linux-kernel - Re: [Bug #10815] 2.6.26-rc4: RIP find_pid

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Message-ID: <20080615033001.GE26421@linux.vnet.ibm.com>
Date:	Sat, 14 Jun 2008 20:30:01 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	Oleg Nesterov <oleg@...sign.ru>, Adrian Bunk <bunk@...nel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [Bug #10815] 2.6.26-rc4: RIP find_pid_ns+0x6b/0xa0

On Sat, Jun 14, 2008 at 11:43:38PM +0400, Alexey Dobriyan wrote:
> On Sat, Jun 14, 2008 at 11:12:12AM -0700, Paul E. McKenney wrote:
> > On Sat, Jun 14, 2008 at 06:58:39PM +0400, Oleg Nesterov wrote:
> > > On 06/14, Paul E. McKenney wrote:
> > > >
> > > > On Fri, Jun 13, 2008 at 04:52:55PM +0300, Adrian Bunk wrote:
> > > > > On Sat, Jun 07, 2008 at 10:42:57PM +0200, Rafael J. Wysocki wrote:
> > > > > > This message has been generated automatically as a part of a report
> > > > > > of recent regressions.
> > > > > > 
> > > > > > The following bug entry is on the current list of known regressions
> > > > > > from 2.6.25.  Please verify if it still should be listed.
> > > > > > 
> > > > > > 
> > > > > > Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=10815
> > > > > > Subject		: 2.6.26-rc4: RIP find_pid_ns+0x6b/0xa0
> > > > > > Submitter	: Alexey Dobriyan <adobriyan@...il.com>
> > > > > > Date		: 2008-05-27 09:23 (12 days old)
> > > > > > References	: http://lkml.org/lkml/2008/5/27/9
> > > > > > Handled-By	: Oleg Nesterov <oleg@...sign.ru>
> > > > > > 		  Linus Torvalds <torvalds@...ux-foundation.org>
> > > > > > 		  Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > > > > > Patch		: http://lkml.org/lkml/2008/5/28/16
> > > > > 
> > > > > What happened with this issue?
> > > > 
> > > > The patch listed above works for me, passes rcutorture, &c.  However,
> > > > I never have been able to reproduce the original problem, so cannot say
> > > > whether it qualifies as a fix.
> > > 
> > > I doubt very much RCU was the reason of this problem.
> > 
> > Although I very much appreciate your confidence in my code, it is new
> > code, so therefore under suspicion.
> > 
> > > Alexey, how did you trigger this problem?
> > 
> > One of them involved running LTP while doing 170 kernel builds in
> > parallel.
> 
> My gut feeling is that find_pid_ns oops, __d_lookup oops and
> __call_for_each_cic oops are the same bug.
> 
> And rcutorture failures I've mentioned to Paul privately.

Yep, running rcutorture in parallel with LTP, which didn't reproduce
for me either.

Did the patch at http://lkml.org/lkml/2008/5/28/16 help?

> Oleg, debugging you've posted never triggered.
> 
> kerneloops suggests that I'm alone. :-(

Assuming that the above patch didn't help...  As a desperation measure,
I could suggest the following patch.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---

 rcupreempt.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -urpNa -X dontdiff linux-2.6.26-rc4/kernel/rcupreempt.c linux-2.6.26-rc4-alexey/kernel/rcupreempt.c
--- linux-2.6.26-rc4/kernel/rcupreempt.c	2008-05-30 04:39:01.000000000 -0700
+++ linux-2.6.26-rc4-alexey/kernel/rcupreempt.c	2008-06-14 20:24:53.000000000 -0700
@@ -77,7 +77,7 @@
  *
  * GP in GP_STAGES stands for Grace Period ;)
  */
-#define GP_STAGES    2
+#define GP_STAGES    3
 struct rcu_data {
 	spinlock_t	lock;		/* Protect rcu_data fields. */
 	long		completed;	/* Number of last completed batch. */
--
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