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    SubjectRe: INFO: possible circular locking dependency detected 3.1.0-rc2-00190-g3210d19
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    On Mon, Aug 22, 2011 at 9:27 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
    > On Mon, Aug 22, 2011 at 02:16:21PM +0100, Al Viro wrote:
    >> On Mon, Aug 22, 2011 at 09:09:14AM -0400, Josh Boyer wrote:
    >>
    >> > We've had a report of this on 3.0.1 as well.  Slightly different
    >> > scenario and fs, but the locks in question are the same.
    >> > https://bugzilla.redhat.com/show_bug.cgi?id=730998
    >> >
    >> > It seems that with CONFIG_PROVE_LOCKING on, might_fault will always
    >> > attempt to grab mm->mmap_sem.  The common flow here is that getdents
    >> > calls filldir, which calls copy_to_user, which is what is calling
    >> > might_fault.
    >> >
    >> > Beyond that, I'm a bit over my head at the moment because I don't know
    >> > if the VFS is right and we just need some more lockdep annotations or
    >> > if there really is a problem.
    >>
    >> Don't grab ->i_mutex in ->evict_inode().  Why are you doing that, anyway?
    >
    > Note, BTW, that readdir() is a red herring here; there is a much more
    > relevant reason for that ranking.  Namely, write() doing copy_from_user()
    > when the file we are writing into has i_mutex held by us.  That can fault
    > and in this case we have a non-directory inode.  While you can't have
    > directory mmapped, regular files can be mmapped just fine.

    So the lockdep report in the RHBZ (which now that I look at it
    probably isn't the same as this report) seems to be doing a readdir
    while find is trying to mmap, which is calling into
    hugetlbfs_file_mmap and throwing the same deadlock warning. Is that
    like the scenario you are describing above?

    josh
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