linux-kernel - Re: [PATCH 2/2] CRED: Fix __task_cred()'s lockdep check and banner comment

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Message-Id: <201008040038.o740cg2E031196@www262.sakura.ne.jp>
Date:	Wed, 04 Aug 2010 09:38:42 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	dhowells@...hat.com
Cc:	paulmck@...ux.vnet.ibm.com, torvalds@...l.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, jolsa@...hat.com
Subject: Re: [PATCH 2/2] CRED: Fix __task_cred()'s lockdep check and banner comment

David Howells wrote:
> Tetsuo Handa wrote:
> 
> > I got below warning. Is this related to this patch?
> > 
> > [  140.173556] ===================================================
> > [  140.215379] [ INFO: suspicious rcu_dereference_check() usage. ]
> > [  140.216461] ---------------------------------------------------
> > [  140.217530] kernel/signal.c:660 invoked rcu_dereference_check() without protection!
> 
> Yes.  The patch has uncovered a case of where we should be holding a lock, but
> aren't.
> 
> Can you try the attached patch?
> 
> David
> ---
> From: David Howells <dhowells@...hat.com>
> Subject: [PATCH] CRED: Fix RCU warning due to previous patch fixing __task_cred()'s checks
> 
> A previous patch:
> 
> 	commit 8f92054e7ca1d3a3ae50fb42d2253ac8730d9b2a
> 	Author: David Howells <dhowells@...hat.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 may be that it would be better to add RCU read lock calls in
> group_send_sig_info() only, around the call to check_kill_permission().  On the
> other hand, some of the callers are either holding the RCU read lock already,
> or have disabled interrupts, in which case, it's just extra overhead to do it
> in g_s_s_i().

That patch solved the warning. Thank you.
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