io_uring: annotate offset timeout races

commit 5498bf2 upstream.

It's racy to read ->cached_cq_tail without taking proper measures
(usually grabbing ->completion_lock) as timeout requests with CQE
offsets do, however they have never had a good semantics for from
when they start counting. Annotate racy reads with data_race().

Reported-by: [email protected]
Signed-off-by: Pavel Begunkov <[email protected]>
Link: https://lore.kernel.org/r/4de3685e185832a92a572df2be2c735d2e21a83d.1684506056.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: isilence

io_uring/timeout.c

@@ -545,7 +545,7 @@ int io_timeout(struct io_kiocb *req, unsigned int issue_flags)
 		goto add;
 	}
 
-	tail = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts);
+	tail = data_race(ctx->cached_cq_tail) - atomic_read(&ctx->cq_timeouts);
 	timeout->target_seq = tail + off;
 
 	/* Update the last seq here in case io_flush_timeouts() hasn't.