Re: [PATCH for-2.6.39] [SCSI] scsi_dh_emc: fix panic when handling multiple path failures

[Eddie Williams <Eddie.Williams@us.sios.com>]

oops, blasted google mail converted it to html...

On Mon, Mar 21, 2011 at 10:33 PM, Eddie Williams
<Eddie.Williams@us.sios.com> wrote:
>
> OK, I will give it a test in the morning...
> Eddie
>
> On Mon, Mar 21, 2011 at 7:16 PM, Mike Snitzer <snitzer@redhat.com> wrote:
>>
>> On Mon, Mar 21 2011 at  4:44pm -0400,
>> James Bottomley <James.Bottomley@suse.de> wrote:
>>
>> > On Mon, 2011-03-21 at 16:38 -0400, Mike Snitzer wrote:
>> > > Anyway, it's now on my plate to sort out.  No idea if I'll do so by the
>> > > close of the merge window.  But maybe a real fix to this can go in after
>> > > the window closes?
>> >
>> > It's a bug fix: of course it can.
>>
>> Right, so given scsi_dh_activate()'s {get,put}_device() that wraps the
>> call to scsi_dh->activate (aka clariion_activate) I'm not seeing how
>> accessing sdev->sdev_gendev (via sdev_printk) could result in a panic.
>> So I'll need to dig deeper (hopefully with Eddie's assistance)...
>>
>> But now that I look it at scsi_dh_activate's 'err' path, it would appear
>> that we don't drop the reference (put_device) before returning 'err'.  I
>> unfotunately had a role in the offending change (commit: db422318)
>> getting upstream.  /me ducks
>>
>> Looks to me like we need this:
>>
>>
>> From: Mike Snitzer <snitzer@redhat.com>
>> Subject: [SCSI] scsi_dh: fix reference counting in scsi_dh_activate error path
>>
>> Commit db422318cbca55168cf965f655471dbf8be82433 ([SCSI] scsi_dh:
>> propagate SCSI device deletion) introduced a regression where the device
>> reference is not dropped prior to scsi_dh_activate's early return from
>> the error path.
>>
>> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
>> Cc: stable@kernel.org
>> ---
>>  drivers/scsi/device_handler/scsi_dh.c |    9 ++++++---
>>  1 files changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/scsi/device_handler/scsi_dh.c b/drivers/scsi/device_handler/scsi_dh.c
>> index 564e6ec..0119b81 100644
>> --- a/drivers/scsi/device_handler/scsi_dh.c
>> +++ b/drivers/scsi/device_handler/scsi_dh.c
>> @@ -394,12 +394,14 @@ int scsi_dh_activate(struct request_queue *q, activate_complete fn, void *data)
>>        unsigned long flags;
>>        struct scsi_device *sdev;
>>        struct scsi_device_handler *scsi_dh = NULL;
>> +       struct device *dev = NULL;
>>
>>        spin_lock_irqsave(q->queue_lock, flags);
>>        sdev = q->queuedata;
>>        if (sdev && sdev->scsi_dh_data)
>>                scsi_dh = sdev->scsi_dh_data->scsi_dh;
>> -       if (!scsi_dh || !get_device(&sdev->sdev_gendev) ||
>> +       dev = get_device(&sdev->sdev_gendev);
>> +       if (!scsi_dh || !dev ||
>>            sdev->sdev_state == SDEV_CANCEL ||
>>            sdev->sdev_state == SDEV_DEL)
>>                err = SCSI_DH_NOSYS;
>> @@ -410,12 +412,13 @@ int scsi_dh_activate(struct request_queue *q, activate_complete fn, void *data)
>>        if (err) {
>>                if (fn)
>>                        fn(data, err);
>> -               return err;
>> +               goto out;
>>        }
>>
>>        if (scsi_dh->activate)
>>                err = scsi_dh->activate(sdev, fn, data);
>> -       put_device(&sdev->sdev_gendev);
>> +out:
>> +       put_device(dev);
>>        return err;
>>  }
>>  EXPORT_SYMBOL_GPL(scsi_dh_activate);
>>
>
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