linux-kernel - Re: [PATCH 3/3] VFS: close race between getcwd() and d

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Date:   Thu, 9 Nov 2017 05:08:54 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Nikolay Borisov <nborisov@...e.com>
Cc:     NeilBrown <neilb@...e.com>, Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] VFS: close race between getcwd() and d_move()

On Thu, Nov 09, 2017 at 01:41:24PM +0200, Nikolay Borisov wrote:
> On  9.11.2017 05:22, NeilBrown wrote:
> > @@ -493,12 +496,18 @@ void __d_drop(struct dentry *dentry)
> >  		} else
> >  			hlist_bl_lock(b);
> >  		__hlist_bl_del(&dentry->d_hash);
> > -		dentry->d_hash.pprev = NULL;
> > +		if (likely(!moving))
> > +			dentry->d_hash.pprev = NULL;
> 
> nit: isn't a bit more explicit if (unlikely(moving)). I suspect the end
> result is the same, however it's easy to miss the !. It's not a big deal
> but just wondering.

umm ... you just suggested the exact opposite of what the patch is
intended to do.  likely()/unlikely() only hint to the compiler the
probabilities of the branch; they don't change the meaning of the
condition.