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    SubjectRe: hugetlbfs lockdep spew revisited.
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    On Thu, 2012-02-16 at 21:42 -0600, Tyler Hicks wrote:
    > On 2012-02-17 00:49:22, Al Viro wrote:
    > > On Thu, Feb 16, 2012 at 06:38:49PM -0600, Tyler Hicks wrote:
    > > > On 2012-02-16 19:16:34, Josh Boyer wrote:
    > > > > On Thu, Feb 16, 2012 at 07:08:57PM -0500, Dave Jones wrote:
    > > > > > Remember this ? https://lkml.org/lkml/2011/4/15/272
    > > > > > Josh took a stab at fixing it in e096d0c7e2e4e5893792db865dd065ac73cf1f00,
    > > > > > but it seems to still be there.
    > > > >
    > > > > I think Tyler Hicks actually noticed this a while ago, but his patch has
    > > > > been waiting on comment from Al and Christoph:
    > > > >
    > > > > http://thread.gmane.org/gmane.linux.file-systems/58795/focus=59565
    > > > >
    > > > > I've been hesitant to comment because I obviously screwed up once
    > > > > already. We could try this patch in Fedora for a while if Al and
    > > > > company don't speak up soon.
    > > >
    > > > I'm pretty confident that my patch that Josh linked to would "fix" the
    > > > lockdep warning below. According to the backtrace, it is barking about a
    > > > directory inode and a regular inode having a circular locking
    > > > dependency, so deadlock is not possible in this case.
    > >
    > > Sigh... That patch is correct, but it has nothing to do with the locking
    > > order violation that really *is* there. The only benefit would be to
    > > get rid of the "deadlock is not possible" nonsense, since you would see
    > > read/write vs. mmap instead of readdir vs. mmap in the traces. Locking
    > > order is the *same* for directories and nondirectories; both can have
    > > pagefaults under ->i_mutex on their respective inodes. And while mmap
    > > cannot happen for directories, it certainly can happen for regular files,
    > > so taking ->i_mutex in ->mmap() is a plain and simple bug. Should never
    > > be done; in particular, hugetlbfs has ->i_mutex held in read() around
    > > pagefaults, which gives you an obvious deadlock with its ->mmap().
    > >
    > > Folks, this is not a false positive and it has nothing to do with misannotation
    > > for directories. Deadlock is real; I have no idea WTF do we what ->i_mutex
    > > held over that area in hugetlbfs ->mmap(), but doing that is really, really
    > > wrong, whatever the reason.
    >
    > Thanks for clearing that up, Al. I only knew that the inodes were being
    > incorrectly annotated, but I wasn't sure about the correct locking order.
    >
    > Tyler

    Al, thanks for the clarification. An i_mutex/mmap_sem lockdep exists
    for IMA as well. https://lkml.org/lkml/2012/1/24/246 resolves the
    lockdep by moving ima_file_mmap() before the mmap_sem is taken. Do you
    see any problems with this patch?

    thanks,

    Mimi



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