FAILED: patch "[PATCH] block: mq-deadline: Fix dd_finish_request() for zoned devices" failed to apply to 5.15-stable tree

commit 2820e5d0820ac4daedff1272616a53d9c7682fd2 upstream.

dd_finish_request() tests if the per prio fifo_list is not empty to determine if request dispatching must be restarted for handling blocked write requests to zoned devices with a call to blk_mq_sched_mark_restart_hctx(). While simple, this implementation has 2 problems:

1) Only the priority level of the completed request is considered. However, writes to a zone may be blocked due to other writes to the same zone using a different priority level. While this is unlikely to happen in practice, as writing a zone with different IO priorirites does not make sense, nothing in the code prevents this from happening.
2) The use of list_empty() is dangerous as dd_finish_request() does not take dd->lock and may run concurrently with the insert and dispatch code.

Fix these 2 problems by testing the write fifo list of all priority levels using the new helper dd_has_write_work(), and by testing each fifo list using list_empty_careful().

Fixes c807ab520fc3 ("block/mq-deadline: Add I/O priority support")

Cc <[email protected]>

Signed-off-by Damien Le Moal <[email protected]>

Reviewed-by Johannes Thumshirn <[email protected]>

Link https://lore.kernel.org/r/[email protected] open here

Signed-off-by Jens Axboe <[email protected]>

---
 block/mq-deadline.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Possible dependencies:

2820e5d0820a ("block: mq-deadline: Fix dd_finish_request() for zoned devices")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2820e5d0820ac4daedff1272616a53d9c7682fd2 Mon Sep 17 00:00:00 2001
From: Damien Le Moal <[email protected]>
Date: Thu, 24 Nov 2022 11:12:07 +0900
Subject: [PATCH] block: mq-deadline: Fix dd_finish_request() for zoned devices

dd_finish_request() tests if the per prio fifo_list is not empty to determine if request dispatching must be restarted for handling blocked write requests to zoned devices with a call to blk_mq_sched_mark_restart_hctx(). While simple, this implementation has 2 problems:

1) Only the priority level of the completed request is considered. However, writes to a zone may be blocked due to other writes to the same zone using a different priority level. While this is unlikely to happen in practice, as writing a zone with different IO priorirites does not make sense, nothing in the code prevents this from happening.
2) The use of list_empty() is dangerous as dd_finish_request() does not take dd->lock and may run concurrently with the insert and dispatch code.

Fix these 2 problems by testing the write fifo list of all priority levels using the new helper dd_has_write_work(), and by testing each fifo list using list_empty_careful().

Fixes c807ab520fc3 ("block/mq-deadline: Add I/O priority support")

Cc <[email protected]>

Signed-off-by Damien Le Moal <[email protected]>

Reviewed-by Johannes Thumshirn <[email protected]>

Link https://lore.kernel.org/r/[email protected] open here

Signed-off-by Jens Axboe <[email protected]>

block/mq-deadline.c +15 -2

index 5639921dfa92..36374481cb87 100644
@@ -789,6 +789,18 @@ static void dd_prepare_request(struct request *rq)
 	rq->elv.priv[0] = NULL;
 }
 
+static bool dd_has_write_work(struct blk_mq_hw_ctx *hctx)
+{
+	struct deadline_data *dd = hctx->queue->elevator->elevator_data;
+	enum dd_prio p;
+
+	for (p = 0; p <= DD_PRIO_MAX; p++)
+		if (!list_empty_careful(&dd->per_prio[p].fifo_list[DD_WRITE]))
+			return true;
+
+	return false;
+}
+
 /*
  * Callback from inside blk_mq_free_request().
  *

@@ -828,9 +840,10 @@ static void dd_finish_request(struct request *rq)
 
 		spin_lock_irqsave(&dd->zone_lock, flags);
 		blk_req_zone_write_unlock(rq);
-		if (!list_empty(&per_prio->fifo_list[DD_WRITE]))
-			blk_mq_sched_mark_restart_hctx(rq->mq_hctx);
 		spin_unlock_irqrestore(&dd->zone_lock, flags);
+
+		if (dd_has_write_work(rq->mq_hctx))
+			blk_mq_sched_mark_restart_hctx(rq->mq_hctx);
 	}
 }