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    SubjectRe: [PATCH] dcache d_drop() bug fix / __d_drop() use fix
    On Wed, 16 Feb 2005, Jeff Moyer wrote:

    > ==> Regarding Re: [PATCH] dcache d_drop() bug fix / __d_drop() use fix; raven@themaw.net adds:
    >
    > raven> On Wed, 16 Feb 2005, Jan Blunck wrote:
    > >> This is a re-submission of the patch I sent about a month ago.
    > >>
    > >> While working on my code I realized that d_drop() might race against
    > >> __d_lookup(). __d_drop() (which is called by d_drop() after acquiring the
    > >> dcache_lock) is accessing dentry->d_flags to set the DCACHE_UNHASHED flag.
    > >> This shouldn't be done without holding dentry->d_lock, like stated in
    > >> dcache.h:
    > >>
    > >> struct dentry {
    > >> ...
    > >> unsigned int d_flags; /* protected by d_lock */
    > >> ...
    > >> };
    > >>
    > >> Therefore d_drop() must acquire the dentry->d_lock. Likewise every use of
    > >> __d_drop() must acquire that lock.
    > >>
    > >> This patch fixes d_drop() and every grep'able __d_drop() use. This patch is
    > >> against today's http://linux.bkbits.net/linux-2.5.
    > >>
    >
    > raven> For my part, in autofs4, I would prefer:
    >
    > > --- linux-2.6.9/fs/autofs4/root.c.d_lock 2005-02-16 23:15:18.000000000 +0800
    > > +++ linux-2.6.9/fs/autofs4/root.c 2005-02-16 23:15:35.000000000 +0800
    > > @@ -621,7 +621,7 @@
    > > spin_unlock(&dcache_lock);
    > > return -ENOTEMPTY;
    > > }
    > > - __d_drop(dentry);
    > > + d_drop(dentry);
    > > spin_unlock(&dcache_lock);
    >
    > > dput(ino->dentry);
    >
    > Ian, this would deadlock. You already hold the dcache lock here, and
    > d_drop takes it:

    Ha!

    Yes. There is a difference between d_lock and dcache_lock.
    I need glasses!

    Please ignore what I said.

    Ian

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