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    SubjectRe: [PATCH 01/12] Use mutex instead of semaphore in driver core
    On Dec 30, 2007 6:01 AM, Alan Stern <stern@rowland.harvard.edu> wrote:
    >
    > On Sat, 29 Dec 2007, Dave Young wrote:
    >
    > > On Dec 29, 2007 1:06 PM, Dave Young <hidave.darkstar@gmail.com> wrote:
    > > >
    > > > On Dec 29, 2007 12:42 PM, Greg KH <gregkh@suse.de> wrote:
    > > > > On Sat, Dec 29, 2007 at 10:36:49AM +0800, Dave Young wrote:
    > > > > > >
    > > > > > The full boot dmesg with lockdep output is out, there's one warnings in it :
    > > > >
    > > > > Please fix that warning before the next repost of these patches (along
    > > > > with fixing the problem of them not being able to be applied and
    > > > > successfully built at every point in the series...)
    > > > >
    > > >
    > > > Ok, thanks, I will fix them and repost.
    > > >
    > >
    > > Hi,
    > > After digging the code, I feel hard to fix the lockdep warning due to
    > > some misterious relationship with usb.
    > >
    > > Could someone help on this? thanks.
    > > Add usb-devel list as cc
    >
    > The problem isn't specific to USB. And you will not be able to fix it
    > unless you make drastic changes to the lockdep checker.
    >
    > lockdep warns whenever a task acquires a mutex while holding another
    > mutex of the same kind (that is, the same member in another structure
    > of the same type). But there are lots of places where the kernel needs
    > to acquire dev->sem for one device while already holding
    > dev->parent->sem. There's no way to remove these, which means there's
    > no way to prevent lockdep from issuing a warning.
    >
    > Around a month ago I had a discussion with Peter Zijlstra about the
    > problems in converting the device semaphores to mutexes; you may be
    > able to find it in the LKML archives. Doing the conversion while
    > keeping lockdep happy is a very hard problem and we were not able to
    > solve it.
    >

    It's unfortunate to know this, I will search and read your thread.

    > It's possible that you may be able to convert the semaphores in struct
    > class or other structures. But you won't succeed with struct device.
    >
    > Alan Stern
    >
    >


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