linux-kernel - Re: [PATCH] Add a refcount check in dput()

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Message-Id: <20070917134835.88c8f470.akpm@linux-foundation.org>
Date:	Mon, 17 Sep 2007 13:48:35 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Paul Menage" <menage@...gle.com>
Cc:	viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Add a refcount check in dput()

On Mon, 17 Sep 2007 11:21:35 -0700
"Paul Menage" <menage@...gle.com> wrote:

> On 9/15/07, Andrew Morton <akpm@...ux-foundation.org> wrote:
> > >
> > > +     BUG_ON(!atomic_read(&dentry->d_count));
> > >  repeat:
> > >       if (atomic_read(&dentry->d_count) == 1)
> > >               might_sleep();
> >
> > eek, much too aggressive.
> 
> How about the equivalent BUG_ON() in dget()? I figure that they ought
> to both be of the same strictness.

The one in dget() is known not to trigger - it's been there for a long time.

My problem with new BUG_ON's is that they get added thinking "no way will
this trigger" and lo, they do trigger and lots of people get their testing
disrupted for a whole release.

Long-standing checks like the one in dget() should perhaps be removed now
that we know they don't trigger - move them under some CONFIG_DEBUG_foo
option.
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