linux-kernel - Re: Dcache oops

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Message-ID: <20160603214630.GU14480@ZenIV.linux.org.uk>
Date:	Fri, 3 Jun 2016 22:46:31 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Oleg Drokin <green@...uxhacker.ru>
Cc:	"<linux-kernel@...r.kernel.org> Mailing List" 
	<linux-kernel@...r.kernel.org>,
	"<linux-fsdevel@...r.kernel.org>" <linux-fsdevel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Dcache oops

On Fri, Jun 03, 2016 at 05:17:06PM -0400, Oleg Drokin wrote:

> > Can the same thing be reproduced (with NFS fix) on v4.6, ede4090, 7f427d3,
> > 4e8440b?
> 
> Well, that was faster than I expected. 4e8440b triggers right away, so I guess
> there's no point in trying the later ones?
> BTW, just to confirm you are noticing - this is a DEBUG_PAGEALLOC build,
> so all freed memory is unmapped which is likely causing this oops - as a sign
> of use after free.
 
> [   54.990119] BUG: unable to handle kernel paging request at ffff8800d2b7f000

Again a page-aligned nd->last.name and even smaller nd->last.len.  It smells
like a page that used to contain a symlink body, but got freed under us.