Re: [PATCH] gdth: Use scsi_get_command for gdth internal commands

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Wed, 2008-03-19 at 11:57 +0200, Boaz Harrosh wrote:
> On Tue, Mar 18 2008 at 20:54 +0200, James Bottomley <James.Bottomley@HansenPartnership.com> wrote:
> > On Tue, 2008-03-18 at 20:18 +0200, Boaz Harrosh wrote:
> >> This is for for the next kernel window (v2.6.26). It is based on top of
> >> both scsi-misc and scsi-rc-fixes. Once scsi-misc rebases to scsi-rc-fixes
> >> this patch can be committed.
> >>
> >> Boaz
> >> ---
> >> From: Boaz Harrosh <bharrosh@panasas.com>
> >> Date: Tue, 11 Mar 2008 17:42:06 +0200
> >> Subject: [PATCH] gdth: Use scsi_get_command for gdth internal commands
> >>
> >> use scsi_get_command() in __gdth_execute() of internal commands for two reasons.
> >> - To be insulated from future scsi-ml changes and the way scsi_cmnd is
> >>   structured / allocated.
> >> - Hold onto the scsi_device while executing since execution can come from
> >>   user-mode management SW through the gdth char device.
> >>
> >> Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
> >> Tested-by: Sven Schnelle <svens@bitebene.org>
> >> ---
> >>  drivers/scsi/gdth.c |   12 ++----------
> >>  1 files changed, 2 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/drivers/scsi/gdth.c b/drivers/scsi/gdth.c
> >> index c6d6e7c..c6e2b8d 100644
> >> --- a/drivers/scsi/gdth.c
> >> +++ b/drivers/scsi/gdth.c
> >> @@ -448,17 +448,10 @@ int __gdth_execute(struct scsi_device *sdev, gdth_cmd_str *gdtcmd, char *cmnd,
> >>      DECLARE_COMPLETION_ONSTACK(wait);
> >>      int rval;
> >>  
> >> -    scp = kzalloc(sizeof(*scp), GFP_KERNEL);
> >> +    scp = scsi_get_command(sdev, GFP_KERNEL);
> >>      if (!scp)
> >>          return -ENOMEM;
> >>  
> >> -    scp->sense_buffer = kzalloc(SCSI_SENSE_BUFFERSIZE, GFP_KERNEL);
> >> -    if (!scp->sense_buffer) {
> >> -	kfree(scp);
> >> -	return -ENOMEM;
> >> -    }
> >> -
> >> -    scp->device = sdev;
> >>      memset(&cmndinfo, 0, sizeof(cmndinfo));
> >>  
> >>      /* use request field to save the ptr. to completion struct. */
> >> @@ -478,8 +471,7 @@ int __gdth_execute(struct scsi_device *sdev, gdth_cmd_str *gdtcmd, char *cmnd,
> >>      rval = cmndinfo.status;
> >>      if (info)
> >>          *info = cmndinfo.info;
> >> -    kfree(scp->sense_buffer);
> >> -    kfree(scp);
> >> +    scsi_put_command(scp);
> >>      return rval;
> > 
> > This needs to be the scsi_allocate_command/scsi_free_command interface.  Other than that, it looks fine.
> > 
> > James
> > 
> > 
> 
> No, I disagree, and I said that in the commit log above. 

You can't use scsi_get_command() because it will violate the forward
progress guarantees that the writeout deadlock avoidance relies on.

> I like how we take the reference to the device by doing it through the
> scsi_device.

It's executing on the host device.  The whole difference between the
gdth_execute() and __gdth_execute() paths is whether you need a
reference to the host device, so another reference is redundant.

>  __gdth_execute in
> principle should have been using simple scsi_execute(). It does not because it
> sends none_standard commands that would choke the midlayer. Actually once my
> varlen patches go through we could easily convert it.
> 
> (In the USB case you are right)

James