linux-kernel - [PATCH 4.2.y-ckt 200/305] Revert "SCSI: Fix NULL pointer dereference in runtime PM"

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Message-Id: <1452902519-2754-201-git-send-email-kamal@canonical.com>
Date:	Fri, 15 Jan 2016 16:00:14 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Ken Xue <Ken.Xue@....com>, Xiangliang Yu <Xiangliang.Yu@....com>,
	"James E.J. Bottomley" <JBottomley@...n.com>,
	Jens Axboe <axboe@...nel.dk>,
	Michael Terry <Michael.terry@...onical.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 200/305] Revert "SCSI: Fix NULL pointer dereference in runtime PM"

4.2.8-ckt2 -stable review patch.  If anyone has any objections, please let me know.

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

From: Ken Xue <ken.xue@....com>

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@....com>
Acked-by: Alan Stern <stern@...land.harvard.edu>
Cc: Xiangliang Yu <Xiangliang.Yu@....com>
Cc: James E.J. Bottomley <JBottomley@...n.com>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: Michael Terry <Michael.terry@...onical.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.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 e4b7998..459abe1 100644
--- a/drivers/scsi/scsi_pm.c
+++ b/drivers/scsi/scsi_pm.c
@@ -219,13 +219,13 @@ 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;
 }
 
@@ -248,11 +248,11 @@ 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;
 }
 
-- 
1.9.1