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Date: Tue, 3 Aug 2010 19:48:20 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
cc: David Howells <dhowells@redhat.com>, Oleg Nesterov <oleg@redhat.com>,
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        Jiri Olsa <jolsa@redhat.com>
Subject: Re: [PATCH 2/2] CRED: Fix __task_cred()'s lockdep check and banner
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On Tue, 3 Aug 2010, Linus Torvalds wrote:

> Added Oleg and Thomas to the participants.
> 
> Oleg/Thomas: the whole thread is on lkml, but I'm quoting most of the
> relevant parts..
> 
> On Tue, Aug 3, 2010 at 2:34 AM, David Howells <dhowells@redhat.com> wrote:
> >
> > A previous patch:
> >
> >        commit 8f92054e7ca1d3a3ae50fb42d2253ac8730d9b2a
> >        Author: David Howells <dhowells@redhat.com>
> >        Date:   Thu Jul 29 12:45:55 2010 +0100
> >        Subject: CRED: Fix __task_cred()'s lockdep check and banner comment
> >
> > fixed the lockdep checks on __task_cred().  This has shown up a place in the
> > signalling code where a lock should be held - namely that
> > check_kill_permission() requires its callers to hold the RCU lock.
> 
> It's not just check_kill_permission(), is it? I thought we could do
> the "for_each_process()" loops with just RCU, rather than holding the
> whole tasklist_lock? So I _think_ that getting the RCU read-lock would
> make it possible to get rid of the tasklist_lock in there too? At
> least in kill_something_info().
> 
> Yes/no? What am I missing? This is an Oleg question, mainly.

Yes, almost all places in the kernel which hold tasklist_lock read
locked are safe with RCU. I started to work on that, but got
distracted.
 
Thanks,

	tglx
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