This is a note to let you know that I've just added the patch titled
blk-mq: avoid double ->queue_rq() because of early timeout
to the 6.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
blk-mq-avoid-double-queue_rq-because-of-early-timeou.patch
and it can be found in the queue-6.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit dbe0e68e1a1a2d634dd3b7a4564f2a7098079960
Author: David Jeffery <djeffery@xxxxxxxxxx>
Date: Wed Oct 26 13:19:57 2022 +0800
blk-mq: avoid double ->queue_rq() because of early timeout
[ Upstream commit 82c229476b8f6afd7e09bc4dc77d89dc19ff7688 ]
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@xxxxxxxxxx>
Cc: Keith Busch <kbusch@xxxxxxxxxx>
Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: Bart Van Assche <bvanassche@xxxxxxx>
Signed-off-by: David Jeffery <djeffery@xxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
Reviewed-by: Bart Van Assche <bvanassche@xxxxxxx>
Link: https://lore.kernel.org/r/20221026051957.358818-1-ming.lei@xxxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 88975170cc32..05e33c51702d 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1442,7 +1442,13 @@ 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;
@@ -1452,13 +1458,13 @@ 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;
}
@@ -1472,7 +1478,7 @@ 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
@@ -1481,7 +1487,18 @@ 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;
}
@@ -1490,7 +1507,9 @@ 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;
@@ -1510,10 +1529,23 @@ 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);
+
+ expired.next = 0;
+ blk_mq_queue_tag_busy_iter(q, blk_mq_handle_expired, &expired);
+ }
- if (next != 0) {
- mod_timer(&q->timeout, next);
+ if (expired.next != 0) {
+ mod_timer(&q->timeout, expired.next);
} else {
/*
* Request timeouts are handled as a forward rolling timer. If
