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    SubjectRe: [PATCH] hugetlbfs: lockdep annotate root inode properly
    On Thu, Mar 08, 2012 at 01:40:50PM -0800, Andrew Morton wrote:

    > OK, thanks, yup. Taking i_mutex in file_operations.mmap() is wrong.

    ... or in .release() (munmap() does fput() under mmap_sem).

    > Is hugetlbfs actually deadlockable because of this, or is it the case
    > that the i_mutex->mmap_sem ordering happens to never happen for this
    > filesystem?

    Yes, it is. Look at read(2) on hugetlbfs; it copies userland data
    while holding ->i_mutex. So we have

    read(2):
    mutex_lock(&A)
    down_read(&B)

    mmap(2):
    down_write(&B);
    mutex_lock(&A);

    which is an obvious deadlock.

    > So we need to pull the i_mutex out of hugetlbfs_file_mmap().

    IIRC, you have a patch in your tree doing just that...


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