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    SubjectRe: 3.1.0-rc3 -- INFO: possible circular locking dependency detected
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    On Tue, Aug 23, 2011 at 9:04 AM, Dave Chinner <david@fromorbit.com> wrote:
    > On Tue, Aug 23, 2011 at 07:59:20AM -0400, Josh Boyer wrote:
    >> On Tue, Aug 23, 2011 at 7:49 AM, Dave Chinner <david@fromorbit.com> wrote:
    >> >> >  Possible unsafe locking scenario:
    >> >> >
    >> >> >       CPU0                    CPU1
    >> >> >       ----                    ----
    >> >> >  lock(&mm->mmap_sem);
    >> >> >                               lock(&sb->s_type->i_mutex_key);
    >> >> >                               lock(&mm->mmap_sem);
    >> >> >  lock(&sb->s_type->i_mutex_key);
    >> >> >
    >> >> >  *** DEADLOCK ***
    >> >>
    >> >> This one was reported yesterday: https://lkml.org/lkml/2011/8/21/163
    >> >> and we're hoping Ted (or someone else from the ext4 camp) can comment
    >> >> on why ext4_evict_inode is holding i_mutex.
    >> >
    >> > Actually, the problem has nothing to do with ext4. the problem is
    >> > that remove_vma() is holding the mmap_sem while calling fput(). The
    >> > correct locking order is i_mutex->mmap_sem, as documented in
    >> > mm/filemap.c:
    >> >
    >> >  *  ->i_mutex                   (generic_file_buffered_write)
    >> >  *    ->mmap_sem                (fault_in_pages_readable->do_page_fault)
    >> >
    >> >
    >> > The way remove_vma() calls fput() also triggers lockdep reports in
    >> > XFS and it will do so with any filesystem that takes an inode
    >> > specific lock in it's evict() processing. IOWs, remove_vma() needs
    >> > fixing, not ext4....
    >>
    >> Er... ok.  So the remove_vma code hasn't changed since 2008.  We're
    >> only seeing this issue now because the debugging code has improved,
    >> or?
    >
    > The problem has been there since at least 2008.  Here's an early
    > XFS report from 2.6.24:
    >
    > http://oss.sgi.com/archives/xfs/2008-02/msg00931.html
    >
    > Here's an XFS report
    > to match the ext4 one in this thread from 2009:
    >
    > http://oss.sgi.com/archives/xfs/2009-03/msg00149.html
    >
    > You won't find reports much older than this - it only started to be
    > reported when lockdep support in XFS matured and it started to be
    > widely used....
    >
    >> At any rate, the proposed solution is to make remove_vma drop mmap_sem
    >> before calling fput, or make it not call fput, or?
    >
    > Ask the VM folk - this is the only response I can remember from them
    > is this:
    >
    > http://oss.sgi.com/archives/xfs/2009-03/msg00224.html
    >
    > Maybe now that ext4 is hitting the problem something will be done
    > about it...

    OK. I've CC'd Andrew and Hugh, so maybe we can get a discussion going.

    josh
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