[PATCH] storvsc: use default I/O timeout handler for FC devices

[PATCH] storvsc: use default I/O timeout handler for FC devices

[Long Li]

From: Long Li <longli@microsoft.com>

FC disks are usually setup in a multipath system, and they don't want to 
unconditionaly reset I/O on timeout. I/O timeout is detected by multipath 
as a good time to failover and recover.

Signed-off-by: Long Li <longli@microsoft.com>
---
 drivers/scsi/storvsc_drv.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 8d955db..d60b5ea 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -486,6 +486,7 @@ struct hv_host_device {
 	unsigned int port;
 	unsigned char path;
 	unsigned char target;
+	bool is_fc;
 };
 
 struct storvsc_scan_work {
@@ -1495,6 +1496,11 @@ static int storvsc_host_reset_handler(struct scsi_cmnd *scmnd)
  */
 static enum blk_eh_timer_return storvsc_eh_timed_out(struct scsi_cmnd *scmnd)
 {
+	struct hv_host_device *host_dev = shost_priv(scmnd->device->host);
+
+	if (host_dev->is_fc)
+		return BLK_EH_NOT_HANDLED;
+
 	return BLK_EH_RESET_TIMER;
 }
 
@@ -1738,6 +1744,7 @@ static int storvsc_probe(struct hv_device *device,
 
 	host_dev->port = host->host_no;
 	host_dev->dev = device;
+	host_dev->is_fc = is_fc;
 
 
 	stor_device = kzalloc(sizeof(struct storvsc_device), GFP_KERNEL);
-- 
2.7.4

Re: [PATCH] storvsc: use default I/O timeout handler for FC devices

[Johannes Thumshirn]

On 06/13/2017 02:23 AM, Long Li wrote:
> From: Long Li <longli@microsoft.com>
> 
> FC disks are usually setup in a multipath system, and they don't want to 
> unconditionaly reset I/O on timeout. I/O timeout is detected by multipath 
> as a good time to failover and recover.
> 
> Signed-off-by: Long Li <longli@microsoft.com>
> ---

Looks good,
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>

-- 
Johannes Thumshirn                                          Storage
jthumshirn@suse.de                                +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Jane Smithard, Graham Norton
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Key fingerprint = EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850

Re: [Possible Phish Fraud][PATCH] storvsc: use default I/O timeout handler for FC devices

[Bart Van Assche]

On Mon, 2017-06-12 at 17:23 -0700, Long Li wrote:
> From: Long Li <longli@microsoft.com>
> 
> FC disks are usually setup in a multipath system, and they don't want to 
> unconditionaly reset I/O on timeout. I/O timeout is detected by multipath 
> as a good time to failover and recover.
> 
> Signed-off-by: Long Li <longli@microsoft.com>
> ---
>  drivers/scsi/storvsc_drv.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
> index 8d955db..d60b5ea 100644
> --- a/drivers/scsi/storvsc_drv.c
> +++ b/drivers/scsi/storvsc_drv.c
> @@ -486,6 +486,7 @@ struct hv_host_device {
>  	unsigned int port;
>  	unsigned char path;
>  	unsigned char target;
> +	bool is_fc;
>  };
>  
>  struct storvsc_scan_work {
> @@ -1495,6 +1496,11 @@ static int storvsc_host_reset_handler(struct scsi_cmnd *scmnd)
>   */
>  static enum blk_eh_timer_return storvsc_eh_timed_out(struct scsi_cmnd *scmnd)
>  {
> +	struct hv_host_device *host_dev = shost_priv(scmnd->device->host);
> +
> +	if (host_dev->is_fc)
> +		return BLK_EH_NOT_HANDLED;
> +
>  	return BLK_EH_RESET_TIMER;
>  }
>  
> @@ -1738,6 +1744,7 @@ static int storvsc_probe(struct hv_device *device,
>  
>  	host_dev->port = host->host_no;
>  	host_dev->dev = device;
> +	host_dev->is_fc = is_fc;
>  
>  
>  	stor_device = kzalloc(sizeof(struct storvsc_device), GFP_KERNEL);

Hello Long,

As far as I know there is no other SCSI driver nor block driver in the Linux
kernel tree that returns BLK_EH_RESET_TIMER unconditionally. Would a valid
alternative fix be to remove storvsc_eh_timed_out() entirely? If not, what
would break if that function would be removed entirely?

Additionally, for FC, shouldn't that timeout handler handle the "port blocked"
state? Shouldn't fc_eh_timed_out() be used for FC instead of just returning
BLK_EH_NOT_HANDLED?

Thanks,

Bart.

RE: [Possible Phish Fraud][PATCH] storvsc: use default I/O timeout handler for FC devices

[Long Li]

> -----Original Message-----
> From: Bart Van Assche [mailto:Bart.VanAssche@sandisk.com]
> Sent: Tuesday, June 13, 2017 8:38 AM
> To: linux-kernel@vger.kernel.org; KY Srinivasan <kys@microsoft.com>;
> martin.petersen@oracle.com; linux-scsi@vger.kernel.org; Stephen Hemminger
> <sthemmin@microsoft.com>; Long Li <longli@microsoft.com>;
> jejb@linux.vnet.ibm.com; Haiyang Zhang <haiyangz@microsoft.com>
> Cc: jthumshirn@suse.de; Long Li <longli@microsoft.com>
> Subject: Re: [Possible Phish Fraud][PATCH] storvsc: use default I/O timeout
> handler for FC devices
> 
> On Mon, 2017-06-12 at 17:23 -0700, Long Li wrote:
> > From: Long Li <longli@microsoft.com>
> >
> > FC disks are usually setup in a multipath system, and they don't want
> > to unconditionaly reset I/O on timeout. I/O timeout is detected by
> > multipath as a good time to failover and recover.
> >
> > Signed-off-by: Long Li <longli@microsoft.com>
> > ---
> >  drivers/scsi/storvsc_drv.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
> > index 8d955db..d60b5ea 100644
> > --- a/drivers/scsi/storvsc_drv.c
> > +++ b/drivers/scsi/storvsc_drv.c
> > @@ -486,6 +486,7 @@ struct hv_host_device {
> >  	unsigned int port;
> >  	unsigned char path;
> >  	unsigned char target;
> > +	bool is_fc;
> >  };
> >
> >  struct storvsc_scan_work {
> > @@ -1495,6 +1496,11 @@ static int storvsc_host_reset_handler(struct
> scsi_cmnd *scmnd)
> >   */
> >  static enum blk_eh_timer_return storvsc_eh_timed_out(struct scsi_cmnd
> > *scmnd)  {
> > +	struct hv_host_device *host_dev = shost_priv(scmnd->device->host);
> > +
> > +	if (host_dev->is_fc)
> > +		return BLK_EH_NOT_HANDLED;
> > +
> >  	return BLK_EH_RESET_TIMER;
> >  }
> >
> > @@ -1738,6 +1744,7 @@ static int storvsc_probe(struct hv_device
> > *device,
> >
> >  	host_dev->port = host->host_no;
> >  	host_dev->dev = device;
> > +	host_dev->is_fc = is_fc;
> >
> >
> >  	stor_device = kzalloc(sizeof(struct storvsc_device), GFP_KERNEL);
> 
> Hello Long,
> 
> As far as I know there is no other SCSI driver nor block driver in the Linux kernel
> tree that returns BLK_EH_RESET_TIMER unconditionally. Would a valid
> alternative fix be to remove storvsc_eh_timed_out() entirely? If not, what
> would break if that function would be removed entirely?

Storvsc handles virtualized devices for Hyper-V and Azure. The host decides on how to handle I/O timeout, and makes decision based on how long I/O has been in flight. This is why we use BLK_EH_RESET_TIMER and leave the I/O timeout handling to the host for most cases.

> 
> Additionally, for FC, shouldn't that timeout handler handle the "port blocked"
> state? Shouldn't fc_eh_timed_out() be used for FC instead of just returning
> BLK_EH_NOT_HANDLED?

I agree with you. Storvsc didn't expose rport state. But this has changed with a recent commit daf0cd445a218314f9461d67d4f2b9c24cdd534b. I'll send a V2 to address this.

Thank you

Long

> 
> Thanks,
> 
> Bart.