.c
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@ -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]);