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

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Date:   Tue, 13 Jun 2017 15:38:06 +0000
From:   Bart Van Assche <Bart.VanAssche@...disk.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kys@...rosoft.com" <kys@...rosoft.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "sthemmin@...rosoft.com" <sthemmin@...rosoft.com>,
        "longli@...hange.microsoft.com" <longli@...hange.microsoft.com>,
        "jejb@...ux.vnet.ibm.com" <jejb@...ux.vnet.ibm.com>,
        "haiyangz@...rosoft.com" <haiyangz@...rosoft.com>
CC:     "jthumshirn@...e.de" <jthumshirn@...e.de>,
        "longli@...rosoft.com" <longli@...rosoft.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@...rosoft.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@...rosoft.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.