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authorStefan Bühler <source@stbuehler.de>2019-04-19 11:57:44 +0200
committerJens Axboe <axboe@kernel.dk>2019-04-22 11:00:55 -0600
commite523a29c4f2703bdb98f68ce1bb256e259fd8d5f (patch)
tree0ba64403279546f48c7a7839c935ddbc110fa7df /fs/io_uring.c
parent35fa71a030caa50458a043560d4814ea9bcd639f (diff)
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>
Diffstat (limited to 'fs/io_uring.c')
-rw-r--r--fs/io_uring.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/fs/io_uring.c b/fs/io_uring.c
index a2f39faed6a7..41e3a6f6a096 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -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]);