• Peter Zijlstra's avatar
    [PATCH] lockdep: fix blkdev_open() warning · 6946bd63
    Peter Zijlstra authored
    On Wed, 2006-08-09 at 07:57 +0200, Rolf Eike Beer wrote:
    > =============================================
    > [ INFO: possible recursive locking detected ]
    > ---------------------------------------------
    > parted/7929 is trying to acquire lock:
    >  (&bdev->bd_mutex){--..}, at: [<c105eb8d>] __blkdev_put+0x1e/0x13c
    > but task is already holding lock:
    >  (&bdev->bd_mutex){--..}, at: [<c105eec6>] do_open+0x72/0x3a8
    > other info that might help us debug this:
    > 1 lock held by parted/7929:
    >  #0:  (&bdev->bd_mutex){--..}, at: [<c105eec6>] do_open+0x72/0x3a8
    > stack backtrace:
    >  [<c1003aad>] show_trace_log_lvl+0x58/0x15b
    >  [<c100495f>] show_trace+0xd/0x10
    >  [<c1004979>] dump_stack+0x17/0x1a
    >  [<c102dee5>] __lock_acquire+0x753/0x99c
    >  [<c102e3b0>] lock_acquire+0x4a/0x6a
    >  [<c1204501>] mutex_lock_nested+0xc8/0x20c
    >  [<c105eb8d>] __blkdev_put+0x1e/0x13c
    >  [<c105ecc4>] blkdev_put+0xa/0xc
    >  [<c105f18a>] do_open+0x336/0x3a8
    >  [<c105f21b>] blkdev_open+0x1f/0x4c
    >  [<c1057b40>] __dentry_open+0xc7/0x1aa
    >  [<c1057c91>] nameidata_to_filp+0x1c/0x2e
    >  [<c1057cd1>] do_filp_open+0x2e/0x35
    >  [<c1057dd7>] do_sys_open+0x38/0x68
    >  [<c1057e33>] sys_open+0x16/0x18
    >  [<c1002845>] sysenter_past_esp+0x56/0x8d
    OK, I'm having a look here; its all new to me so bear with me.
    blkdev_open() calls
      do_open(bdev, ...,BD_MUTEX_NORMAL) and takes
        mutex_lock_nested(&bdev->bd_mutex, BD_MUTEX_NORMAL)
    then something fails, and we're thrown to:
    out_first: where
        if (bdev != bdev->bd_contains)
          blkdev_put(bdev->bd_contains) which is
            __blkdev_put(bdev->bd_contains, BD_MUTEX_NORMAL) which does
              mutex_lock_nested(&bdev->bd_contains->bd_mutex, BD_MUTEX_NORMAL) <--- lockdep trigger
    When going to out_first, dbev->bd_contains is either bdev or whole, and
    since we take the branch it must be whole. So it seems to me the
    following patch would be the right one:
    [akpm@osdl.org: compile fix]
    Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Arjan van de Ven <arjan@linux.intel.com>
    Acked-by: default avatarNeilBrown <neilb@suse.de>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
block_dev.c 31.3 KB