linux-kernel - Re: fs: NULL deref in atime_needs

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Date:	Mon, 29 Feb 2016 16:50:31 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dmitry Vyukov <dvyukov@...gle.com>, Ian Kent <raven@...maw.net>,
	Mickaël Salaün <mic@...ikod.net>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	David Howells <dhowells@...hat.com>
Subject: Re: fs: NULL deref in atime_needs_update

On Mon, Feb 29, 2016 at 08:45:37AM -0800, Linus Torvalds wrote:

> > David, Linus, do you see any problems with that?  To me it looks saner
> > that way and as cheap as the current code, but I might be missing something
> > here...
> 
> I'd absolutely love to see this. The memory ordering for the flags
> updates and reading was always really confusing, and I hated how it
> was hidden inside the random access functions. And apparently it
> wasn't just confusing, it was buggy too.
> 
> But I'd love it _more_ if this also means that we can get rid of the
> rmb's, which your patch didn't. Can we? Or does the ordering still
> remain for some other issue?

In __d_entry_type(), you mean?  Should be, along with READ_ONCE() there.
AFAICS, ordering shouldn't be an issue anymore...