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block: fix refcounting in BLKBSZSET

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Adam Kovari and others reported that disconnecting an USB drive with
an ntfs-3g filesystem would cause "kernel BUG at fs/inode.c:1421!" to
be triggered.

The BUG could be traced back to ioctl(BLKBSZSET), which would
erroneously decrement the refcount on the bdev.  This is because
blkdev_get() 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().

This fixes
  https://bugzilla.kernel.org/show_bug.cgi?id=29202
(and likely 29792 too)

Reported-by: Adam Kovari <kovariadam@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Miklos Szeredi 2011-02-24 15:45:41 +01:00 committed by Linus Torvalds
parent dcace5ac85
commit 3c522cedb5
1 changed files with 5 additions and 3 deletions
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8
block/ioctl.c
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@ -294,9 +294,11 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
return -EINVAL;
if (get_user(n, (int __user *) arg))
return -EFAULT;
if (!(mode & FMODE_EXCL) &&
blkdev_get(bdev, mode | FMODE_EXCL, &bdev) < 0)
return -EBUSY;
if (!(mode & FMODE_EXCL)) {
bdgrab(bdev);
if (blkdev_get(bdev, mode | FMODE_EXCL, &bdev) < 0)
return -EBUSY;
}
ret = set_blocksize(bdev, n);
if (!(mode & FMODE_EXCL))
blkdev_put(bdev, mode | FMODE_EXCL);