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authorJens Axboe <axboe@kernel.dk>2019-04-17 16:57:48 +0200
committerJens Axboe <axboe@kernel.dk>2019-04-17 19:41:49 +0200
commit74f464e97044da33b25aaed00213914b0edf1f2e (patch)
tree47875b487bcdb6a18648c270b6b6b4f251ca5ce0 /fs
parentio_uring: fix possible deadlock between io_uring_{enter,register} (diff)
downloadlinux-74f464e97044da33b25aaed00213914b0edf1f2e.tar.xz
linux-74f464e97044da33b25aaed00213914b0edf1f2e.zip
io_uring: fix CQ overflow condition
This is a leftover from when the rings initially were not free flowing, and hence a test for tail + 1 == head would indicate full. Since we now let them wrap instead of mask them with the size, we need to check if they drift more than the ring size from each other. This fixes a case where we'd overwrite CQ ring entries, if the user failed to reap completions. Both cases would ultimately result in lost completions as the application violated the depth it asked for. The only difference is that before this fix we'd return invalid entries for the overflowed completions, instead of properly flagging it in the cq_ring->overflow variable. Reported-by: Stefan Bühler <source@stbuehler.de> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'fs')
-rw-r--r--fs/io_uring.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/io_uring.c b/fs/io_uring.c
index b35300e4c9a7..f65f85d89217 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -338,7 +338,7 @@ static struct io_uring_cqe *io_get_cqring(struct io_ring_ctx *ctx)
tail = ctx->cached_cq_tail;
/* See comment at the top of the file */
smp_rmb();
- if (tail + 1 == READ_ONCE(ring->r.head))
+ if (tail - READ_ONCE(ring->r.head) == ring->ring_entries)
return NULL;
ctx->cached_cq_tail++;