[PATCH 0/6] blk-mq: update_nr_hw_queues related improvement & bugfix

[PATCH 0/6] blk-mq: update_nr_hw_queues related improvement & bugfix

[Ming Lei]

Hi,

The 1st patch figures out correct numa node for each kind of hw queue.

The 2nd patch simplifies reallocation of q->queue_hw_ctx a bit.

The 3rd patch re-configures poll capability after queue map is changed.

The 4th patch changes mtip32xx to avoid to refer to q->queue_hw_ctx
directly.

The 5th & 6th patches fix use-after-free on q->queue_hw_ctx.


Ming Lei (6):
  blk-mq: figure out correct numa node for hw queue
  blk-mq: simplify reallocation of hw ctxs a bit
  blk-mq: re-config poll after queue map is changed
  block: mtip32xx: don't touch q->queue_hw_ctx
  blk-mq: add helper of blk_mq_get_hctx to retrieve hctx via its index
  blk-mq: manage hctx map via xarray

 block/blk-mq-sysfs.c              |   2 +-
 block/blk-mq-tag.c                |   2 +-
 block/blk-mq.c                    | 125 +++++++++++++++++-------------
 block/blk-mq.h                    |   2 +-
 drivers/block/mtip32xx/mtip32xx.c |   4 +-
 include/linux/blk-mq.h            |   8 +-
 include/linux/blkdev.h            |   2 +-
 7 files changed, 84 insertions(+), 61 deletions(-)

-- 
2.31.1

[PATCH 1/6] blk-mq: figure out correct numa node for hw queue

[Ming Lei]

The current code always uses default queue map and hw queue index
for figuring out the numa node for hw queue, this way isn't correct
because blk-mq supports three queue maps, and the correct queue map
should be used for the specified hw queue.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq.c | 36 ++++++++++++++++++++++++++++++------
 1 file changed, 30 insertions(+), 6 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index a05ce7725031..931add81813b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3107,15 +3107,41 @@ void blk_mq_free_rq_map(struct blk_mq_tags *tags)
 	blk_mq_free_tags(tags);
 }
 
+static int hctx_idx_to_type(struct blk_mq_tag_set *set,
+		unsigned int hctx_idx)
+{
+	int j;
+
+	for (j = 0; j < set->nr_maps; j++) {
+		unsigned int start =  set->map[j].queue_offset;
+		unsigned int end = start + set->map[j].nr_queues;
+
+		if (hctx_idx >= start && hctx_idx < end)
+			break;
+	}
+
+	if (j >= set->nr_maps)
+		j = HCTX_TYPE_DEFAULT;
+
+	return j;
+}
+
+static int blk_mq_get_hctx_node(struct blk_mq_tag_set *set,
+		unsigned int hctx_idx)
+{
+	int type = hctx_idx_to_type(set, hctx_idx);
+
+	return blk_mq_hw_queue_to_node(&set->map[type], hctx_idx);
+}
+
 static struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
 					       unsigned int hctx_idx,
 					       unsigned int nr_tags,
 					       unsigned int reserved_tags)
 {
 	struct blk_mq_tags *tags;
-	int node;
+	int node = blk_mq_get_hctx_node(set, hctx_idx);
 
-	node = blk_mq_hw_queue_to_node(&set->map[HCTX_TYPE_DEFAULT], hctx_idx);
 	if (node == NUMA_NO_NODE)
 		node = set->numa_node;
 
@@ -3165,9 +3191,8 @@ static int blk_mq_alloc_rqs(struct blk_mq_tag_set *set,
 {
 	unsigned int i, j, entries_per_page, max_order = 4;
 	size_t rq_size, left;
-	int node;
+	int node = blk_mq_get_hctx_node(set, hctx_idx);
 
-	node = blk_mq_hw_queue_to_node(&set->map[HCTX_TYPE_DEFAULT], hctx_idx);
 	if (node == NUMA_NO_NODE)
 		node = set->numa_node;
 
@@ -3941,10 +3966,9 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
 	/* protect against switching io scheduler  */
 	mutex_lock(&q->sysfs_lock);
 	for (i = 0; i < set->nr_hw_queues; i++) {
-		int node;
+		int node = blk_mq_get_hctx_node(set, i);
 		struct blk_mq_hw_ctx *hctx;
 
-		node = blk_mq_hw_queue_to_node(&set->map[HCTX_TYPE_DEFAULT], i);
 		/*
 		 * If the hw queue has been mapped to another numa node,
 		 * we need to realloc the hctx. If allocation fails, fallback
-- 
2.31.1

Re: [PATCH 1/6] blk-mq: figure out correct numa node for hw queue

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 1/6] blk-mq: figure out correct numa node for hw queue

[John Garry]

On 28/02/2022 09:04, Ming Lei wrote:
> The current code always uses default queue map and hw queue index
> for figuring out the numa node for hw queue, this way isn't correct
> because blk-mq supports three queue maps, and the correct queue map
> should be used for the specified hw queue.
> 
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---

Hi Ming,

Just some small comments to consider if you need to respin.

Thanks,
John

>   block/blk-mq.c | 36 ++++++++++++++++++++++++++++++------
>   1 file changed, 30 insertions(+), 6 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index a05ce7725031..931add81813b 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -3107,15 +3107,41 @@ void blk_mq_free_rq_map(struct blk_mq_tags *tags)
>   	blk_mq_free_tags(tags);
>   }
>   
> +static int 

enum hctx_type?

> hctx_idx_to_type(struct blk_mq_tag_set *set,
> +		unsigned int hctx_idx)
> +{
> +	int j;

super nit: normally use i

> +
> +	for (j = 0; j < set->nr_maps; j++) {
> +		unsigned int start =  set->map[j].queue_offset;

nit: double whitespace intentional?

> +		unsigned int end = start + set->map[j].nr_queues;
> +
> +		if (hctx_idx >= start && hctx_idx < end)
> +			break;
> +	}
> +
> +	if (j >= set->nr_maps)
> +		j = HCTX_TYPE_DEFAULT;
> +
> +	return j;
> +}
> +
> +static int blk_mq_get_hctx_node(struct blk_mq_tag_set *set,
> +		unsigned int hctx_idx)
> +{
> +	int type = hctx_idx_to_type(set, hctx_idx);
> +
> +	return blk_mq_hw_queue_to_node(&set->map[type], hctx_idx);
> +}
> +
>   static struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
>   					       unsigned int hctx_idx,
>   					       unsigned int nr_tags,
>   					       unsigned int reserved_tags)
>   {
>   	struct blk_mq_tags *tags;
> -	int node;
> +	int node = blk_mq_get_hctx_node(set, hctx_idx);

nit: the code originally had reverse firtree ordering, which I suppose 
is not by mistake

>   
> -	node = blk_mq_hw_queue_to_node(&set->map[HCTX_TYPE_DEFAULT], hctx_idx);
>   	if (node == NUMA_NO_NODE)
>   		node = set->numa_node;
>   
> @@ -3165,9 +3191,8 @@ static int blk_mq_alloc_rqs(struct blk_mq_tag_set *set,
>   {
>   	unsigned int i, j, entries_per_page, max_order = 4;
>   	size_t rq_size, left;
> -	int node;
> +	int node = blk_mq_get_hctx_node(set, hctx_idx);

and here

>   
> -	node = blk_mq_hw_queue_to_node(&set->map[HCTX_TYPE_DEFAULT], hctx_idx);
>   	if (node == NUMA_NO_NODE)
>   		node = set->numa_node;
>   
> @@ -3941,10 +3966,9 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
>   	/* protect against switching io scheduler  */
>   	mutex_lock(&q->sysfs_lock);
>   	for (i = 0; i < set->nr_hw_queues; i++) {
> -		int node;
> +		int node = blk_mq_get_hctx_node(set, i);
>   		struct blk_mq_hw_ctx *hctx;
>   
> -		node = blk_mq_hw_queue_to_node(&set->map[HCTX_TYPE_DEFAULT], i);
>   		/*
>   		 * If the hw queue has been mapped to another numa node,
>   		 * we need to realloc the hctx. If allocation fails, fallback

Re: [PATCH 1/6] blk-mq: figure out correct numa node for hw queue

[Ming Lei]

On Tue, Mar 01, 2022 at 07:19:43PM +0000, John Garry wrote:
> On 28/02/2022 09:04, Ming Lei wrote:
> > The current code always uses default queue map and hw queue index
> > for figuring out the numa node for hw queue, this way isn't correct
> > because blk-mq supports three queue maps, and the correct queue map
> > should be used for the specified hw queue.
> > 
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > ---
> 
> Hi Ming,
> 
> Just some small comments to consider if you need to respin.
> 
> Thanks,
> John
> 
> >   block/blk-mq.c | 36 ++++++++++++++++++++++++++++++------
> >   1 file changed, 30 insertions(+), 6 deletions(-)
> > 
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index a05ce7725031..931add81813b 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -3107,15 +3107,41 @@ void blk_mq_free_rq_map(struct blk_mq_tags *tags)
> >   	blk_mq_free_tags(tags);
> >   }
> >    +static int
> 
> enum hctx_type?
> 
> > hctx_idx_to_type(struct blk_mq_tag_set *set,
> > +		unsigned int hctx_idx)
> > +{
> > +	int j;
> 
> super nit: normally use i

OK

> 
> > +
> > +	for (j = 0; j < set->nr_maps; j++) {
> > +		unsigned int start =  set->map[j].queue_offset;
> 
> nit: double whitespace intentional?

will fix it.

> 
> > +		unsigned int end = start + set->map[j].nr_queues;
> > +
> > +		if (hctx_idx >= start && hctx_idx < end)
> > +			break;
> > +	}
> > +
> > +	if (j >= set->nr_maps)
> > +		j = HCTX_TYPE_DEFAULT;
> > +
> > +	return j;
> > +}
> > +
> > +static int blk_mq_get_hctx_node(struct blk_mq_tag_set *set,
> > +		unsigned int hctx_idx)
> > +{
> > +	int type = hctx_idx_to_type(set, hctx_idx);
> > +
> > +	return blk_mq_hw_queue_to_node(&set->map[type], hctx_idx);
> > +}
> > +
> >   static struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
> >   					       unsigned int hctx_idx,
> >   					       unsigned int nr_tags,
> >   					       unsigned int reserved_tags)
> >   {
> >   	struct blk_mq_tags *tags;
> > -	int node;
> > +	int node = blk_mq_get_hctx_node(set, hctx_idx);
> 
> nit: the code originally had reverse firtree ordering, which I suppose is
> not by mistake

What is reverse firtree ordering here? I don't know what is wrong
with the above one line change from patch style viewpoint, and
checkpatch complains nothing here.


Thanks,
Ming

Re: [PATCH 1/6] blk-mq: figure out correct numa node for hw queue

[John Garry]

On 02/03/2022 01:47, Ming Lei wrote:
>>>    static struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
>>>    					       unsigned int hctx_idx,
>>>    					       unsigned int nr_tags,
>>>    					       unsigned int reserved_tags)
>>>    {
>>>    	struct blk_mq_tags *tags;
>>> -	int node;
>>> +	int node = blk_mq_get_hctx_node(set, hctx_idx);
>> nit: the code originally had reverse firtree ordering, which I suppose is
>> not by mistake
> What is reverse firtree ordering here? I don't know what is wrong
> with the above one line change from patch style viewpoint, and
> checkpatch complains nothing here.

checkpath would not complain about this. I'm talking about:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/maintainer-tip.rst#n587

The original code had:

	struct blk_mq_tags *tags;
	int node;

as opposed to:

	int node;
	struct blk_mq_tags *tags;

That's all. The block code seems to mostly follow this style when 
possible. It's just a style issue.

thanks,
John

Re: [PATCH 1/6] blk-mq: figure out correct numa node for hw queue

[Ming Lei]

On Wed, Mar 02, 2022 at 09:02:53AM +0000, John Garry wrote:
> On 02/03/2022 01:47, Ming Lei wrote:
> > > >    static struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
> > > >    					       unsigned int hctx_idx,
> > > >    					       unsigned int nr_tags,
> > > >    					       unsigned int reserved_tags)
> > > >    {
> > > >    	struct blk_mq_tags *tags;
> > > > -	int node;
> > > > +	int node = blk_mq_get_hctx_node(set, hctx_idx);
> > > nit: the code originally had reverse firtree ordering, which I suppose is
> > > not by mistake
> > What is reverse firtree ordering here? I don't know what is wrong
> > with the above one line change from patch style viewpoint, and
> > checkpatch complains nothing here.
> 
> checkpath would not complain about this. I'm talking about:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/maintainer-tip.rst#n587
> 
> The original code had:
> 
> 	struct blk_mq_tags *tags;
> 	int node;
> 
> as opposed to:
> 
> 	int node;
> 	struct blk_mq_tags *tags;
> 
> That's all. The block code seems to mostly follow this style when possible.
> It's just a style issue.

But my patch doesn't change the order, :-)


Thanks,
Ming

Re: [PATCH 1/6] blk-mq: figure out correct numa node for hw queue

[John Garry]

On 02/03/2022 09:22, Ming Lei wrote:
>>> What is reverse firtree ordering here? I don't know what is wrong
>>> with the above one line change from patch style viewpoint, and
>>> checkpatch complains nothing here.
>> checkpath would not complain about this. I'm talking about:
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/maintainer-tip.rst#n587
>>
>> The original code had:
>>
>> 	struct blk_mq_tags *tags;
>> 	int node;
>>
>> as opposed to:
>>
>> 	int node;
>> 	struct blk_mq_tags *tags;
>>
>> That's all. The block code seems to mostly follow this style when possible.
>> It's just a style issue.
> But my patch doesn't change the order,:-)

Right, and I am just saying that if you were to maintain this coding 
style then it should. But, as I alluded before, for only 2 declarations 
is not so important.

Thanks,
John

[PATCH 2/6] blk-mq: simplify reallocation of hw ctxs a bit

[Ming Lei]

blk_mq_alloc_and_init_hctx() has already taken reuse into account, so
no need to do it outside, then we can simplify blk_mq_realloc_hw_ctxs().

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq.c | 33 ++++++++++++++-------------------
 1 file changed, 14 insertions(+), 19 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 931add81813b..361903f07c84 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3966,29 +3966,24 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
 	/* protect against switching io scheduler  */
 	mutex_lock(&q->sysfs_lock);
 	for (i = 0; i < set->nr_hw_queues; i++) {
+		int old_node;
 		int node = blk_mq_get_hctx_node(set, i);
-		struct blk_mq_hw_ctx *hctx;
+		struct blk_mq_hw_ctx *old_hctx = hctxs[i];
 
-		/*
-		 * If the hw queue has been mapped to another numa node,
-		 * we need to realloc the hctx. If allocation fails, fallback
-		 * to use the previous one.
-		 */
-		if (hctxs[i] && (hctxs[i]->numa_node == node))
-			continue;
+		if (old_hctx) {
+			old_node = old_hctx->numa_node;
+			blk_mq_exit_hctx(q, set, old_hctx, i);
+		}
 
-		hctx = blk_mq_alloc_and_init_hctx(set, q, i, node);
-		if (hctx) {
-			if (hctxs[i])
-				blk_mq_exit_hctx(q, set, hctxs[i], i);
-			hctxs[i] = hctx;
-		} else {
-			if (hctxs[i])
-				pr_warn("Allocate new hctx on node %d fails,\
-						fallback to previous one on node %d\n",
-						node, hctxs[i]->numa_node);
-			else
+		hctxs[i] = blk_mq_alloc_and_init_hctx(set, q, i, node);
+		if (!hctxs[i]) {
+			if (!old_hctx)
 				break;
+			pr_warn("Allocate new hctx on node %d fails, fallback to previous one on node %d\n",
+					node, old_node);
+			hctxs[i] = blk_mq_alloc_and_init_hctx(set, q, i,
+					old_node);
+			WARN_ON_ONCE(!hctxs[i]);
 		}
 	}
 	/*
-- 
2.31.1

Re: [PATCH 2/6] blk-mq: simplify reallocation of hw ctxs a bit

[Christoph Hellwig]

On Mon, Feb 28, 2022 at 05:04:26PM +0800, Ming Lei wrote:
> blk_mq_alloc_and_init_hctx() has already taken reuse into account, so
> no need to do it outside, then we can simplify blk_mq_realloc_hw_ctxs().

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

[PATCH 3/6] blk-mq: re-config poll after queue map is changed

[Ming Lei]

queue map can be changed when updating nr_hw_queues, so we need to
re-config queue's poll capability. Add one helper for doing this job.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 361903f07c84..5ce6a8289cff 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4010,6 +4010,17 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
 	mutex_unlock(&q->sysfs_lock);
 }
 
+static void blk_mq_config_poll(struct request_queue *q)
+{
+	struct blk_mq_tag_set *set = q->tag_set;
+
+	if (set->nr_maps > HCTX_TYPE_POLL &&
+	    set->map[HCTX_TYPE_POLL].nr_queues)
+		blk_queue_flag_set(QUEUE_FLAG_POLL, q);
+	else
+		blk_queue_flag_clear(QUEUE_FLAG_POLL, q);
+}
+
 int blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 		struct request_queue *q)
 {
@@ -4044,9 +4055,7 @@ int blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 	q->tag_set = set;
 
 	q->queue_flags |= QUEUE_FLAG_MQ_DEFAULT;
-	if (set->nr_maps > HCTX_TYPE_POLL &&
-	    set->map[HCTX_TYPE_POLL].nr_queues)
-		blk_queue_flag_set(QUEUE_FLAG_POLL, q);
+	blk_mq_config_poll(q);
 
 	INIT_DELAYED_WORK(&q->requeue_work, blk_mq_requeue_work);
 	INIT_LIST_HEAD(&q->requeue_list);
@@ -4512,6 +4521,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
 	blk_mq_update_queue_map(set);
 	list_for_each_entry(q, &set->tag_list, tag_set_list) {
 		blk_mq_realloc_hw_ctxs(set, q);
+		blk_mq_config_poll(q);
 		if (q->nr_hw_queues != set->nr_hw_queues) {
 			int i = prev_nr_hw_queues;
 
-- 
2.31.1

Re: [PATCH 3/6] blk-mq: re-config poll after queue map is changed

[Christoph Hellwig]

On Mon, Feb 28, 2022 at 05:04:27PM +0800, Ming Lei wrote:
> queue map can be changed when updating nr_hw_queues, so we need to
> re-config queue's poll capability. Add one helper for doing this job.

s/re-config/reconfigure/g

> +static void blk_mq_config_poll(struct request_queue *q)
> +{
> +	struct blk_mq_tag_set *set = q->tag_set;
> +
> +	if (set->nr_maps > HCTX_TYPE_POLL &&
> +	    set->map[HCTX_TYPE_POLL].nr_queues)
> +		blk_queue_flag_set(QUEUE_FLAG_POLL, q);
> +	else
> +		blk_queue_flag_clear(QUEUE_FLAG_POLL, q);
> +}

Maybe name this blk_mq_update_poll_flag?

[PATCH 4/6] block: mtip32xx: don't touch q->queue_hw_ctx

[Ming Lei]

q->queue_hw_ctx is really one blk-mq internal structure for retrieving
hctx via its index, not supposed to be used by drivers. Meantime drivers
can get the tags structure easily from tagset.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/block/mtip32xx/mtip32xx.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/block/mtip32xx/mtip32xx.c b/drivers/block/mtip32xx/mtip32xx.c
index cba956881d55..2d43ab5b5cc0 100644
--- a/drivers/block/mtip32xx/mtip32xx.c
+++ b/drivers/block/mtip32xx/mtip32xx.c
@@ -160,9 +160,7 @@ static bool mtip_check_surprise_removal(struct driver_data *dd)
 static struct mtip_cmd *mtip_cmd_from_tag(struct driver_data *dd,
 					  unsigned int tag)
 {
-	struct blk_mq_hw_ctx *hctx = dd->queue->queue_hw_ctx[0];
-
-	return blk_mq_rq_to_pdu(blk_mq_tag_to_rq(hctx->tags, tag));
+	return blk_mq_rq_to_pdu(blk_mq_tag_to_rq(dd->tags.tags[0], tag));
 }
 
 /*
-- 
2.31.1

Re: [PATCH 4/6] block: mtip32xx: don't touch q->queue_hw_ctx

[Christoph Hellwig]

On Mon, Feb 28, 2022 at 05:04:28PM +0800, Ming Lei wrote:
> q->queue_hw_ctx is really one blk-mq internal structure for retrieving
> hctx via its index, not supposed to be used by drivers. Meantime drivers
> can get the tags structure easily from tagset.

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

[PATCH 5/6] blk-mq: add helper of blk_mq_get_hctx to retrieve hctx via its index

[Ming Lei]

Prepare for managing hctx mapping via xarray by adding one helper of
blk_mq_get_hctx().

No functional change.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq-sysfs.c   | 2 +-
 block/blk-mq.c         | 4 ++--
 block/blk-mq.h         | 2 +-
 include/linux/blk-mq.h | 8 +++++++-
 4 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index 674786574075..22950e764536 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -279,7 +279,7 @@ int __blk_mq_register_dev(struct device *dev, struct request_queue *q)
 
 unreg:
 	while (--i >= 0)
-		blk_mq_unregister_hctx(q->queue_hw_ctx[i]);
+		blk_mq_unregister_hctx(blk_mq_get_hctx(q, i));
 
 	kobject_uevent(q->mq_kobj, KOBJ_REMOVE);
 	kobject_del(q->mq_kobj);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 5ce6a8289cff..d01c1693a3d4 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -71,7 +71,7 @@ static int blk_mq_poll_stats_bkt(const struct request *rq)
 static inline struct blk_mq_hw_ctx *blk_qc_to_hctx(struct request_queue *q,
 		blk_qc_t qc)
 {
-	return q->queue_hw_ctx[(qc & ~BLK_QC_T_INTERNAL) >> BLK_QC_T_SHIFT];
+	return blk_mq_get_hctx(q, (qc & ~BLK_QC_T_INTERNAL) >> BLK_QC_T_SHIFT);
 }
 
 static inline struct request *blk_qc_to_rq(struct blk_mq_hw_ctx *hctx,
@@ -573,7 +573,7 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
 	 * If not tell the caller that it should skip this queue.
 	 */
 	ret = -EXDEV;
-	data.hctx = q->queue_hw_ctx[hctx_idx];
+	data.hctx = blk_mq_get_hctx(q, hctx_idx);
 	if (!blk_mq_hw_queue_mapped(data.hctx))
 		goto out_queue_exit;
 	cpu = cpumask_first_and(data.hctx->cpumask, cpu_online_mask);
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 948791ea2a3e..804668457f88 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -83,7 +83,7 @@ static inline struct blk_mq_hw_ctx *blk_mq_map_queue_type(struct request_queue *
 							  enum hctx_type type,
 							  unsigned int cpu)
 {
-	return q->queue_hw_ctx[q->tag_set->map[type].mq_map[cpu]];
+	return blk_mq_get_hctx(q, q->tag_set->map[type].mq_map[cpu]);
 }
 
 static inline enum hctx_type blk_mq_get_hctx_type(unsigned int flags)
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 3a41d50b85d3..3d949b1968f3 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -916,9 +916,15 @@ static inline void *blk_mq_rq_to_pdu(struct request *rq)
 	return rq + 1;
 }
 
+static inline struct blk_mq_hw_ctx *blk_mq_get_hctx(struct request_queue *q,
+		unsigned int hctx_idx)
+{
+	return q->queue_hw_ctx[hctx_idx];
+}
+
 #define queue_for_each_hw_ctx(q, hctx, i)				\
 	for ((i) = 0; (i) < (q)->nr_hw_queues &&			\
-	     ({ hctx = (q)->queue_hw_ctx[i]; 1; }); (i)++)
+	     ({ hctx = blk_mq_get_hctx((q), (i)); 1; }); (i)++)
 
 #define hctx_for_each_ctx(hctx, ctx, i)					\
 	for ((i) = 0; (i) < (hctx)->nr_ctx &&				\
-- 
2.31.1

Re: [PATCH 5/6] blk-mq: add helper of blk_mq_get_hctx to retrieve hctx via its index

[Christoph Hellwig]

On Mon, Feb 28, 2022 at 05:04:29PM +0800, Ming Lei wrote:
> Prepare for managing hctx mapping via xarray by adding one helper of
> blk_mq_get_hctx().

I'd rather merge this into the next patch for reason I'll explain there.

[PATCH 6/6] blk-mq: manage hctx map via xarray

[Ming Lei]

Firstly code becomes more clean by switching to xarray from plain array.

Secondly use-after-free on q->queue_hw_ctx can be fixed because
queue_for_each_hw_ctx() may be run when updating nr_hw_queues is
in-progress. With this patch, q->hctx_table is defined as xarray, and
this structure will share same lifetime with request queue, so
queue_for_each_hw_ctx() can use q->hctx_table to lookup hctx reliably.

Reported-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq-tag.c     |  2 +-
 block/blk-mq.c         | 48 +++++++++++++++++-------------------------
 include/linux/blk-mq.h |  4 ++--
 include/linux/blkdev.h |  2 +-
 4 files changed, 23 insertions(+), 33 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 0fd409b8e86e..eb33667d63b2 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -498,7 +498,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_tag_iter_fn *fn,
 		void *priv)
 {
 	/*
-	 * __blk_mq_update_nr_hw_queues() updates nr_hw_queues and queue_hw_ctx
+	 * __blk_mq_update_nr_hw_queues() updates nr_hw_queues and hctx_table
 	 * while the queue is frozen. So we can use q_usage_counter to avoid
 	 * racing with it.
 	 */
diff --git a/block/blk-mq.c b/block/blk-mq.c
index d01c1693a3d4..273137dc3ffd 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3437,6 +3437,8 @@ static void blk_mq_exit_hctx(struct request_queue *q,
 
 	blk_mq_remove_cpuhp(hctx);
 
+	xa_erase(&q->hctx_table, hctx_idx);
+
 	spin_lock(&q->unused_hctx_lock);
 	list_add(&hctx->hctx_list, &q->unused_hctx_list);
 	spin_unlock(&q->unused_hctx_lock);
@@ -3476,8 +3478,15 @@ static int blk_mq_init_hctx(struct request_queue *q,
 	if (blk_mq_init_request(set, hctx->fq->flush_rq, hctx_idx,
 				hctx->numa_node))
 		goto exit_hctx;
+
+	if (xa_insert(&q->hctx_table, hctx_idx, hctx, GFP_KERNEL))
+		goto exit_flush_rq;
+
 	return 0;
 
+ exit_flush_rq:
+	if (set->ops->exit_request)
+		set->ops->exit_request(set, hctx->fq->flush_rq, hctx_idx);
  exit_hctx:
 	if (set->ops->exit_hctx)
 		set->ops->exit_hctx(hctx, hctx_idx);
@@ -3855,7 +3864,7 @@ void blk_mq_release(struct request_queue *q)
 		kobject_put(&hctx->kobj);
 	}
 
-	kfree(q->queue_hw_ctx);
+	xa_destroy(&q->hctx_table);
 
 	/*
 	 * release .mq_kobj and sw queue's kobject now because
@@ -3945,45 +3954,26 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
 						struct request_queue *q)
 {
 	int i, j, end;
-	struct blk_mq_hw_ctx **hctxs = q->queue_hw_ctx;
-
-	if (q->nr_hw_queues < set->nr_hw_queues) {
-		struct blk_mq_hw_ctx **new_hctxs;
-
-		new_hctxs = kcalloc_node(set->nr_hw_queues,
-				       sizeof(*new_hctxs), GFP_KERNEL,
-				       set->numa_node);
-		if (!new_hctxs)
-			return;
-		if (hctxs)
-			memcpy(new_hctxs, hctxs, q->nr_hw_queues *
-			       sizeof(*hctxs));
-		q->queue_hw_ctx = new_hctxs;
-		kfree(hctxs);
-		hctxs = new_hctxs;
-	}
 
 	/* protect against switching io scheduler  */
 	mutex_lock(&q->sysfs_lock);
 	for (i = 0; i < set->nr_hw_queues; i++) {
 		int old_node;
 		int node = blk_mq_get_hctx_node(set, i);
-		struct blk_mq_hw_ctx *old_hctx = hctxs[i];
+		struct blk_mq_hw_ctx *old_hctx = blk_mq_get_hctx(q, i);
 
 		if (old_hctx) {
 			old_node = old_hctx->numa_node;
 			blk_mq_exit_hctx(q, set, old_hctx, i);
 		}
 
-		hctxs[i] = blk_mq_alloc_and_init_hctx(set, q, i, node);
-		if (!hctxs[i]) {
+		if (!blk_mq_alloc_and_init_hctx(set, q, i, node)) {
 			if (!old_hctx)
 				break;
 			pr_warn("Allocate new hctx on node %d fails, fallback to previous one on node %d\n",
 					node, old_node);
-			hctxs[i] = blk_mq_alloc_and_init_hctx(set, q, i,
-					old_node);
-			WARN_ON_ONCE(!hctxs[i]);
+			WARN_ON_ONCE(!blk_mq_alloc_and_init_hctx(set, q, i,
+						old_node));
 		}
 	}
 	/*
@@ -4000,12 +3990,10 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
 	}
 
 	for (; j < end; j++) {
-		struct blk_mq_hw_ctx *hctx = hctxs[j];
+		struct blk_mq_hw_ctx *hctx = blk_mq_get_hctx(q, j);
 
-		if (hctx) {
+		if (hctx)
 			blk_mq_exit_hctx(q, set, hctx, j);
-			hctxs[j] = NULL;
-		}
 	}
 	mutex_unlock(&q->sysfs_lock);
 }
@@ -4045,6 +4033,8 @@ int blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 	INIT_LIST_HEAD(&q->unused_hctx_list);
 	spin_lock_init(&q->unused_hctx_lock);
 
+	xa_init(&q->hctx_table);
+
 	blk_mq_realloc_hw_ctxs(set, q);
 	if (!q->nr_hw_queues)
 		goto err_hctxs;
@@ -4074,7 +4064,7 @@ int blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 	return 0;
 
 err_hctxs:
-	kfree(q->queue_hw_ctx);
+	xa_destroy(&q->hctx_table);
 	q->nr_hw_queues = 0;
 	blk_mq_sysfs_deinit(q);
 err_poll:
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 3d949b1968f3..b102ff64e56a 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -919,12 +919,12 @@ static inline void *blk_mq_rq_to_pdu(struct request *rq)
 static inline struct blk_mq_hw_ctx *blk_mq_get_hctx(struct request_queue *q,
 		unsigned int hctx_idx)
 {
-	return q->queue_hw_ctx[hctx_idx];
+	return xa_load(&q->hctx_table, hctx_idx);
 }
 
 #define queue_for_each_hw_ctx(q, hctx, i)				\
 	for ((i) = 0; (i) < (q)->nr_hw_queues &&			\
-	     ({ hctx = blk_mq_get_hctx((q), (i)); 1; }); (i)++)
+	     (hctx = blk_mq_get_hctx((q), (i))); (i)++)
 
 #define hctx_for_each_ctx(hctx, ctx, i)					\
 	for ((i) = 0; (i) < (hctx)->nr_ctx &&				\
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index f757f9c2871f..a53ae40aaded 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -355,7 +355,7 @@ struct request_queue {
 	unsigned int		queue_depth;
 
 	/* hw dispatch queues */
-	struct blk_mq_hw_ctx	**queue_hw_ctx;
+	struct xarray		hctx_table;
 	unsigned int		nr_hw_queues;
 
 	/*
-- 
2.31.1

Re: [PATCH 6/6] blk-mq: manage hctx map via xarray

[kernel test robot]

Hi Ming,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on axboe-block/for-next]
[also build test WARNING on v5.17-rc6 next-20220225]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Ming-Lei/blk-mq-update_nr_hw_queues-related-improvement-bugfix/20220228-170706
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
config: alpha-allyesconfig (https://download.01.org/0day-ci/archive/20220301/202203010021.zTuzL2PG-lkp@intel.com/config)
compiler: alpha-linux-gcc (GCC) 11.2.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/176e39bc0acb20f8fd869d170b429b7253b089c4
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Ming-Lei/blk-mq-update_nr_hw_queues-related-improvement-bugfix/20220228-170706
        git checkout 176e39bc0acb20f8fd869d170b429b7253b089c4
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=alpha SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   In file included from block/blk-mq-debugfs-zoned.c:7:
>> block/blk-mq-debugfs.h:24:42: warning: 'struct blk_mq_hw_ctx' declared inside parameter list will not be visible outside of this definition or declaration
      24 |                                   struct blk_mq_hw_ctx *hctx);
         |                                          ^~~~~~~~~~~~~
   block/blk-mq-debugfs.h:25:44: warning: 'struct blk_mq_hw_ctx' declared inside parameter list will not be visible outside of this definition or declaration
      25 | void blk_mq_debugfs_unregister_hctx(struct blk_mq_hw_ctx *hctx);
         |                                            ^~~~~~~~~~~~~
   block/blk-mq-debugfs.h:32:47: warning: 'struct blk_mq_hw_ctx' declared inside parameter list will not be visible outside of this definition or declaration
      32 |                                        struct blk_mq_hw_ctx *hctx);
         |                                               ^~~~~~~~~~~~~
   block/blk-mq-debugfs.h:33:50: warning: 'struct blk_mq_hw_ctx' declared inside parameter list will not be visible outside of this definition or declaration
      33 | void blk_mq_debugfs_unregister_sched_hctx(struct blk_mq_hw_ctx *hctx);
         |                                                  ^~~~~~~~~~~~~


vim +24 block/blk-mq-debugfs.h

16b738f651c83a0 Omar Sandoval      2017-05-04  20  
6cfc0081b046ebf Greg Kroah-Hartman 2019-06-12  21  void blk_mq_debugfs_register(struct request_queue *q);
d173a25165c1244 Omar Sandoval      2017-05-04  22  void blk_mq_debugfs_unregister(struct request_queue *q);
6cfc0081b046ebf Greg Kroah-Hartman 2019-06-12  23  void blk_mq_debugfs_register_hctx(struct request_queue *q,
9c1051aacde8280 Omar Sandoval      2017-05-04 @24  				  struct blk_mq_hw_ctx *hctx);
9c1051aacde8280 Omar Sandoval      2017-05-04  25  void blk_mq_debugfs_unregister_hctx(struct blk_mq_hw_ctx *hctx);
6cfc0081b046ebf Greg Kroah-Hartman 2019-06-12  26  void blk_mq_debugfs_register_hctxs(struct request_queue *q);
9c1051aacde8280 Omar Sandoval      2017-05-04  27  void blk_mq_debugfs_unregister_hctxs(struct request_queue *q);
d332ce091813d11 Omar Sandoval      2017-05-04  28  

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

Re: [PATCH 6/6] blk-mq: manage hctx map via xarray

[kernel test robot]

Hi Ming,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on axboe-block/for-next]
[also build test WARNING on v5.17-rc6 next-20220225]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Ming-Lei/blk-mq-update_nr_hw_queues-related-improvement-bugfix/20220228-170706
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
config: i386-randconfig-a002-20220228 (https://download.01.org/0day-ci/archive/20220301/202203010133.JIpKpP2Z-lkp@intel.com/config)
compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project d271fc04d5b97b12e6b797c6067d3c96a8d7470e)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/176e39bc0acb20f8fd869d170b429b7253b089c4
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Ming-Lei/blk-mq-update_nr_hw_queues-related-improvement-bugfix/20220228-170706
        git checkout 176e39bc0acb20f8fd869d170b429b7253b089c4
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   In file included from block/blk-mq-debugfs-zoned.c:7:
>> block/blk-mq-debugfs.h:24:14: warning: declaration of 'struct blk_mq_hw_ctx' will not be visible outside of this function [-Wvisibility]
                                     struct blk_mq_hw_ctx *hctx);
                                            ^
   block/blk-mq-debugfs.h:25:44: warning: declaration of 'struct blk_mq_hw_ctx' will not be visible outside of this function [-Wvisibility]
   void blk_mq_debugfs_unregister_hctx(struct blk_mq_hw_ctx *hctx);
                                              ^
   block/blk-mq-debugfs.h:32:19: warning: declaration of 'struct blk_mq_hw_ctx' will not be visible outside of this function [-Wvisibility]
                                          struct blk_mq_hw_ctx *hctx);
                                                 ^
   block/blk-mq-debugfs.h:33:50: warning: declaration of 'struct blk_mq_hw_ctx' will not be visible outside of this function [-Wvisibility]
   void blk_mq_debugfs_unregister_sched_hctx(struct blk_mq_hw_ctx *hctx);
                                                    ^
   4 warnings generated.


vim +24 block/blk-mq-debugfs.h

16b738f651c83a Omar Sandoval      2017-05-04  20  
6cfc0081b046eb Greg Kroah-Hartman 2019-06-12  21  void blk_mq_debugfs_register(struct request_queue *q);
d173a25165c124 Omar Sandoval      2017-05-04  22  void blk_mq_debugfs_unregister(struct request_queue *q);
6cfc0081b046eb Greg Kroah-Hartman 2019-06-12  23  void blk_mq_debugfs_register_hctx(struct request_queue *q,
9c1051aacde828 Omar Sandoval      2017-05-04 @24  				  struct blk_mq_hw_ctx *hctx);
9c1051aacde828 Omar Sandoval      2017-05-04  25  void blk_mq_debugfs_unregister_hctx(struct blk_mq_hw_ctx *hctx);
6cfc0081b046eb Greg Kroah-Hartman 2019-06-12  26  void blk_mq_debugfs_register_hctxs(struct request_queue *q);
9c1051aacde828 Omar Sandoval      2017-05-04  27  void blk_mq_debugfs_unregister_hctxs(struct request_queue *q);
d332ce091813d1 Omar Sandoval      2017-05-04  28  

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

Re: [PATCH 6/6] blk-mq: manage hctx map via xarray

[Ming Lei]

Hi,

Thanks for the report!

On Tue, Mar 01, 2022 at 01:57:33AM +0800, kernel test robot wrote:
> Hi Ming,
> 
> Thank you for the patch! Perhaps something to improve:
> 
> [auto build test WARNING on axboe-block/for-next]
> [also build test WARNING on v5.17-rc6 next-20220225]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch]
> 
> url:    https://github.com/0day-ci/linux/commits/Ming-Lei/blk-mq-update_nr_hw_queues-related-improvement-bugfix/20220228-170706
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
> config: i386-randconfig-a002-20220228 (https://download.01.org/0day-ci/archive/20220301/202203010133.JIpKpP2Z-lkp@intel.com/config)
> compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project d271fc04d5b97b12e6b797c6067d3c96a8d7470e)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://github.com/0day-ci/linux/commit/176e39bc0acb20f8fd869d170b429b7253b089c4
>         git remote add linux-review https://github.com/0day-ci/linux
>         git fetch --no-tags linux-review Ming-Lei/blk-mq-update_nr_hw_queues-related-improvement-bugfix/20220228-170706
>         git checkout 176e39bc0acb20f8fd869d170b429b7253b089c4
>         # save the config file to linux build tree
>         mkdir build_dir
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
> 
> All warnings (new ones prefixed by >>):
> 
>    In file included from block/blk-mq-debugfs-zoned.c:7:
> >> block/blk-mq-debugfs.h:24:14: warning: declaration of 'struct blk_mq_hw_ctx' will not be visible outside of this function [-Wvisibility]
>                                      struct blk_mq_hw_ctx *hctx);


The warning is nothing to do with this patchset.

You can trigger that by just changing modify time of include/linux/blkdev.h.

The following patch can fix the warning, and I will post one formal
patch soon.

diff --git a/block/blk-mq-debugfs.h b/block/blk-mq-debugfs.h
index a68aa6041a10..37fe2716e96e 100644
--- a/block/blk-mq-debugfs.h
+++ b/block/blk-mq-debugfs.h
@@ -5,6 +5,7 @@
 #ifdef CONFIG_BLK_DEBUG_FS

 #include <linux/seq_file.h>
+#include <linux/blk-mq.h>

 struct blk_mq_debugfs_attr {
        const char *name;


Thanks,
Ming

Re: [PATCH 6/6] blk-mq: manage hctx map via xarray

[Ming Lei]

[-- Attachment #1: Type: text/plain, Size: 2698 bytes --]

Hi,

Thanks for the report!

On Tue, Mar 01, 2022 at 01:57:33AM +0800, kernel test robot wrote:
> Hi Ming,
> 
> Thank you for the patch! Perhaps something to improve:
> 
> [auto build test WARNING on axboe-block/for-next]
> [also build test WARNING on v5.17-rc6 next-20220225]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch]
> 
> url:    https://github.com/0day-ci/linux/commits/Ming-Lei/blk-mq-update_nr_hw_queues-related-improvement-bugfix/20220228-170706
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
> config: i386-randconfig-a002-20220228 (https://download.01.org/0day-ci/archive/20220301/202203010133.JIpKpP2Z-lkp(a)intel.com/config)
> compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project d271fc04d5b97b12e6b797c6067d3c96a8d7470e)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://github.com/0day-ci/linux/commit/176e39bc0acb20f8fd869d170b429b7253b089c4
>         git remote add linux-review https://github.com/0day-ci/linux
>         git fetch --no-tags linux-review Ming-Lei/blk-mq-update_nr_hw_queues-related-improvement-bugfix/20220228-170706
>         git checkout 176e39bc0acb20f8fd869d170b429b7253b089c4
>         # save the config file to linux build tree
>         mkdir build_dir
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
> 
> All warnings (new ones prefixed by >>):
> 
>    In file included from block/blk-mq-debugfs-zoned.c:7:
> >> block/blk-mq-debugfs.h:24:14: warning: declaration of 'struct blk_mq_hw_ctx' will not be visible outside of this function [-Wvisibility]
>                                      struct blk_mq_hw_ctx *hctx);


The warning is nothing to do with this patchset.

You can trigger that by just changing modify time of include/linux/blkdev.h.

The following patch can fix the warning, and I will post one formal
patch soon.

diff --git a/block/blk-mq-debugfs.h b/block/blk-mq-debugfs.h
index a68aa6041a10..37fe2716e96e 100644
--- a/block/blk-mq-debugfs.h
+++ b/block/blk-mq-debugfs.h
@@ -5,6 +5,7 @@
 #ifdef CONFIG_BLK_DEBUG_FS

 #include <linux/seq_file.h>
+#include <linux/blk-mq.h>

 struct blk_mq_debugfs_attr {
        const char *name;


Thanks,
Ming

Re: [PATCH 6/6] blk-mq: manage hctx map via xarray

[Christoph Hellwig]

> -			hctxs[i] = blk_mq_alloc_and_init_hctx(set, q, i,
> -					old_node);
> -			WARN_ON_ONCE(!hctxs[i]);
> +			WARN_ON_ONCE(!blk_mq_alloc_and_init_hctx(set, q, i,
> +						old_node));


Please avoid doing the actual work inside a WARN_ON statement.

>  
>  	for (; j < end; j++) {
> -		struct blk_mq_hw_ctx *hctx = hctxs[j];
> +		struct blk_mq_hw_ctx *hctx = blk_mq_get_hctx(q, j);
>  
> -		if (hctx) {
> +		if (hctx)
>  			blk_mq_exit_hctx(q, set, hctx, j);
> -			hctxs[j] = NULL;
> -		}
>  	}

Instead of a for loop that does xa_loads repeatedly this can just
use xa_for_each_range.  Same for a bunch of other loops like that,
e.g. in blk_mq_unregister_dev or the __blk_mq_register_dev failure
path.

> @@ -919,12 +919,12 @@ static inline void *blk_mq_rq_to_pdu(struct request *rq)
>  static inline struct blk_mq_hw_ctx *blk_mq_get_hctx(struct request_queue *q,
>  		unsigned int hctx_idx)
>  {
> -	return q->queue_hw_ctx[hctx_idx];
> +	return xa_load(&q->hctx_table, hctx_idx);
>  }
>  
>  #define queue_for_each_hw_ctx(q, hctx, i)				\
>  	for ((i) = 0; (i) < (q)->nr_hw_queues &&			\
> -	     ({ hctx = blk_mq_get_hctx((q), (i)); 1; }); (i)++)
> +	     (hctx = blk_mq_get_hctx((q), (i))); (i)++)

This should be using a xa_for_each loop.

With various places converted to loops I'm not even sure we really
want the blk_mq_get_hctx helper at all.

Re: [PATCH 6/6] blk-mq: manage hctx map via xarray

[Ming Lei]

On Tue, Mar 01, 2022 at 05:37:17AM -0800, Christoph Hellwig wrote:
> > -			hctxs[i] = blk_mq_alloc_and_init_hctx(set, q, i,
> > -					old_node);
> > -			WARN_ON_ONCE(!hctxs[i]);
> > +			WARN_ON_ONCE(!blk_mq_alloc_and_init_hctx(set, q, i,
> > +						old_node));
> 
> 
> Please avoid doing the actual work inside a WARN_ON statement.

OK.

> 
> >  
> >  	for (; j < end; j++) {
> > -		struct blk_mq_hw_ctx *hctx = hctxs[j];
> > +		struct blk_mq_hw_ctx *hctx = blk_mq_get_hctx(q, j);
> >  
> > -		if (hctx) {
> > +		if (hctx)
> >  			blk_mq_exit_hctx(q, set, hctx, j);
> > -			hctxs[j] = NULL;
> > -		}
> >  	}
> 
> Instead of a for loop that does xa_loads repeatedly this can just
> use xa_for_each_range.  Same for a bunch of other loops like that,
> e.g. in blk_mq_unregister_dev or the __blk_mq_register_dev failure
> path.
> 
> > @@ -919,12 +919,12 @@ static inline void *blk_mq_rq_to_pdu(struct request *rq)
> >  static inline struct blk_mq_hw_ctx *blk_mq_get_hctx(struct request_queue *q,
> >  		unsigned int hctx_idx)
> >  {
> > -	return q->queue_hw_ctx[hctx_idx];
> > +	return xa_load(&q->hctx_table, hctx_idx);
> >  }
> >  
> >  #define queue_for_each_hw_ctx(q, hctx, i)				\
> >  	for ((i) = 0; (i) < (q)->nr_hw_queues &&			\
> > -	     ({ hctx = blk_mq_get_hctx((q), (i)); 1; }); (i)++)
> > +	     (hctx = blk_mq_get_hctx((q), (i))); (i)++)
> 
> This should be using a xa_for_each loop.

I did considered xa_for_each(), but it requires rcu read lock.

Also queue_for_each_hw_ctx() is supposed to not run in fast path,
meantime xa_load() is lightweight enough too, so repeated xa_load()
is fine here.


Thanks,
Ming

Re: [PATCH 6/6] blk-mq: manage hctx map via xarray

[Christoph Hellwig]

On Wed, Mar 02, 2022 at 10:06:04AM +0800, Ming Lei wrote:
> I did considered xa_for_each(), but it requires rcu read lock.

No, I doesn't.  It just takes a RCU lock internally.

> Also queue_for_each_hw_ctx() is supposed to not run in fast path,
> meantime xa_load() is lightweight enough too, so repeated xa_load()
> is fine here.

I'd rather have the clarity of the proper iterators.

Re: [PATCH 6/6] blk-mq: manage hctx map via xarray

[Ming Lei]

On Wed, Mar 02, 2022 at 12:24:34AM -0800, Christoph Hellwig wrote:
> On Wed, Mar 02, 2022 at 10:06:04AM +0800, Ming Lei wrote:
> > I did considered xa_for_each(), but it requires rcu read lock.
> 
> No, I doesn't.  It just takes a RCU lock internally.

OK.

> 
> > Also queue_for_each_hw_ctx() is supposed to not run in fast path,
> > meantime xa_load() is lightweight enough too, so repeated xa_load()
> > is fine here.
> 
> I'd rather have the clarity of the proper iterators.
 
Another point is that 'unsigned long *' is passed to xa_find() as index.
However, almost all users of queue_for_each_hw_ctx() defines hctx index
as 'unsigned int'.

If we switch to xa_for_each(), the type of hctx index needs to be changed
to 'unsigned long' for every queue_for_each_hw_ctx(). But xa_load()
needn't such change.

Also from user viewpoint, looks 'unsigned long' change for hctx index is
still a bit confusing, IMO.


Thanks,
Ming

Re: [PATCH 6/6] blk-mq: manage hctx map via xarray

[Christoph Hellwig]

On Wed, Mar 02, 2022 at 05:53:44PM +0800, Ming Lei wrote:
> Another point is that 'unsigned long *' is passed to xa_find() as index.
> However, almost all users of queue_for_each_hw_ctx() defines hctx index
> as 'unsigned int'.
> 
> If we switch to xa_for_each(), the type of hctx index needs to be changed
> to 'unsigned long' for every queue_for_each_hw_ctx(). But xa_load()
> needn't such change.
> 
> Also from user viewpoint, looks 'unsigned long' change for hctx index is
> still a bit confusing, IMO.

If you use xarray you need to fit the convention it expects, that should
not be in any way a surprise.