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Subject[PATCH 5.2 201/215] io_uring: fix the sequence comparison in io_sequence_defer
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From: Zhengyuan Liu <liuzhengyuan@kylinos.cn>

commit dbd0f6d6c2a11eb9c31ca9cd454f95bb5713e92e upstream.

sq->cached_sq_head and cq->cached_cq_tail are both unsigned int. If
cached_sq_head overflows before cached_cq_tail, then we may miss a
barrier req. As cached_cq_tail always follows cached_sq_head, the NQ
should be enough.

Cc: stable@vger.kernel.org
Fixes: de0617e46717 ("io_uring: add support for marking commands as draining")
Signed-off-by: Zhengyuan Liu <liuzhengyuan@kylinos.cn>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/io_uring.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -425,7 +425,7 @@ static inline bool io_sequence_defer(str
if ((req->flags & (REQ_F_IO_DRAIN|REQ_F_IO_DRAINED)) != REQ_F_IO_DRAIN)
return false;

- return req->sequence > ctx->cached_cq_tail + ctx->sq_ring->dropped;
+ return req->sequence != ctx->cached_cq_tail + ctx->sq_ring->dropped;
}

static struct io_kiocb *io_get_deferred_req(struct io_ring_ctx *ctx)

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