[PATCH 7.2 61/88] io_uring/timeout: dont put a sequence target behind the last flush

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

7.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jens Axboe <axboe@kernel.dk>

Commit fdfce905a58edea053ee7b68b5bd4348dd1b36e0 upstream.

io_timeout_fn() and io_kill_timeout() bump ->cq_timeouts when a timeout
fires, but its CQE is only posted later from task_work. Until then the
sequence io_timeout() computes is one below the last flush per fired
timeout. Now that ->cq_last_tm_flush is kept while sequence timeouts are
pending, a timeout armed in that window with a small offset gets a target
behind the base. Its distance from the base wraps, and it's never
completed by events, only by its timer. With DEFER_TASKRUN that window
is as wide as the application makes it, as submission runs before the
local task_work.

Nothing but those in flight CQEs separates the two, so use the last
flush as the base for the target when the sequence is behind it.

Fixes: c6c0b3eba88c ("io_uring/timeout: don't skip over reached sequences")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 io_uring/timeout.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/io_uring/timeout.c
+++ b/io_uring/timeout.c
@@ -690,7 +690,6 @@ int io_timeout(struct io_kiocb *req, uns
 	}
 
 	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, it only
@@ -705,6 +704,15 @@ int io_timeout(struct io_kiocb *req, uns
 	base = ctx->cq_last_tm_flush;
 
 	/*
+	 * A fired timeout bumps ->cq_timeouts before its CQE is posted, which
+	 * leaves the sequence behind the last flush until it is. Nothing else
+	 * separates the two then, so count from the flush.
+	 */
+	if ((s32)(tail - base) < 0)
+		tail = base;
+	timeout->target_seq = tail + off;
+
+	/*
 	 * Insertion sort, ensuring the first entry in the list is always
 	 * the one we need first.
 	 */