Re: [PATCH] dcache d_drop() bug fix / __d_drop() use fix

[Ian Kent]

On Wed, 16 Feb 2005, Jeff Moyer wrote:

> ==> Regarding Re: [PATCH] dcache d_drop() bug fix / __d_drop() use fix; raven@xxxxxxxxxx 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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