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    SubjectRe: lockdep warning for iscsi in 2.6.33-rc6
    On 02/09/2010 06:42 PM, Tao Ma wrote:
    > Hi Mike,
    > Mike Christie wrote:
    >> On 02/09/2010 12:59 AM, Tao Ma wrote:
    >>> Hi Mike,
    >>> I meet with a lockdep warning for iscsi in 2.6.33-rc6.
    >>> the lockdep is attached.
    >> If the lockdep output is saying that there is a problem with the iscsi
    >> host taking its mutex then the scsi host mutex, I think that might be
    >> a mistake in the lockdep detection. We always take the iscsi host
    >> mutex then take the scsi host mutex.
    >> Could it get confused if we are scanning two hosts at the same time?
    >> If it is just looking at if a lock is being taken then it would look
    >> like host1 has its ihost->mutex and then took its shost->mutex, but
    >> then host2 could start to get scanned at the same time, and it is
    >> going to take its ihost->mutex. It would then look like we are trying
    >> to grab a ihost->mutex while holding a shost->mutex. However, the
    >> mutexs are not global and they are different instances of the mutex
    >> because each host has its own.
    > If these 2 mutexes are grabed in the same order(in your description,
    > ihost->mutex first and then shost->mutex), there would be no problem.

    I checked the code and we are taking the locks in the proper order, but
    I did some more testing and I do not think it was detecting what I
    thought above.

    I just did a login with one iscsi session and got the lockdep warning.
    So I will do some more digging into what is going on.

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      Last update: 2010-02-12 18:23    [W:0.022 / U:27.348 seconds]
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