netdev - Re: [PATCH v2 4/7] fs/proc/task_mmu.c: shift mm_access() from m_start() to proc_maps

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Date:	Wed, 3 Dec 2014 18:34:48 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	David Howells <dhowells@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <levinsasha928@...il.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Alexey Dobriyan <adobriyan@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v2 4/7] fs/proc/task_mmu.c: shift mm_access() from
	m_start() to proc_maps_open()

On 12/03, Kirill A. Shutemov wrote:
>
> On Tue, Aug 05, 2014 at 09:46:55PM +0200, Oleg Nesterov wrote:
> > A simple test-case from Kirill Shutemov
> >
> > 	cat /proc/self/maps >/dev/null
> > 	chmod +x /proc/self/net/packet
> > 	exec /proc/self/net/packet
> >
> > makes lockdep unhappy, cat/exec take seq_file->lock + cred_guard_mutex in
> > the opposite order.
>
> Oleg, I see it again with almost the same test-case:
>
> 	cat /proc/self/stack >/dev/null
> 	chmod +x /proc/self/net/packet
> 	exec /proc/self/net/packet

Yes, there are more lock_trace/mm_access (ab)users. Fortunately, they
are much simpler than proc/pid/maps (which also asked for other cleanups
and fixes).

I'll try to take a look, thanks for reminding.

And I agree with Eric, chmod+x probably makes no sense. Still I think
this code deserves some cleanups regardless. To the point I think that
lock_trace() should probably die.

Thanks!

Oleg.

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