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    SubjectRe: [PATCH] vfs: don't hold s_umount over close_bdev_exclusive() call
    On Sat, May 22 2010, Tejun Heo wrote:
    > This patch fixes an obscure AB-BA deadlock in get_sb_bdev().
    > When a superblock is mounted more than once get_sb_bdev() calls
    > close_bdev_exclusive() to drop the extra bdev reference while holding
    > s_umount. However, sb->s_umount nests inside bd_mutex during
    > __invalidate_device() and close_bdev_exclusive() acquires bd_mutex
    > during blkdev_put(); thus creating an AB-BA deadlock.
    > This condition doesn't trigger frequently. For this condition to be
    > visible to lockdep, the filesystem must occupy the whole device (as
    > __invalidate_device() only grabs bd_mutex for the whole device), the
    > FS must be mounted more than once and partition rescan should be
    > issued while the FS is still mounted.
    > Fix it by dropping s_umount over close_bdev_exclusive().

    Looks safe to me, since it has (as you note) an elevated ref count.

    Acked-by: Jens Axboe <>

    Jens Axboe

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      Last update: 2010-05-25 10:33    [W:0.018 / U:1.940 seconds]
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