blk-mq: avoid double ->queue_rq() because of early timeout

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2139962
Upstream Status: merged to for-6.2/block

commit 82c229476b8f6afd7e09bc4dc77d89dc19ff7688
Author: David Jeffery <djeffery@redhat.com>
Date:   Wed Oct 26 13:19:57 2022 +0800

    blk-mq: avoid double ->queue_rq() because of early timeout

    David Jeffery found one double ->queue_rq() issue, so far it can
    be triggered in VM use case because of long vmexit latency or preempt
    latency of vCPU pthread or long page fault in vCPU pthread, then block
    IO req could be timed out before queuing the request to hardware but after
    calling blk_mq_start_request() during ->queue_rq(), then timeout handler
    may handle it by requeue, then double ->queue_rq() is caused, and kernel
    panic.

    So far, it is driver's responsibility to cover the race between timeout
    and completion, so it seems supposed to be solved in driver in theory,
    given driver has enough knowledge.

    But it is really one common problem, lots of driver could have similar
    issue, and could be hard to fix all affected drivers, even it isn't easy
    for driver to handle the race. So David suggests this patch by draining
    in-progress ->queue_rq() for solving this issue.

    Cc: Stefan Hajnoczi <stefanha@redhat.com>
    Cc: Keith Busch <kbusch@kernel.org>
    Cc: virtualization@lists.linux-foundation.org
    Cc: Bart Van Assche <bvanassche@acm.org>
    Signed-off-by: David Jeffery <djeffery@redhat.com>
    Signed-off-by: Ming Lei <ming.lei@redhat.com>
    Reviewed-by: Bart Van Assche <bvanassche@acm.org>
    Link: https://lore.kernel.org/r/20221026051957.358818-1-ming.lei@redhat.com
    Signed-off-by: Jens Axboe <axboe@kernel.dk>

Signed-off-by: Ming Lei <ming.lei@redhat.com>

block/blk-mq.c

@@ -1522,7 +1522,13 @@ static void blk_mq_rq_timed_out(struct request *req)
 	blk_add_timer(req);
 }
 
-static bool blk_mq_req_expired(struct request *rq, unsigned long *next)
+struct blk_expired_data {
+	bool has_timedout_rq;
+	unsigned long next;
+	unsigned long timeout_start;
+};
+
+static bool blk_mq_req_expired(struct request *rq, struct blk_expired_data *expired)
 {
 	unsigned long deadline;
 
@@ -1532,13 +1538,13 @@ static bool blk_mq_req_expired(struct request *rq, unsigned long *next)
 		return false;
 
 	deadline = READ_ONCE(rq->deadline);
-	if (time_after_eq(jiffies, deadline))
+	if (time_after_eq(expired->timeout_start, deadline))
 		return true;
 
-	if (*next == 0)
-		*next = deadline;
-	else if (time_after(*next, deadline))
-		*next = deadline;
+	if (expired->next == 0)
+		expired->next = deadline;
+	else if (time_after(expired->next, deadline))
+		expired->next = deadline;
 	return false;
 }
 
@@ -1554,7 +1560,7 @@ void blk_mq_put_rq_ref(struct request *rq)
 
 static bool blk_mq_check_expired(struct request *rq, void *priv)
 {
-	unsigned long *next = priv;
+	struct blk_expired_data *expired = priv;
 
 	/*
 	 * blk_mq_queue_tag_busy_iter() has locked the request, so it cannot
@@ -1563,7 +1569,18 @@ static bool blk_mq_check_expired(struct request *rq, void *priv)
 	 * it was completed and reallocated as a new request after returning
 	 * from blk_mq_check_expired().
 	 */
-	if (blk_mq_req_expired(rq, next))
+	if (blk_mq_req_expired(rq, expired)) {
+		expired->has_timedout_rq = true;
+		return false;
+	}
+	return true;
+}
+
+static bool blk_mq_handle_expired(struct request *rq, void *priv)
+{
+	struct blk_expired_data *expired = priv;
+
+	if (blk_mq_req_expired(rq, expired))
 		blk_mq_rq_timed_out(rq);
 	return true;
 }
@@ -1572,7 +1589,9 @@ static void blk_mq_timeout_work(struct work_struct *work)
 {
 	struct request_queue *q =
 		container_of(work, struct request_queue, timeout_work);
-	unsigned long next = 0;
+	struct blk_expired_data expired = {
+		.timeout_start = jiffies,
+	};
 	struct blk_mq_hw_ctx *hctx;
 	unsigned long i;
 
@@ -1592,10 +1611,23 @@ static void blk_mq_timeout_work(struct work_struct *work)
 	if (!percpu_ref_tryget(&q->q_usage_counter))
 		return;
 
-	blk_mq_queue_tag_busy_iter(q, blk_mq_check_expired, &next);
+	/* check if there is any timed-out request */
+	blk_mq_queue_tag_busy_iter(q, blk_mq_check_expired, &expired);
+	if (expired.has_timedout_rq) {
+		/*
+		 * Before walking tags, we must ensure any submit started
+		 * before the current time has finished. Since the submit
+		 * uses srcu or rcu, wait for a synchronization point to
+		 * ensure all running submits have finished
+		 */
+		blk_mq_wait_quiesce_done(q);
 
-	if (next != 0) {
-		mod_timer(&q->timeout, next);
+		expired.next = 0;
+		blk_mq_queue_tag_busy_iter(q, blk_mq_handle_expired, &expired);
+	}
+
+	if (expired.next != 0) {
+		mod_timer(&q->timeout, expired.next);
 	} else {
 		/*
 		 * Request timeouts are handled as a forward rolling timer. If