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    SubjectRe: Fwd: Fw: [] BUG: dentry xattrs still in use in shrink_dcache_for_umount() with reiserfs
    Hash: SHA1

    Jeff Mahoney wrote:
    > Andrea Righi wrote:
    >> Jeff Mahoney wrote:
    >>> I have the patchset that I mentioned, but I'm not proposing it for 2.6.21.
    >>> It's much too invasive to be introduced in an -rc7, but it does include
    >>> locking changes that I believe avoid this bug.
    >>> Vladimir was right in his analysis that sometimes get_xa_root() takes the
    >>> reference once and other times twice, but not for the right reasons. I save
    >>> a reference to the xattr dir to avoid a lookup later, but when there are multiple
    >>> getxattrs or listxattrs as the first xattr operation on the file system, we can end
    >>> up taking a second reference when we shouldn't. This is because those operations
    >>> are protected by read locks and the ->xattr_root pointer isn't protected by anything
    >>> else. A quick fix would be to just extend the protection of the priv root's i_mutex
    >>> around the assignment, and test first. The right fix involves a complete rework of
    >>> the locking, and I have code to do that, it's just too late to include it in 2.6.21.
    >>> I'd love to know what Andrea (and now Andi Kleen) are doing to hit this now. There
    >>> haven't been any changes in this code in a while, and the shrink_dcache_for_umount()
    >>> has been around since October. I'm unable to reproduce locally so far, so if Andrea
    >>> or Andi could see if this fixes it for them, I'd appreciate it.
    >> Jeff, your patch doesn't resolve, but you hit the problem. Actually, I
    >> think the xattr_root pointer must be protected also in get_xa_root()
    >> using the same private root i_mutex.
    >> I've tested the following patch and it resolves in my case. What do you
    >> think about it? could it be a reasonable fix?
    > Your patch fixes the problem. That'll teach me to spin a patch up while I'm headed
    > out the door. I think a cleaner solution for now is just to refactor get_xa_root,
    > __get_xa_root, and create_xa_root into one function to simplify the lookup and the
    > locking. I think I'll add another step to my patch set that removes the caching of
    > xattr_root entirely or creates in on mount, as the priv root is created. The privroot
    > must be cached to avoid a deadlock on the fs-root directory's i_mutex, but xattr_root
    > was cached as an optimzation. If we need to take privroot->i_mutex every time, there's
    > no point in caching it since it will probably be in the dcache anyway.
    > -Jeff

    Ignore this patch. I missed a spot.

    - -Jeff

    - --
    Jeff Mahoney
    SUSE Labs
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