[PATCH] scsi: zero per-cmd driver data before each I/O

[PATCH] scsi: zero per-cmd driver data before each I/O

[Christoph Hellwig]

Without this drivers that don't clear the state themselves can see off
effects.  For example Hyper-V VMs using the storvsc driver will often
hang during boot due to uncleared Test Unit Ready failures.

Fixes: e9c787e6 ("scsi: allocate scsi_cmnd structures as part of struct request")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Dexuan Cui <decui@microsoft.com>
Tested-by: Dexuan Cui <decui@microsoft.com>
---
 drivers/scsi/scsi_lib.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 90f65c8f487a..daced9db8af8 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1167,6 +1167,7 @@ void scsi_init_command(struct scsi_device *dev, struct scsi_cmnd *cmd)
 	/* zero out the cmd, except for the embedded scsi_request */
 	memset((char *)cmd + sizeof(cmd->req), 0,
 		sizeof(*cmd) - sizeof(cmd->req));
+	memset((char *)(cmd + 1), 0, dev->host->hostt->cmd_size);
 
 	cmd->device = dev;
 	cmd->sense_buffer = buf;
-- 
2.11.0

Re: [PATCH] scsi: zero per-cmd driver data before each I/O

[Bart Van Assche]

On 02/20/2017 08:52 AM, Christoph Hellwig wrote:
> Without this drivers that don't clear the state themselves can see off
> effects.  For example Hyper-V VMs using the storvsc driver will often
> hang during boot due to uncleared Test Unit Ready failures.
> 
> Fixes: e9c787e6 ("scsi: allocate scsi_cmnd structures as part of struct request")
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reported-by: Dexuan Cui <decui@microsoft.com>
> Tested-by: Dexuan Cui <decui@microsoft.com>
> ---
>  drivers/scsi/scsi_lib.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 90f65c8f487a..daced9db8af8 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1167,6 +1167,7 @@ void scsi_init_command(struct scsi_device *dev, struct scsi_cmnd *cmd)
>  	/* zero out the cmd, except for the embedded scsi_request */
>  	memset((char *)cmd + sizeof(cmd->req), 0,
>  		sizeof(*cmd) - sizeof(cmd->req));
> +	memset((char *)(cmd + 1), 0, dev->host->hostt->cmd_size);

Hello Christoph,

Since this code is in the hot path: please combine the two memset()
calls into a single memset() call.

Thanks,

Bart.

Re: [PATCH] scsi: zero per-cmd driver data before each I/O

[Hannes Reinecke]

On 02/20/2017 05:52 PM, Christoph Hellwig wrote:
> Without this drivers that don't clear the state themselves can see off
> effects.  For example Hyper-V VMs using the storvsc driver will often
> hang during boot due to uncleared Test Unit Ready failures.
> 
> Fixes: e9c787e6 ("scsi: allocate scsi_cmnd structures as part of struct request")
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reported-by: Dexuan Cui <decui@microsoft.com>
> Tested-by: Dexuan Cui <decui@microsoft.com>
> ---
>  drivers/scsi/scsi_lib.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 90f65c8f487a..daced9db8af8 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1167,6 +1167,7 @@ void scsi_init_command(struct scsi_device *dev, struct scsi_cmnd *cmd)
>  	/* zero out the cmd, except for the embedded scsi_request */
>  	memset((char *)cmd + sizeof(cmd->req), 0,
>  		sizeof(*cmd) - sizeof(cmd->req));
> +	memset((char *)(cmd + 1), 0, dev->host->hostt->cmd_size);
>  
>  	cmd->device = dev;
>  	cmd->sense_buffer = buf;
> 
Reviewed-by: Hannes Reinecke <hare@suse.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
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