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

From: Oleg Nesterov
Date: Wed Dec 03 2014 - 12:35:39 EST

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.



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