linux-kernel - [BUGFIX][PATCH] memcg rcu lock fix in swap code (Was Re: [BUG] an RCU warning in memcg

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Message-Id: <20100423121424.ae47efcb.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 23 Apr 2010 12:14:24 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: [BUGFIX][PATCH] memcg rcu lock fix in swap code (Was Re: [BUG] an
 RCU warning in memcg

On Fri, 23 Apr 2010 11:00:41 +0800
Li Zefan <lizf@...fujitsu.com> wrote:

> with CONFIG_PROVE_RCU=y, I saw this warning, it's because
> css_id() is not under rcu_read_lock().
> 

Ok. Thank you for reporting.
This is ok ? 
==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

css_id() should be called under rcu_read_lock().
Following is a report from Li Zefan.
==
===================================================
[ INFO: suspicious rcu_dereference_check() usage. ]
---------------------------------------------------
kernel/cgroup.c:4438 invoked rcu_dereference_check() without protection!

other info that might help us debug this:


rcu_scheduler_active = 1, debug_locks = 1
1 lock held by kswapd0/31:
 #0:  (swap_lock){+.+.-.}, at: [<c05058bb>] swap_info_get+0x4b/0xd0

stack backtrace:
Pid: 31, comm: kswapd0 Not tainted 2.6.34-rc5-tip+ #13
Call Trace:
 [<c083c5d6>] ? printk+0x1d/0x1f
 [<c0480744>] lockdep_rcu_dereference+0x94/0xb0
 [<c049d6ed>] css_id+0x5d/0x60
 [<c05165a5>] mem_cgroup_uncharge_swapcache+0x45/0xa0
 [<c0505e4f>] swapcache_free+0x3f/0x60
 [<c04e79e2>] __remove_mapping+0xb2/0xf0
 [<c04e7cbb>] shrink_page_list+0x26b/0x490
 [<c047f85d>] ? put_lock_stats+0xd/0x30
 [<c083fd67>] ? _raw_spin_unlock_irq+0x27/0x50
 [<c0482566>] ? trace_hardirqs_on_caller+0xb6/0x220
 [<c04e8158>] shrink_inactive_list+0x278/0x620
 [<c04729e1>] ? sched_clock_cpu+0x121/0x180
 [<c047e9b8>] ? trace_hardirqs_off_caller+0x18/0x130
 [<c047eadb>] ? trace_hardirqs_off+0xb/0x10
 [<c0843438>] ? sub_preempt_count+0x8/0x90
 [<c047f85d>] ? put_lock_stats+0xd/0x30
 [<c04e8704>] shrink_zone+0x204/0x3c0
 [<c083fcac>] ? _raw_spin_unlock+0x2c/0x50
 [<c04e951e>] kswapd+0x61e/0x7c0
 [<c04e6ed0>] ? isolate_pages_global+0x0/0x1f0
 [<c046bae0>] ? autoremove_wake_function+0x0/0x50
 [<c04e8f00>] ? kswapd+0x0/0x7c0
 [<c046b5e4>] kthread+0x74/0x80
 [<c046b570>] ? kthread+0x0/0x80
 [<c04035ba>] kernel_thread_helper+0x6/0x10

Reported-by: Li Zefan <lizf@...fujitsu.com>
Cc: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc: Balbir Singh <balbir@...ux.vnet.ibm.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
 mm/memcontrol.c |    2 ++
 1 file changed, 2 insertions(+)

Index: linux-2.6.34-rc5-mm1/mm/memcontrol.c
===================================================================
--- linux-2.6.34-rc5-mm1.orig/mm/memcontrol.c
+++ linux-2.6.34-rc5-mm1/mm/memcontrol.c
@@ -2401,7 +2401,9 @@ mem_cgroup_uncharge_swapcache(struct pag
 
 	/* record memcg information */
 	if (do_swap_account && swapout && memcg) {
+		rcu_read_lock();
 		swap_cgroup_record(ent, css_id(&memcg->css));
+		rcu_read_unlock();
 		mem_cgroup_get(memcg);
 	}
 	if (swapout && memcg)

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