[PATCH] mm: fix refcounting in swapon

[Miklos Szeredi]

From: Miklos Szeredi <mszeredi@xxxxxxx>

Grab a reference to bdev before calling blkdev_get(), which expects
the refcount to be already incremented and either returns success or
decrements the refcount and returns an error.

The bug was introduced by e525fd89 (block: make blkdev_get/put()
handle exclusive access), which didn't take into account this behavior
of blkdev_get().

CC: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
---
 mm/swapfile.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux.git/mm/swapfile.c
===================================================================
--- linux.git.orig/mm/swapfile.c	2011-02-24 15:29:26.000000000 +0100
+++ linux.git/mm/swapfile.c	2011-02-24 15:32:31.000000000 +0100
@@ -1940,7 +1940,7 @@ SYSCALL_DEFINE2(swapon, const char __use
 
 	error = -EINVAL;
 	if (S_ISBLK(inode->i_mode)) {
-		bdev = I_BDEV(inode);
+		bdev = bdgrab(I_BDEV(inode));
 		error = blkdev_get(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL,
 				   sys_swapon);
 		if (error < 0) {
--
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