linux-kernel - Re: 2.6.39-rc4+: Kernel leaking memory during FS scanning, regression?

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Date:	Tue, 26 Apr 2011 19:09:18 +0200
From:	Bruno Prémont <bonbons@...ux-vserver.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Mike Frysinger <vapier.adi@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	Pekka Enberg <penberg@...nel.org>
Subject: Re: 2.6.39-rc4+: Kernel leaking memory during FS scanning,
 regression?

On Tue, 26 April 2011 Bruno Prémont <bonbons@...ux-vserver.org> wrote:
> On Tue, 26 April 2011 "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> > On Tue, Apr 26, 2011 at 08:19:04AM +0200, Bruno Prémont wrote:
> > > Though I will use the few minutes I have this evening to try to fetch
> > > kernel traces of running tasks with sysrq+t which may eventually give
> > > us a hint at where rcu_thread is stuck/waiting.
> > 
> > This would be very helpful to me!
> 
> Here it comes:
> 
> rcu_kthread (when build processes are STOPped):
> [  836.050003] rcu_kthread     R running   7324     6      2 0x00000000
> [  836.050003]  dd473f28 00000046 5a000240 dd65207c dd407360 dd651d40 0000035c dd473ed8
> [  836.050003]  c10bf8a2 c14d63d8 dd65207c dd473f28 dd445040 dd445040 dd473eec c10be848
> [  836.050003]  dd651d40 dd407360 ddfdca00 dd473f14 c10bfde2 00000000 00000001 000007b6
> [  836.050003] Call Trace:
> [  836.050003]  [<c10bf8a2>] ? check_object+0x92/0x210
> [  836.050003]  [<c10be848>] ? init_object+0x38/0x70
> [  836.050003]  [<c10bfde2>] ? free_debug_processing+0x112/0x1f0
> [  836.050003]  [<c103d9fd>] ? lock_timer_base+0x2d/0x70
> [  836.050003]  [<c13c8ec7>] schedule_timeout+0x137/0x280
> [  836.050003]  [<c10c02b8>] ? kmem_cache_free+0xe8/0x140
> [  836.050003]  [<c103db60>] ? sys_gettid+0x20/0x20
> [  836.050003]  [<c13c9064>] schedule_timeout_interruptible+0x14/0x20
> [  836.050003]  [<c10736e0>] rcu_kthread+0xa0/0xc0
> [  836.050003]  [<c104de00>] ? wake_up_bit+0x70/0x70
> [  836.050003]  [<c1073640>] ? rcu_process_callbacks+0x60/0x60
> [  836.050003]  [<c104d874>] kthread+0x74/0x80
> [  836.050003]  [<c104d800>] ? flush_kthread_worker+0x90/0x90
> [  836.050003]  [<c13caeb6>] kernel_thread_helper+0x6/0xd
> 
> a few minutes later when build processes have been killed:
> [  966.930008] rcu_kthread     R running   7324     6      2 0x00000000
> [  966.930008]  dd473f28 00000046 5a000240 dd65207c dd407360 dd651d40 0000035c dd473ed8
> [  966.930008]  c10bf8a2 c14d63d8 dd65207c dd473f28 dd445040 dd445040 dd473eec c10be848
> [  966.930008]  dd651d40 dd407360 ddfdca00 dd473f14 c10bfde2 00000000 00000001 000007b6
> [  966.930008] Call Trace:
> [  966.930008]  [<c10bf8a2>] ? check_object+0x92/0x210
> [  966.930008]  [<c10be848>] ? init_object+0x38/0x70
> [  966.930008]  [<c10bfde2>] ? free_debug_processing+0x112/0x1f0
> [  966.930008]  [<c103d9fd>] ? lock_timer_base+0x2d/0x70
> [  966.930008]  [<c13c8ec7>] schedule_timeout+0x137/0x280
> [  966.930008]  [<c10c02b8>] ? kmem_cache_free+0xe8/0x140
> [  966.930008]  [<c103db60>] ? sys_gettid+0x20/0x20
> [  966.930008]  [<c13c9064>] schedule_timeout_interruptible+0x14/0x20
> [  966.930008]  [<c10736e0>] rcu_kthread+0xa0/0xc0
> [  966.930008]  [<c104de00>] ? wake_up_bit+0x70/0x70
> [  966.930008]  [<c1073640>] ? rcu_process_callbacks+0x60/0x60
> [  966.930008]  [<c104d874>] kthread+0x74/0x80
> [  966.930008]  [<c104d800>] ? flush_kthread_worker+0x90/0x90
> [  966.930008]  [<c13caeb6>] kernel_thread_helper+0x6/0xd
> 
> Attached (gzipped) the complete dmesg log (dmesg-t1 contains dmesg from boot until
> after first sysrq+t  -- dmesg-t2 the output of sysrq+t 2 minutes later
> after having killed build processes).
> Just in case, I joined slabinfo.
> Ten minutes later rcu_kthread trace has not changed at all.

Just in case, /proc/$(pidof rcu_kthread)/status shows ~20k voluntary
context switches and exactly one non-voluntary one.

In addition when rcu_kthread has stopped doing its work
`swapoff $(swapdevice)` seems to block forever (at least normal shutdown
blocks on disabling swap device).
If I get to do it when I get back home I will manually try to swapoff
and take process traces with sysrq-t.

Bruno
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