Re: [PATCH V3 5/7] ublk_drv: consider recovery feature in aborting mechanism

On 2022/9/20 12:01, Ming Lei wrote:

On Tue, Sep 20, 2022 at 11:24:12AM +0800, Ziyang Zhang wrote:

quoted

On 2022/9/20 11:04, Ming Lei wrote:

quoted

On Tue, Sep 20, 2022 at 09:49:33AM +0800, Ziyang Zhang wrote:

Follows the delta patch against patch 5 for showing the idea:

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 4409a130d0b6..60c5786c4711 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c

@@ -656,7 +656,8 @@ static void ublk_complete_rq(struct request *req)
  * Also aborting may not be started yet, keep in mind that one failed
  * request may be issued by block layer again.
  */
-static void __ublk_fail_req(struct ublk_io *io, struct request *req)
+static void __ublk_fail_req(struct ublk_queue *ubq, struct ublk_io *io,
+		struct request *req)
 {
 	WARN_ON_ONCE(io->flags & UBLK_IO_FLAG_ACTIVE);
 

@@ -667,7 +668,10 @@ static void __ublk_fail_req(struct ublk_io *io, struct request *req)
 				req->tag,
 				io->flags);
 		io->flags |= UBLK_IO_FLAG_ABORTED;
-		blk_mq_end_request(req, BLK_STS_IOERR);
+		if (ublk_queue_can_use_recovery_reissue(ubq))
+			blk_mq_requeue_request(req, false);

Here is one problem:
We reset io->flags to 0 in ublk_queue_reinit() and it is called before new

As we agreed, ublk_queue_reinit() will be moved to ublk_ch_release(), when there isn't
any inflight request, which is completed by either ublk server or __ublk_fail_req().

So clearing io->flags isn't related with quisceing device.

quoted

ubq_daemon with FETCH_REQ is accepted. ublk_abort_queue() is not protected with
ub_mutex and it is called many times in monitor_work. So same rq may be requeued
multiple times.

UBLK_IO_FLAG_ABORTED is set for the slot, so one req is only ended or
requeued just once.

Yes, we can move ublk_queue_reinit() into ublk_ch_release(), but monitor_work is scheduled
periodically so ublk_abort_queue() is called multiple times. As ublk_queue_reinit() clear
io->flags, ublk_abort_queue() can requeue the same rq twice. Note that monitor_work can be
scheduled after ublk_ch_release().
 

quoted

With recovery disabled, there is no such problem since io->flags does not change
until ublk_dev is released.

But we have agreed that ublk_queue_reinit() can be moved to release
handler of /dev/ublkcN.

quoted

In my patch 5 I only requeue the same rq once. So re-using ublk_abort_queue() is
hard for recovery feature.

No, the same rq is just requeued once. Here the point is:

1) reuse previous pattern in ublk_stop_dev(), which is proved as
workable reliably

2) avoid to stay in half-working state forever

3) the behind idea is more simpler.

Ming, your patch requeue rqs with ACTVE unset. these rqs have been issued to the
dying ubq_daemon. What I concern about is inflight rqs with ACTIVE set.

Regards,
Zhang.