[RESEND PATCH v2 0/3] queue freezing improvement and cleanups

[RESEND PATCH v2 0/3] queue freezing improvement and cleanups

[Jinlong Chen]

Hi!

This series of patches improves and cleans up queue freezing in blk-mq.c
to build a clearer blk_mq_* namespace.

Changes in v2:
- improved descriptions in patch series title and patch 1 (suggested by
  Bart Van Assche <bvanassche@acm.org>).

Jinlong Chen (3):
  blk-mq: remove redundant call to blk_freeze_queue_start in
    blk_mq_destroy_queue
  blk-mq: remove blk_freeze_queue
  block: hide back blk_freeze_queue_start and export its blk-mq alias

 block/blk-core.c              | 13 +++++++++
 block/blk-mq.c                | 52 ++++++++++++++---------------------
 block/blk-pm.c                |  2 +-
 block/blk.h                   |  2 +-
 drivers/nvme/host/core.c      |  2 +-
 drivers/nvme/host/multipath.c |  2 +-
 include/linux/blk-mq.h        |  2 +-
 7 files changed, 39 insertions(+), 36 deletions(-)

-- 
2.31.1

[RESEND PATCH v2 1/3] blk-mq: remove redundant call to blk_freeze_queue_start in blk_mq_destroy_queue

[Jinlong Chen]

The calling relationship in blk_mq_destroy_queue() is as follows:

blk_mq_destroy_queue()
    ...
    -> blk_queue_start_drain()
        -> blk_freeze_queue_start()  <- called
        ...
    -> blk_freeze_queue()
        -> blk_freeze_queue_start()  <- called again
        -> blk_mq_freeze_queue_wait()

So there is a redundant call to blk_freeze_queue_start(). Replace
blk_freeze_queue() with blk_mq_freeze_queue_wait() to avoid the redundant
call.

Signed-off-by: Jinlong Chen <nickyc975@zju.edu.cn>
---
 block/blk-mq.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 4cecf281123f..14c4165511b9 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4005,7 +4005,12 @@ void blk_mq_destroy_queue(struct request_queue *q)
 
 	blk_queue_flag_set(QUEUE_FLAG_DYING, q);
 	blk_queue_start_drain(q);
-	blk_freeze_queue(q);
+
+	/*
+	 * blk_freeze_queue_start has been called in blk_queue_start_drain, we just
+	 * need to wait.
+	 */
+	blk_mq_freeze_queue_wait(q);
 
 	blk_sync_queue(q);
 	blk_mq_cancel_work_sync(q);
-- 
2.31.1

[RESEND PATCH v2 2/3] blk-mq: remove blk_freeze_queue

[Jinlong Chen]

Nobody is calling blk_freeze_queue except its alias, so remove it.

Signed-off-by: Jinlong Chen <nickyc975@zju.edu.cn>
---
 block/blk-mq.c | 18 +-----------------
 block/blk.h    |  1 -
 2 files changed, 1 insertion(+), 18 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 14c4165511b9..e0654a2e80b9 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -194,27 +194,11 @@ EXPORT_SYMBOL_GPL(blk_mq_freeze_queue_wait_timeout);
  * Guarantee no request is in use, so we can change any data structure of
  * the queue afterward.
  */
-void blk_freeze_queue(struct request_queue *q)
+void blk_mq_freeze_queue(struct request_queue *q)
 {
-	/*
-	 * In the !blk_mq case we are only calling this to kill the
-	 * q_usage_counter, otherwise this increases the freeze depth
-	 * and waits for it to return to zero.  For this reason there is
-	 * no blk_unfreeze_queue(), and blk_freeze_queue() is not
-	 * exported to drivers as the only user for unfreeze is blk_mq.
-	 */
 	blk_freeze_queue_start(q);
 	blk_mq_freeze_queue_wait(q);
 }
-
-void blk_mq_freeze_queue(struct request_queue *q)
-{
-	/*
-	 * ...just an alias to keep freeze and unfreeze actions balanced
-	 * in the blk_mq_* namespace
-	 */
-	blk_freeze_queue(q);
-}
 EXPORT_SYMBOL_GPL(blk_mq_freeze_queue);
 
 void __blk_mq_unfreeze_queue(struct request_queue *q, bool force_atomic)
diff --git a/block/blk.h b/block/blk.h
index 7f9e089ab1f7..e9addea2838a 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -37,7 +37,6 @@ struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,
 					      gfp_t flags);
 void blk_free_flush_queue(struct blk_flush_queue *q);
 
-void blk_freeze_queue(struct request_queue *q);
 void __blk_mq_unfreeze_queue(struct request_queue *q, bool force_atomic);
 void blk_queue_start_drain(struct request_queue *q);
 int __bio_queue_enter(struct request_queue *q, struct bio *bio);
-- 
2.31.1

[RESEND PATCH v2 3/3] block: hide back blk_freeze_queue_start and export its blk-mq alias

[Jinlong Chen]

blk_freeze_queue_start is used internally for universal queue draining and
externally for blk-mq specific queue freezing. Keep the non-blk-mq name
private and export a blk-mq alias to users.

Signed-off-by: Jinlong Chen <nickyc975@zju.edu.cn>
---
 block/blk-core.c              | 13 +++++++++++++
 block/blk-mq.c                | 27 ++++++++++++++-------------
 block/blk-pm.c                |  2 +-
 block/blk.h                   |  1 +
 drivers/nvme/host/core.c      |  2 +-
 drivers/nvme/host/multipath.c |  2 +-
 include/linux/blk-mq.h        |  2 +-
 7 files changed, 32 insertions(+), 17 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 5d50dd16e2a5..d3dd439a8ed4 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -269,6 +269,19 @@ void blk_put_queue(struct request_queue *q)
 }
 EXPORT_SYMBOL(blk_put_queue);
 
+void blk_freeze_queue_start(struct request_queue *q)
+{
+	mutex_lock(&q->mq_freeze_lock);
+	if (++q->mq_freeze_depth == 1) {
+		percpu_ref_kill(&q->q_usage_counter);
+		mutex_unlock(&q->mq_freeze_lock);
+		if (queue_is_mq(q))
+			blk_mq_run_hw_queues(q, false);
+	} else {
+		mutex_unlock(&q->mq_freeze_lock);
+	}
+}
+
 void blk_queue_start_drain(struct request_queue *q)
 {
 	/*
diff --git a/block/blk-mq.c b/block/blk-mq.c
index e0654a2e80b9..d638bd0fb4d8 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -161,19 +161,20 @@ void blk_mq_in_flight_rw(struct request_queue *q, struct block_device *part,
 	inflight[1] = mi.inflight[1];
 }
 
-void blk_freeze_queue_start(struct request_queue *q)
+void blk_mq_freeze_queue_start(struct request_queue *q)
 {
-	mutex_lock(&q->mq_freeze_lock);
-	if (++q->mq_freeze_depth == 1) {
-		percpu_ref_kill(&q->q_usage_counter);
-		mutex_unlock(&q->mq_freeze_lock);
-		if (queue_is_mq(q))
-			blk_mq_run_hw_queues(q, false);
-	} else {
-		mutex_unlock(&q->mq_freeze_lock);
-	}
+	/*
+	 * Warn on non-blk-mq usages.
+	 */
+	WARN_ON_ONCE(!queue_is_mq(q));
+
+	/*
+	 * Just an alias of blk_freeze_queue_start to keep the consistency of the
+	 * blk_mq_* namespace.
+	 */
+	blk_freeze_queue_start(q);
 }
-EXPORT_SYMBOL_GPL(blk_freeze_queue_start);
+EXPORT_SYMBOL_GPL(blk_mq_freeze_queue_start);
 
 void blk_mq_freeze_queue_wait(struct request_queue *q)
 {
@@ -196,7 +197,7 @@ EXPORT_SYMBOL_GPL(blk_mq_freeze_queue_wait_timeout);
  */
 void blk_mq_freeze_queue(struct request_queue *q)
 {
-	blk_freeze_queue_start(q);
+	blk_mq_freeze_queue_start(q);
 	blk_mq_freeze_queue_wait(q);
 }
 EXPORT_SYMBOL_GPL(blk_mq_freeze_queue);
@@ -1570,7 +1571,7 @@ static void blk_mq_timeout_work(struct work_struct *work)
 	 * percpu_ref_tryget directly, because we need to be able to
 	 * obtain a reference even in the short window between the queue
 	 * starting to freeze, by dropping the first reference in
-	 * blk_freeze_queue_start, and the moment the last request is
+	 * blk_mq_freeze_queue_start, and the moment the last request is
 	 * consumed, marked by the instant q_usage_counter reaches
 	 * zero.
 	 */
diff --git a/block/blk-pm.c b/block/blk-pm.c
index 2dad62cc1572..ae2b950ed45d 100644
--- a/block/blk-pm.c
+++ b/block/blk-pm.c
@@ -80,7 +80,7 @@ int blk_pre_runtime_suspend(struct request_queue *q)
 	blk_set_pm_only(q);
 	ret = -EBUSY;
 	/* Switch q_usage_counter from per-cpu to atomic mode. */
-	blk_freeze_queue_start(q);
+	blk_mq_freeze_queue_start(q);
 	/*
 	 * Wait until atomic mode has been reached. Since that
 	 * involves calling call_rcu(), it is guaranteed that later
diff --git a/block/blk.h b/block/blk.h
index e9addea2838a..ee576bb74382 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -37,6 +37,7 @@ struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,
 					      gfp_t flags);
 void blk_free_flush_queue(struct blk_flush_queue *q);
 
+void blk_freeze_queue_start(struct request_queue *q);
 void __blk_mq_unfreeze_queue(struct request_queue *q, bool force_atomic);
 void blk_queue_start_drain(struct request_queue *q);
 int __bio_queue_enter(struct request_queue *q, struct bio *bio);
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 0090dc0b3ae6..e2d5c54c651a 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -5199,7 +5199,7 @@ void nvme_start_freeze(struct nvme_ctrl *ctrl)
 
 	down_read(&ctrl->namespaces_rwsem);
 	list_for_each_entry(ns, &ctrl->namespaces, list)
-		blk_freeze_queue_start(ns->queue);
+		blk_mq_freeze_queue_start(ns->queue);
 	up_read(&ctrl->namespaces_rwsem);
 }
 EXPORT_SYMBOL_GPL(nvme_start_freeze);
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 0ea7e441e080..3bb358bd0cde 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -77,7 +77,7 @@ void nvme_mpath_start_freeze(struct nvme_subsystem *subsys)
 	lockdep_assert_held(&subsys->lock);
 	list_for_each_entry(h, &subsys->nsheads, entry)
 		if (h->disk)
-			blk_freeze_queue_start(h->disk->queue);
+			blk_mq_freeze_queue_start(h->disk->queue);
 }
 
 void nvme_failover_req(struct request *req)
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 569053ed959d..8600d4b4aa80 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -887,7 +887,7 @@ void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
 void blk_mq_tagset_wait_completed_request(struct blk_mq_tag_set *tagset);
 void blk_mq_freeze_queue(struct request_queue *q);
 void blk_mq_unfreeze_queue(struct request_queue *q);
-void blk_freeze_queue_start(struct request_queue *q);
+void blk_mq_freeze_queue_start(struct request_queue *q);
 void blk_mq_freeze_queue_wait(struct request_queue *q);
 int blk_mq_freeze_queue_wait_timeout(struct request_queue *q,
 				     unsigned long timeout);
-- 
2.31.1

Re: [RESEND PATCH v2 1/3] blk-mq: remove redundant call to blk_freeze_queue_start in blk_mq_destroy_queue

[Christoph Hellwig]

> -	blk_freeze_queue(q);
> +
> +	/*
> +	 * blk_freeze_queue_start has been called in blk_queue_start_drain, we just
> +	 * need to wait.
> +	 */


This commit is not only pointless, but also exceeds the 80 character
limit.

Re: [RESEND PATCH v2 2/3] blk-mq: remove blk_freeze_queue

[Christoph Hellwig]

On Sun, Oct 30, 2022 at 01:26:45PM +0800, Jinlong Chen wrote:
> Nobody is calling blk_freeze_queue except its alias, so remove it.

So while we really do not need both names - the queue freezing is also
used for non-mq drivers, so the naming without the mq is actually the
slightly more correct one.  But for that it should also move out of
blk-mq.c, so I'm not really sure touching this right now is all that
helpful.

Re: [RESEND PATCH v2 3/3] block: hide back blk_freeze_queue_start and export its blk-mq alias

[Christoph Hellwig]

On Sun, Oct 30, 2022 at 01:26:46PM +0800, Jinlong Chen wrote:
> blk_freeze_queue_start is used internally for universal queue draining and
> externally for blk-mq specific queue freezing. Keep the non-blk-mq name
> private and export a blk-mq alias to users.

I really don't see the point here.  Eventually all of the freezing
should move out of the mq namespace.  But that given that we have
actual technical work pending here I'd suggest to just leave it alone
for now, and just respin a version of patch 1 without the pointless
comment.

Re: [RESEND PATCH v2 3/3] block: hide back blk_freeze_queue_start and export its blk-mq alias

[Jinlong Chen]

> On Sun, Oct 30, 2022 at 01:26:46PM +0800, Jinlong Chen wrote:
> > blk_freeze_queue_start is used internally for universal queue draining and
> > externally for blk-mq specific queue freezing. Keep the non-blk-mq name
> > private and export a blk-mq alias to users.
> 
> I really don't see the point here.  Eventually all of the freezing
> should move out of the mq namespace.  But that given that we have
> actual technical work pending here I'd suggest to just leave it alone
> for now, and just respin a version of patch 1 without the pointless
> comment.

I agree that the freezing stuff (maybe also the quiescing stuff) should
move out of the mq namespace. If now is not the proper time, I'll leave
them alone. I'll resend patch 1 alone without the comment.

Thanks!
Jinlong Chen

Re: [RESEND PATCH v2 3/3] block: hide back blk_freeze_queue_start and export its blk-mq alias

[Christoph Hellwig]

On Sun, Oct 30, 2022 at 04:19:49PM +0800, Jinlong Chen wrote:
> I agree that the freezing stuff (maybe also the quiescing stuff) should
> move out of the mq namespace. If now is not the proper time, I'll leave
> them alone. I'll resend patch 1 alone without the comment.

The quiesce actually is entirely blk-mq specific, which just have some
careless callers.

Re: Re: [RESEND PATCH v2 3/3] block: hide back blk_freeze_queue_start and export its blk-mq alias

[Jinlong Chen]

> > I agree that the freezing stuff (maybe also the quiescing stuff) should
> > move out of the mq namespace. If now is not the proper time, I'll leave
> > them alone. I'll resend patch 1 alone without the comment.
> 
> The quiesce actually is entirely blk-mq specific, which just have some
> careless callers.

Got it, thank you!

Thanks!
Jinlong Chen