[BUGFIX][PATCH] memcg rcu lock fix v2

[KAMEZAWA Hiroyuki]

On Fri, 23 Apr 2010 11:55:16 +0800
Li Zefan <lizf@xxxxxxxxxxxxxx> wrote:

> Li Zefan wrote:
> > KAMEZAWA Hiroyuki wrote:
> >> On Fri, 23 Apr 2010 11:00:41 +0800
> >> Li Zefan <lizf@xxxxxxxxxxxxxx> 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 ? 
> > 
> > Yes, and I did some more simple tests on memcg, no more warning
> > showed up.
> > 
> 
> oops, after trigging oom, I saw 2 more warnings:
> 

Thank you for good testing.
=
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

css_id() should be called under rcu_read_lock().
And css_is_ancestor() 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@xxxxxxxxxxxxxx>
Cc: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Cc: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
 mm/memcontrol.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

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
@@ -838,10 +838,12 @@ int task_in_mem_cgroup(struct task_struc
 	 * enabled in "curr" and "curr" is a child of "mem" in *cgroup*
 	 * hierarchy(even if use_hierarchy is disabled in "mem").
 	 */
+	rcu_read_lock();
 	if (mem->use_hierarchy)
 		ret = css_is_ancestor(&curr->css, &mem->css);
 	else
 		ret = (curr == mem);
+	rcu_read_unlock();
 	css_put(&curr->css);
 	return ret;
 }
@@ -1360,9 +1362,13 @@ static int memcg_oom_wake_function(wait_
 	 * Both of oom_wait_info->mem and wake_mem are stable under us.
 	 * Then we can use css_is_ancestor without taking care of RCU.
 	 */
+	rcu_read_lock();
 	if (!css_is_ancestor(&oom_wait_info->mem->css, &wake_mem->css) &&
-	    !css_is_ancestor(&wake_mem->css, &oom_wait_info->mem->css))
+	    !css_is_ancestor(&wake_mem->css, &oom_wait_info->mem->css)) {
+		rcu_read_unlock();
 		return 0;
+	}
+	rcu_read_unlock();
 
 wakeup:
 	return autoremove_wake_function(wait, mode, sync, arg);
@@ -2401,7 +2407,9 @@ 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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