linux-kernel - Re: blkdev_get() change causes OOPS...

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Date:	Wed, 1 Jun 2011 00:37:44 +0900
From:	Tejun Heo <tj@...nel.org>
To:	David Miller <davem@...emloft.net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: blkdev_get() change causes OOPS...

On Mon, May 30, 2011 at 10:35:07PM -0700, David Miller wrote:
> 
> I don't think whole->bd_disk is guaranteed to be non-NULL where you're
> dereferencing it in blkdev_get() after commit
> d4dc210f69bcb0b4bef5a83b1c323817be89bad1 ("block: don't block events
> on excl write for non-optical devices")

Ah... right, it's there if open succeeded.  I should have put the test
after !res test.  Does the following patch fix the problem?

Thanks.

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 1f2b199..1a2421f 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1272,8 +1272,8 @@ int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
 		 * individual writeable reference is too fragile given the
 		 * way @mode is used in blkdev_get/put().
 		 */
-		if ((disk->flags & GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE) &&
-		    !res && (mode & FMODE_WRITE) && !bdev->bd_write_holder) {
+		if (!res && (mode & FMODE_WRITE) && !bdev->bd_write_holder &&
+		    (disk->flags & GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE)) {
 			bdev->bd_write_holder = true;
 			disk_block_events(disk);
 		}

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