linux-kernel - Re: 2.6.25-rc9 -- INFO: possible circular locking dependency detected

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Message-ID: <20080414070234.GA7482@osiris.boeblingen.de.ibm.com>
Date:	Mon, 14 Apr 2008 09:02:34 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Miles Lane <miles.lane@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Gautham Shenoy <ego@...ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Ingo Molnar <mingo@...e.hu>
Subject: Re: 2.6.25-rc9 -- INFO: possible circular locking dependency
	detected

On Mon, Apr 14, 2008 at 08:54:05AM +0200, Peter Zijlstra wrote:
> Fun,
> 
> I will need to sort out this code before I can say anything about that,
> perhaps Gautham and or Rafael have ideas before I can come up with
> something.. ?

Why not simply removing the get/put_online_cpus() pair in sched_getaffinity?
It's superfluous since we have already a read_lock/read_unlock pair there
which does disable/enable cpu hotplug anyway.

Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
---
 kernel/sched.c |    3 ---
 1 file changed, 3 deletions(-)

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -4873,7 +4873,6 @@ long sched_getaffinity(pid_t pid, cpumas
 	struct task_struct *p;
 	int retval;
 
-	get_online_cpus();
 	read_lock(&tasklist_lock);
 
 	retval = -ESRCH;
@@ -4889,8 +4888,6 @@ long sched_getaffinity(pid_t pid, cpumas
 
 out_unlock:
 	read_unlock(&tasklist_lock);
-	put_online_cpus();
-
 	return retval;
 }
 
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