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    SubjectRe: 3.5-rc3: BUG: Dentry still in use (1) [unmount of cgroup cgroup]
    On 2012/6/30 0:58, tj@kernel.org wrote:

    > Hey,
    >
    > On Fri, Jun 29, 2012 at 10:20:11AM +0800, Li Zefan wrote:
    >>> Can you please elaborate a bit? I'm not really following? Where does
    >>> the last root->d_count-- come from?
    >>
    >>
    >> From my limited knowledge about vfs internal, seems the parent's refcnt won't go down
    >> to 0 before its children. When mkdir, the parent's refcnt will be incremented, and
    >> after rmdir, dput(subdir) will drop subdir's refcnt and then drop parent's.
    >>
    >> So when dropping the subdir's refcnt and leading the superblock to be killed, the root's
    >> dentry is still > 0.
    >
    > Heh, yeah, I thought you found who was holding out on the refcnt. :)
    >


    dput will drop both the subdir and the root's dentry refcnt, but kill_sb will be called
    inbetween.

    So it's bad to have dentry refcnts dangling after umount. I've made a patch so css will
    pin cgroup instead of cgroup dentry.



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