[PATCH 0/2] nvme: fix regression with MD RAID

[PATCH 0/2] nvme: fix regression with MD RAID

[Hannes Reinecke]

Hi all,

ever since the implementation NVMe-oF does not work together with MD RAID.
MD RAID expects the device to return an I/O error on failure, and to remove
the block device if the underlying hardware is removed.
This is contrary to the implementation of NVMe-oF, which will keep on retrying
I/O while the controller is being reset, and will only remove the block device
once the last _user_ is gone.

These patches fixup this situation by adding a new sysfs attribute
'fail_if_no_path'. When this attribute is set we will return I/O errors
as soon as no paths are available anymore, and will remove the block device
once the last controller holding a path to the namespace is removed (ie after
all reconnect attempts for that controllers are exhausted).

This is a rework of the earlier path by Keith Busch ('nvme-mpath: delete disk
after last connection'). Kudos to him for suggesting this approach.

Hannes Reinecke (2):
  nvme: add 'fail_if_no_path' sysfs attribute
  nvme: delete disk when last path is gone

 drivers/nvme/host/core.c      |  6 +++++
 drivers/nvme/host/multipath.c | 46 ++++++++++++++++++++++++++++++++---
 drivers/nvme/host/nvme.h      | 19 +++++++++++++--
 3 files changed, 66 insertions(+), 5 deletions(-)

-- 
2.29.2


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[PATCH 1/2] nvme: add 'fail_if_no_path' sysfs attribute

[Hannes Reinecke]

In some setups like RAID or cluster we need to return an I/O error
once all paths are unavailable to allow the upper layers to start
their own error recovery (like redirecting I/O to other mirrors).
This patch adds a sysfs attribute 'fail_if_no_path' to allow the
admin to enable that behaviour instead of the current 'queue until
a path becomes available' policy.

Signed-off-by: Hannes Reinecke <hare@suse.de>
---
 drivers/nvme/host/core.c      |  5 ++++
 drivers/nvme/host/multipath.c | 43 +++++++++++++++++++++++++++++++++--
 drivers/nvme/host/nvme.h      |  2 ++
 3 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 4de6a3a13575..2fb3ecc0c53b 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3464,6 +3464,7 @@ static struct attribute *nvme_ns_id_attrs[] = {
 #ifdef CONFIG_NVME_MULTIPATH
 	&dev_attr_ana_grpid.attr,
 	&dev_attr_ana_state.attr,
+	&dev_attr_fail_if_no_path.attr,
 #endif
 	NULL,
 };
@@ -3494,6 +3495,10 @@ static umode_t nvme_ns_id_attrs_are_visible(struct kobject *kobj,
 		if (!nvme_ctrl_use_ana(nvme_get_ns_from_dev(dev)->ctrl))
 			return 0;
 	}
+	if (a == &dev_attr_fail_if_no_path.attr) {
+		if (dev_to_disk(dev)->fops == &nvme_bdev_ops)
+			return 0;
+	}
 #endif
 	return a->mode;
 }
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 0696319adaf6..d5773ea105b1 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -283,10 +283,18 @@ static bool nvme_available_path(struct nvme_ns_head *head)
 			continue;
 		switch (ns->ctrl->state) {
 		case NVME_CTRL_LIVE:
+			if (!test_bit(NVME_NSHEAD_FAIL_IF_NO_PATH,
+				      &head->flags))
+				return true;
+			if (ns->ana_state != NVME_ANA_INACCESSIBLE &&
+			    ns->ana_state != NVME_ANA_PERSISTENT_LOSS)
+				return true;
 		case NVME_CTRL_RESETTING:
-		case NVME_CTRL_CONNECTING:
 			/* fallthru */
-			return true;
+		case NVME_CTRL_CONNECTING:
+			if (!test_bit(NVME_NSHEAD_FAIL_IF_NO_PATH,
+				      &head->flags))
+				return true;
 		default:
 			break;
 		}
@@ -641,6 +649,37 @@ static ssize_t ana_state_show(struct device *dev, struct device_attribute *attr,
 }
 DEVICE_ATTR_RO(ana_state);
 
+static ssize_t fail_if_no_path_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct gendisk *disk = dev_to_disk(dev);
+	struct nvme_ns_head *head = disk->private_data;
+
+	return sprintf(buf, "%d\n",
+		       test_bit(NVME_NSHEAD_FAIL_IF_NO_PATH, &head->flags) ?
+		       1 : 0);
+}
+
+static ssize_t fail_if_no_path_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct gendisk *disk = dev_to_disk(dev);
+	struct nvme_ns_head *head = disk->private_data;
+	int fail_if_no_path, err;
+
+	err = kstrtoint(buf, 10, &fail_if_no_path);
+	if (err)
+		return -EINVAL;
+
+	if (fail_if_no_path <= 0)
+		clear_bit(NVME_NSHEAD_FAIL_IF_NO_PATH, &head->flags);
+	else
+		set_bit(NVME_NSHEAD_FAIL_IF_NO_PATH, &head->flags);
+	return count;
+}
+DEVICE_ATTR(fail_if_no_path, S_IRUGO | S_IWUSR,
+	fail_if_no_path_show, fail_if_no_path_store);
+
 static int nvme_lookup_ana_group_desc(struct nvme_ctrl *ctrl,
 		struct nvme_ana_group_desc *desc, void *data)
 {
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 07b34175c6ce..3d2513f8194d 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -418,6 +418,7 @@ struct nvme_ns_head {
 	struct mutex		lock;
 	unsigned long		flags;
 #define NVME_NSHEAD_DISK_LIVE	0
+#define NVME_NSHEAD_FAIL_IF_NO_PATH	1
 	struct nvme_ns __rcu	*current_path[];
 #endif
 };
@@ -694,6 +695,7 @@ static inline void nvme_trace_bio_complete(struct request *req)
 
 extern struct device_attribute dev_attr_ana_grpid;
 extern struct device_attribute dev_attr_ana_state;
+extern struct device_attribute dev_attr_fail_if_no_path;
 extern struct device_attribute subsys_attr_iopolicy;
 
 #else
-- 
2.29.2


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[PATCH 2/2] nvme: delete disk when last path is gone

[Hannes Reinecke]

The multipath code currently deletes the disk only after all references
to it are dropped rather than when the last path to that disk is lost.
This has been reported to cause problems with some use cases like MD RAID.

This patch implements an alternative behaviour of deleting the disk when
the last path is gone, ie the same behaviour as non-multipathed nvme
devices. The new behaviour will be selected with the 'fail_if_no_path'
attribute, as returning it's arguably the same functionality.

Suggested-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Hannes Reinecke <hare@suse.de>
---
 drivers/nvme/host/core.c      |  1 +
 drivers/nvme/host/multipath.c |  3 ++-
 drivers/nvme/host/nvme.h      | 17 +++++++++++++++--
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 2fb3ecc0c53b..d717a6283d6e 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -542,6 +542,7 @@ static void nvme_free_ns_head(struct kref *ref)
 		container_of(ref, struct nvme_ns_head, ref);
 
 	nvme_mpath_remove_disk(head);
+	nvme_mpath_put_disk(head);
 	ida_simple_remove(&head->subsys->ns_ida, head->instance);
 	cleanup_srcu_struct(&head->srcu);
 	nvme_put_subsystem(head->subsys);
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index d5773ea105b1..f995b8234622 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -724,6 +724,8 @@ void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id)
 
 void nvme_mpath_remove_disk(struct nvme_ns_head *head)
 {
+	if (test_bit(NVME_NSHEAD_FAIL_IF_NO_PATH, &head->flags))
+		return;
 	if (!head->disk)
 		return;
 	if (head->disk->flags & GENHD_FL_UP)
@@ -741,7 +743,6 @@ void nvme_mpath_remove_disk(struct nvme_ns_head *head)
 		 */
 		head->disk->queue = NULL;
 	}
-	put_disk(head->disk);
 }
 
 int nvme_mpath_init(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 3d2513f8194d..e6efa085f08a 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -681,8 +681,12 @@ static inline void nvme_mpath_check_last_path(struct nvme_ns *ns)
 {
 	struct nvme_ns_head *head = ns->head;
 
-	if (head->disk && list_empty(&head->list))
-		kblockd_schedule_work(&head->requeue_work);
+	if (head->disk && list_empty(&head->list)) {
+		if (test_bit(NVME_NSHEAD_FAIL_IF_NO_PATH, &head->flags))
+			nvme_mpath_remove_disk(head);
+		else
+			kblockd_schedule_work(&head->requeue_work);
+	}
 }
 
 static inline void nvme_trace_bio_complete(struct request *req)
@@ -693,6 +697,12 @@ static inline void nvme_trace_bio_complete(struct request *req)
 		trace_block_bio_complete(ns->head->disk->queue, req->bio);
 }
 
+static inline void nvme_mpath_put_disk(struct nvme_ns_head *head)
+{
+	if (head->disk)
+		put_disk(head->disk);
+}
+
 extern struct device_attribute dev_attr_ana_grpid;
 extern struct device_attribute dev_attr_ana_state;
 extern struct device_attribute dev_attr_fail_if_no_path;
@@ -731,6 +741,9 @@ static inline void nvme_mpath_add_disk(struct nvme_ns *ns,
 static inline void nvme_mpath_remove_disk(struct nvme_ns_head *head)
 {
 }
+static inline void nvme_mpath_put_disk(struct nvme_ns_head *head)
+{
+}
 static inline bool nvme_mpath_clear_current_path(struct nvme_ns *ns)
 {
 	return false;
-- 
2.29.2


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Re: [PATCH 1/2] nvme: add 'fail_if_no_path' sysfs attribute

[Minwoo Im]

On 21-02-23 12:59:21, Hannes Reinecke wrote:
> In some setups like RAID or cluster we need to return an I/O error
> once all paths are unavailable to allow the upper layers to start
> their own error recovery (like redirecting I/O to other mirrors).
> This patch adds a sysfs attribute 'fail_if_no_path' to allow the
> admin to enable that behaviour instead of the current 'queue until
> a path becomes available' policy.
> 
> Signed-off-by: Hannes Reinecke <hare@suse.de>
> ---
>  drivers/nvme/host/core.c      |  5 ++++
>  drivers/nvme/host/multipath.c | 43 +++++++++++++++++++++++++++++++++--
>  drivers/nvme/host/nvme.h      |  2 ++
>  3 files changed, 48 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 4de6a3a13575..2fb3ecc0c53b 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -3464,6 +3464,7 @@ static struct attribute *nvme_ns_id_attrs[] = {
>  #ifdef CONFIG_NVME_MULTIPATH
>  	&dev_attr_ana_grpid.attr,
>  	&dev_attr_ana_state.attr,
> +	&dev_attr_fail_if_no_path.attr,
>  #endif
>  	NULL,
>  };
> @@ -3494,6 +3495,10 @@ static umode_t nvme_ns_id_attrs_are_visible(struct kobject *kobj,
>  		if (!nvme_ctrl_use_ana(nvme_get_ns_from_dev(dev)->ctrl))
>  			return 0;
>  	}
> +	if (a == &dev_attr_fail_if_no_path.attr) {
> +		if (dev_to_disk(dev)->fops == &nvme_bdev_ops)
> +			return 0;
> +	}
>  #endif
>  	return a->mode;
>  }
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index 0696319adaf6..d5773ea105b1 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -283,10 +283,18 @@ static bool nvme_available_path(struct nvme_ns_head *head)
>  			continue;
>  		switch (ns->ctrl->state) {
>  		case NVME_CTRL_LIVE:
> +			if (!test_bit(NVME_NSHEAD_FAIL_IF_NO_PATH,
> +				      &head->flags))
> +				return true;
> +			if (ns->ana_state != NVME_ANA_INACCESSIBLE &&
> +			    ns->ana_state != NVME_ANA_PERSISTENT_LOSS)
> +				return true;

It looks like it needs to prevent fallthru here with return false.  It
causes following warning:

  drivers/nvme/host/multipath.c: In function ‘nvme_available_path’:
  drivers/nvme/host/multipath.c:289:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
    289 |    if (ns->ana_state != NVME_ANA_INACCESSIBLE &&
        |       ^
  drivers/nvme/host/multipath.c:292:3: note: here
    292 |   case NVME_CTRL_RESETTING:
        |   ^~~~


diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index f995b8234622..d692eab3d483 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -289,6 +289,7 @@ static bool nvme_available_path(struct nvme_ns_head *head)
                        if (ns->ana_state != NVME_ANA_INACCESSIBLE &&
                            ns->ana_state != NVME_ANA_PERSISTENT_LOSS)
                                return true;
+                       return false;
                case NVME_CTRL_RESETTING:

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Re: [PATCH 2/2] nvme: delete disk when last path is gone

[Minwoo Im]

On 21-02-23 12:59:22, Hannes Reinecke wrote:
> The multipath code currently deletes the disk only after all references
> to it are dropped rather than when the last path to that disk is lost.
> This has been reported to cause problems with some use cases like MD RAID.
> 
> This patch implements an alternative behaviour of deleting the disk when
> the last path is gone, ie the same behaviour as non-multipathed nvme
> devices. The new behaviour will be selected with the 'fail_if_no_path'
> attribute, as returning it's arguably the same functionality.
> 
> Suggested-by: Keith Busch <kbusch@kernel.org>
> Signed-off-by: Hannes Reinecke <hare@suse.de>
> ---
>  drivers/nvme/host/core.c      |  1 +
>  drivers/nvme/host/multipath.c |  3 ++-
>  drivers/nvme/host/nvme.h      | 17 +++++++++++++++--
>  3 files changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 2fb3ecc0c53b..d717a6283d6e 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -542,6 +542,7 @@ static void nvme_free_ns_head(struct kref *ref)
>  		container_of(ref, struct nvme_ns_head, ref);
>  
>  	nvme_mpath_remove_disk(head);
> +	nvme_mpath_put_disk(head);
>  	ida_simple_remove(&head->subsys->ns_ida, head->instance);
>  	cleanup_srcu_struct(&head->srcu);
>  	nvme_put_subsystem(head->subsys);
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index d5773ea105b1..f995b8234622 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -724,6 +724,8 @@ void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id)
>  
>  void nvme_mpath_remove_disk(struct nvme_ns_head *head)
>  {
> +	if (test_bit(NVME_NSHEAD_FAIL_IF_NO_PATH, &head->flags))
> +		return;
>  	if (!head->disk)
>  		return;
>  	if (head->disk->flags & GENHD_FL_UP)
> @@ -741,7 +743,6 @@ void nvme_mpath_remove_disk(struct nvme_ns_head *head)
>  		 */
>  		head->disk->queue = NULL;
>  	}
> -	put_disk(head->disk);
>  }
>  
>  int nvme_mpath_init(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
> index 3d2513f8194d..e6efa085f08a 100644
> --- a/drivers/nvme/host/nvme.h
> +++ b/drivers/nvme/host/nvme.h
> @@ -681,8 +681,12 @@ static inline void nvme_mpath_check_last_path(struct nvme_ns *ns)
>  {
>  	struct nvme_ns_head *head = ns->head;
>  
> -	if (head->disk && list_empty(&head->list))
> -		kblockd_schedule_work(&head->requeue_work);
> +	if (head->disk && list_empty(&head->list)) {
> +		if (test_bit(NVME_NSHEAD_FAIL_IF_NO_PATH, &head->flags))
> +			nvme_mpath_remove_disk(head);

Does it need to call nvme_mpath_remove_disk here ?  It looks like it
returns with nothing right away if NVME_NSHEAD_FAIL_IF_NO_PATH is set.

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Re: [PATCH 2/2] nvme: delete disk when last path is gone

[Hannes Reinecke]

On 2/23/21 1:56 PM, Minwoo Im wrote:
> On 21-02-23 12:59:22, Hannes Reinecke wrote:
>> The multipath code currently deletes the disk only after all references
>> to it are dropped rather than when the last path to that disk is lost.
>> This has been reported to cause problems with some use cases like MD RAID.
>>
>> This patch implements an alternative behaviour of deleting the disk when
>> the last path is gone, ie the same behaviour as non-multipathed nvme
>> devices. The new behaviour will be selected with the 'fail_if_no_path'
>> attribute, as returning it's arguably the same functionality.
>>
>> Suggested-by: Keith Busch <kbusch@kernel.org>
>> Signed-off-by: Hannes Reinecke <hare@suse.de>
>> ---
>>  drivers/nvme/host/core.c      |  1 +
>>  drivers/nvme/host/multipath.c |  3 ++-
>>  drivers/nvme/host/nvme.h      | 17 +++++++++++++++--
>>  3 files changed, 18 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
>> index 2fb3ecc0c53b..d717a6283d6e 100644
>> --- a/drivers/nvme/host/core.c
>> +++ b/drivers/nvme/host/core.c
>> @@ -542,6 +542,7 @@ static void nvme_free_ns_head(struct kref *ref)
>>  		container_of(ref, struct nvme_ns_head, ref);
>>  
>>  	nvme_mpath_remove_disk(head);
>> +	nvme_mpath_put_disk(head);
>>  	ida_simple_remove(&head->subsys->ns_ida, head->instance);
>>  	cleanup_srcu_struct(&head->srcu);
>>  	nvme_put_subsystem(head->subsys);
>> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
>> index d5773ea105b1..f995b8234622 100644
>> --- a/drivers/nvme/host/multipath.c
>> +++ b/drivers/nvme/host/multipath.c
>> @@ -724,6 +724,8 @@ void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id)
>>  
>>  void nvme_mpath_remove_disk(struct nvme_ns_head *head)
>>  {
>> +	if (test_bit(NVME_NSHEAD_FAIL_IF_NO_PATH, &head->flags))
>> +		return;
>>  	if (!head->disk)
>>  		return;
>>  	if (head->disk->flags & GENHD_FL_UP)
>> @@ -741,7 +743,6 @@ void nvme_mpath_remove_disk(struct nvme_ns_head *head)
>>  		 */
>>  		head->disk->queue = NULL;
>>  	}
>> -	put_disk(head->disk);
>>  }
>>  
>>  int nvme_mpath_init(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
>> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
>> index 3d2513f8194d..e6efa085f08a 100644
>> --- a/drivers/nvme/host/nvme.h
>> +++ b/drivers/nvme/host/nvme.h
>> @@ -681,8 +681,12 @@ static inline void nvme_mpath_check_last_path(struct nvme_ns *ns)
>>  {
>>  	struct nvme_ns_head *head = ns->head;
>>  
>> -	if (head->disk && list_empty(&head->list))
>> -		kblockd_schedule_work(&head->requeue_work);
>> +	if (head->disk && list_empty(&head->list)) {
>> +		if (test_bit(NVME_NSHEAD_FAIL_IF_NO_PATH, &head->flags))
>> +			nvme_mpath_remove_disk(head);
> 
> Does it need to call nvme_mpath_remove_disk here ?  It looks like it
> returns with nothing right away if NVME_NSHEAD_FAIL_IF_NO_PATH is set.
> 
Argl. Yes, you are correct.

I'll be reworking that one.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@suse.de			                  +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Felix Imendörffer

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Re: [PATCH 0/2] nvme: fix regression with MD RAID

[Christoph Hellwig]

I don't see any regression here, even if the new features sound useful.

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Re: [PATCH 0/2] nvme: fix regression with MD RAID

[Hannes Reinecke]

On 2/24/21 5:25 PM, Christoph Hellwig wrote:
> I don't see any regression here, even if the new features sound useful.
> 
Have you ever tried MD RAID on nvme-of?
Without this patch MD RAID will _stop_ I/O until the controller reconnects.
If it does. If it doesn't, the controller gets removed (so after some 
300 seconds), and MD RAID will get an I/O error, finally.
But then you reconnect the failed path, and you end up with a 
_different_ nvme namespace device.
Requiring you to do manual handholding get the MD RAID into shape again.

With this patch it 'just works' without any interaction.

One might argue if that constitutes a regression (as it's been the 
behaviour since day 1), but it certainly is impaired functionality as 
compared to other drivers/subsystems like SCSI.
And we can't have that, can we?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

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Re: [PATCH 2/2] nvme: delete disk when last path is gone

[Sagi Grimberg]

> The multipath code currently deletes the disk only after all references
> to it are dropped rather than when the last path to that disk is lost.
> This has been reported to cause problems with some use cases like MD RAID.

What is the exact problem?

Can you describe what the problem you see now and what you expect
to see (unrelated to patch #1)?

> This patch implements an alternative behaviour of deleting the disk when
> the last path is gone, ie the same behaviour as non-multipathed nvme
> devices.

But we also don't remove the non-multipath'd nvme device until the
last reference drops (e.g. if you have a mounted filesystem on top).

This would be the equivalent to running raid on top of dm-mpath on
top of scsi devices right? And if all the mpath device nodes go away
the mpath device is deleted even if it has an open reference to it?

> The new behaviour will be selected with the 'fail_if_no_path'
> attribute, as returning it's arguably the same functionality.

But its not the same functionality.

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Re: [PATCH 1/2] nvme: add 'fail_if_no_path' sysfs attribute

[Sagi Grimberg]

On 2/23/21 3:59 AM, Hannes Reinecke wrote:
> In some setups like RAID or cluster we need to return an I/O error
> once all paths are unavailable to allow the upper layers to start
> their own error recovery (like redirecting I/O to other mirrors).
> This patch adds a sysfs attribute 'fail_if_no_path' to allow the
> admin to enable that behaviour instead of the current 'queue until
> a path becomes available' policy.

Doesn't the same happen today if all the controllers are set with
fail_io_fast_tmo=0? nvme_available_path will return false if all
the paths have NVME_CTRL_FAILFAST_EXPIRED set.

I think that fail_io_fast_tmo should be settable via sysfs and I
think I requested that during the various submission iterations...

I'm not sure this should be controlled on the individual namespace level...

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Re: [PATCH 1/2] nvme: add 'fail_if_no_path' sysfs attribute

[Hannes Reinecke]

On 2/24/21 11:47 PM, Sagi Grimberg wrote:
> 
> 
> On 2/23/21 3:59 AM, Hannes Reinecke wrote:
>> In some setups like RAID or cluster we need to return an I/O error
>> once all paths are unavailable to allow the upper layers to start
>> their own error recovery (like redirecting I/O to other mirrors).
>> This patch adds a sysfs attribute 'fail_if_no_path' to allow the
>> admin to enable that behaviour instead of the current 'queue until
>> a path becomes available' policy.
> 
> Doesn't the same happen today if all the controllers are set with
> fail_io_fast_tmo=0? nvme_available_path will return false if all
> the paths have NVME_CTRL_FAILFAST_EXPIRED set.
> 
> I think that fail_io_fast_tmo should be settable via sysfs and I
> think I requested that during the various submission iterations...
> 
> I'm not sure this should be controlled on the individual namespace level...

Indeed, you are right; using 'fast_io_fail_tmo' works as well here.
So I'll be redoing the patch series and will be replacing this patch 
with another one adding a per-controller 'fast_io_fail_tmo' sysfs attribute.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

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Re: [PATCH 2/2] nvme: delete disk when last path is gone

[Hannes Reinecke]

On 2/24/21 11:40 PM, Sagi Grimberg wrote:
> 
>> The multipath code currently deletes the disk only after all references
>> to it are dropped rather than when the last path to that disk is lost.
>> This has been reported to cause problems with some use cases like MD 
>> RAID.
> 
> What is the exact problem?
> 
> Can you describe what the problem you see now and what you expect
> to see (unrelated to patch #1)?
> 
The problem is a difference in behaviour between multipathed and 
non-multipathed namespaces (ie whether 'CMIC' is set or not).
If the CMIC bit is _not_ set, the disk device will be removed once
the controller is gone; if the CMIC bit is set the disk device will be 
retained, and only removed once the last _reference_ is dropped.

This is causing customer issues, as some vendors produce nearly 
identical PCI NVMe devices, which differ in the CMIC bit.
So depending on which device the customer uses, he might be getting on 
or the other behaviour.
And this is causing issues when said customer deploys MD RAID on thems;
with one set of devices PCI hotplug works, with the other set of devices 
it doesn't.

>> This patch implements an alternative behaviour of deleting the disk when
>> the last path is gone, ie the same behaviour as non-multipathed nvme
>> devices.
> 
> But we also don't remove the non-multipath'd nvme device until the
> last reference drops (e.g. if you have a mounted filesystem on top).
> 
Au contraire.

When doing PCI hotplug the controller is removed (in the non-multipathed 
case), and calling 'put_disk()' during nvme_free_ns().
When doing PCI hotplug in the non-multipathed case, the controller is 
removed, too, but put_disk() is only called on the namespace itself; the 
'nshead' disk is still kept around, and put_disk() on the 'nshead' disk 
is only called after the last reference is dropped.

> This would be the equivalent to running raid on top of dm-mpath on
> top of scsi devices right? And if all the mpath device nodes go away
> the mpath device is deleted even if it has an open reference to it?
> 
See above. The prime motivator behind this patch is to get equivalent 
behaviour between multipathed and non-multipathed devices.
It just so happens that MD RAID exercises this particular issue.

>> The new behaviour will be selected with the 'fail_if_no_path'
>> attribute, as returning it's arguably the same functionality.
> 
> But its not the same functionality.

Agreed. But as the first patch will be dropped (see my other mail) I'll 
be redoing the patchset anyway.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

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