Patch "nvme: improve handling of long keep alives" has been added to the 6.3-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    nvme: improve handling of long keep alives

to the 6.3-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:
     nvme-improve-handling-of-long-keep-alives.patch
and it can be found in the queue-6.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit ddb9bf3451586e0fe95ea6302002dcc35e2007cb
Author: Uday Shankar <ushankar@xxxxxxxxxxxxxxx>
Date:   Thu May 25 12:22:04 2023 -0600

    nvme: improve handling of long keep alives
    
    [ Upstream commit c7275ce6a5fd32ca9f5a6294ed89cf0523181af9 ]
    
    Upon keep alive completion, nvme_keep_alive_work is scheduled with the
    same delay every time. If keep alive commands are completing slowly,
    this may cause a keep alive timeout. The following trace illustrates the
    issue, taking KATO = 8 and TBKAS off for simplicity:
    
    1. t = 0: run nvme_keep_alive_work, send keep alive
    2. t = ε: keep alive reaches controller, controller restarts its keep
              alive timer
    3. t = 4: host receives keep alive completion, schedules
              nvme_keep_alive_work with delay 4
    4. t = 8: run nvme_keep_alive_work, send keep alive
    
    Here, a keep alive having RTT of 4 causes a delay of at least 8 - ε
    between the controller receiving successive keep alives. With ε small,
    the controller is likely to detect a keep alive timeout.
    
    Fix this by calculating the RTT of the keep alive command, and adjusting
    the scheduling delay of the next keep alive work accordingly.
    
    Reported-by: Costa Sapuntzakis <costa@xxxxxxxxxxxxxxx>
    Reported-by: Randy Jennings <randyj@xxxxxxxxxxxxxxx>
    Signed-off-by: Uday Shankar <ushankar@xxxxxxxxxxxxxxx>
    Reviewed-by: Hannes Reinecke <hare@xxxxxxx>
    Reviewed-by: Christoph Hellwig <hch@xxxxxx>
    Signed-off-by: Keith Busch <kbusch@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index d87b8dfda622a..8a632bf7f5a8f 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -1199,6 +1199,20 @@ static enum rq_end_io_ret nvme_keep_alive_end_io(struct request *rq,
 	struct nvme_ctrl *ctrl = rq->end_io_data;
 	unsigned long flags;
 	bool startka = false;
+	unsigned long rtt = jiffies - (rq->deadline - rq->timeout);
+	unsigned long delay = nvme_keep_alive_work_period(ctrl);
+
+	/*
+	 * Subtract off the keepalive RTT so nvme_keep_alive_work runs
+	 * at the desired frequency.
+	 */
+	if (rtt <= delay) {
+		delay -= rtt;
+	} else {
+		dev_warn(ctrl->device, "long keepalive RTT (%u ms)\n",
+			 jiffies_to_msecs(rtt));
+		delay = 0;
+	}
 
 	blk_mq_free_request(rq);
 
@@ -1217,7 +1231,7 @@ static enum rq_end_io_ret nvme_keep_alive_end_io(struct request *rq,
 		startka = true;
 	spin_unlock_irqrestore(&ctrl->lock, flags);
 	if (startka)
-		nvme_queue_keep_alive_work(ctrl);
+		queue_delayed_work(nvme_wq, &ctrl->ka_work, delay);
 	return RQ_END_IO_NONE;
 }