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    SubjectRe: [Patch 0/2] sysfs: fix s_active lockdep warning
    Dave Young wrote:
    > On Mon, Feb 8, 2010 at 11:08 AM, Cong Wang <amwang@redhat.com> wrote:
    >> Dave Young wrote:
    >>> On Fri, Feb 05, 2010 at 04:41:57PM +0100, Peter Zijlstra wrote:
    >>>> On Fri, 2010-02-05 at 10:30 -0500, Alan Stern wrote:
    >>>>> On Fri, 5 Feb 2010, Peter Zijlstra wrote:
    >>>>>
    >>>>>> Right, so this device stuff is much more complicated than I was led to
    >>>>>> believe ;-)
    >>>>> Haven't I told you all along that tree-structured locking is
    >>>>> complicated? :-)
    >>>> Well, regular tree's aren't all that complicated, but multiple
    >>>> inter-locking trees is a whole different story indeed.
    >>>>
    >>> I ever tried converting device semaphore to mutex, but failed with same
    >>> issue.
    >>>
    >>> At least now there's no lockdep solution for it, so I recommend revert
    >>> the mutex converting patch.
    >>>
    >>> following lockdep warning with rc6-mm1:
    >>>
    >>> [ 0.397123] [ 0.397124]
    >>> =============================================
    >>> [ 0.397359] [ INFO: possible recursive locking detected ]
    >>> [ 0.397480] 2.6.33-rc6-mm1 #1
    >>> [ 0.397596] ---------------------------------------------
    >>> [ 0.397717] swapper/1 is trying to acquire lock:
    >>> [ 0.397836] (&dev->mutex){+.+...}, at: [<c12662e4>]
    >>> __driver_attach+0x38/0x63
    >>> [ 0.398162] [ 0.398162] but task is already holding lock:
    >>> [ 0.398393] (&dev->mutex){+.+...}, at: [<c12662d8>]
    >>> __driver_attach+0x2c/0x63
    >>> [ 0.399999]
    >> Alan already provided a patch for this issue earlier in this thread.
    >
    > Yes, but device locks can not be classified with regular tree style.

    True, Alan mentioned the device trees could be more than one,
    which is the difference with the sysfs, I think, where we only
    have one tree.

    > Please read the whole thread.

    Surely I did.



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