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

[Mike Snitzer <snitzer@redhat.com>]

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);