[3.16.y-ckt stable] Patch "Revert "SCSI: Fix NULL pointer dereference in runtime PM"" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    Revert "SCSI: Fix NULL pointer dereference in runtime PM"

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt23.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

---8<------------------------------------------------------------

>From 82ec0ff92a07112f82f1647ea7d97c6d996ee67b Mon Sep 17 00:00:00 2001
From: Ken Xue <ken.xue at amd.com>
Date: Tue, 1 Dec 2015 14:45:23 +0800
Subject: Revert "SCSI: Fix NULL pointer dereference in runtime PM"

commit 1c69d3b6eb73e466ecbb8edaf1bc7fd585b288da upstream.

This reverts commit 49718f0fb8c9 ("SCSI: Fix NULL pointer dereference in
runtime PM")

The old commit may lead to a issue that blk_{pre|post}_runtime_suspend and
blk_{pre|post}_runtime_resume may not be called in pairs.

Take sr device as example, when sr device goes to runtime suspend,
blk_{pre|post}_runtime_suspend will be called since sr device defined
pm->runtime_suspend. But blk_{pre|post}_runtime_resume will not be called
since sr device doesn't have pm->runtime_resume. so, sr device can not
resume correctly anymore.

More discussion can be found from below link.
http://marc.info/?l=linux-scsi&m=144163730531875&w=2

Signed-off-by: Ken Xue <Ken.Xue at amd.com>
Acked-by: Alan Stern <stern at rowland.harvard.edu>
Cc: Xiangliang Yu <Xiangliang.Yu at amd.com>
Cc: James E.J. Bottomley <JBottomley at odin.com>
Cc: Jens Axboe <axboe at kernel.dk>
Cc: Michael Terry <Michael.terry at canonical.com>
Signed-off-by: Martin K. Petersen <martin.petersen at oracle.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/scsi/scsi_pm.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c
index a2dcf6a54ec6..75320dad9677 100644
--- a/drivers/scsi/scsi_pm.c
+++ b/drivers/scsi/scsi_pm.c
@@ -221,13 +221,13 @@ static int sdev_runtime_suspend(struct device *dev)
 	struct scsi_device *sdev = to_scsi_device(dev);
 	int err = 0;

-	if (pm && pm->runtime_suspend) {
-		err = blk_pre_runtime_suspend(sdev->request_queue);
-		if (err)
-			return err;
+	err = blk_pre_runtime_suspend(sdev->request_queue);
+	if (err)
+		return err;
+	if (pm && pm->runtime_suspend)
 		err = pm->runtime_suspend(dev);
-		blk_post_runtime_suspend(sdev->request_queue, err);
-	}
+	blk_post_runtime_suspend(sdev->request_queue, err);
+
 	return err;
 }

@@ -250,11 +250,11 @@ static int sdev_runtime_resume(struct device *dev)
 	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
 	int err = 0;

-	if (pm && pm->runtime_resume) {
-		blk_pre_runtime_resume(sdev->request_queue);
+	blk_pre_runtime_resume(sdev->request_queue);
+	if (pm && pm->runtime_resume)
 		err = pm->runtime_resume(dev);
-		blk_post_runtime_resume(sdev->request_queue, err);
-	}
+	blk_post_runtime_resume(sdev->request_queue, err);
+
 	return err;
 }