From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id AC2336B006A for ; Fri, 8 Oct 2010 21:15:33 -0400 (EDT) Received: from d01relay06.pok.ibm.com (d01relay06.pok.ibm.com [9.56.227.116]) by e8.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id o9910aSW022732 for ; Fri, 8 Oct 2010 21:00:36 -0400 Received: from d01av04.pok.ibm.com (d01av04.pok.ibm.com [9.56.224.64]) by d01relay06.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id o991FPfI1859754 for ; Fri, 8 Oct 2010 21:15:25 -0400 Received: from d01av04.pok.ibm.com (loopback [127.0.0.1]) by d01av04.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id o991FPRo010528 for ; Fri, 8 Oct 2010 21:15:25 -0400 Date: Sat, 9 Oct 2010 06:45:20 +0530 From: Balbir Singh Subject: Re: [BUGFIX] memcg CPU hotplug lockdep warning fix Message-ID: <20101009011520.GJ5327@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <20101008174958.GI5327@balbir.in.ibm.com> <20101008114123.ff0592b7.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20101008114123.ff0592b7.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org To: Andrew Morton Cc: KAMEZAWA Hiroyuki , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" List-ID: * Andrew Morton [2010-10-08 11:41:23]: > On Fri, 8 Oct 2010 23:19:58 +0530 > Balbir Singh wrote: > > > > > memcg has lockdep warnings (sleep inside rcu lock) > > > > From: Balbir Singh > > > > Recent move to get_online_cpus() ends up calling get_online_cpus() from > > mem_cgroup_read_stat(). However mem_cgroup_read_stat() is called under rcu > > lock. get_online_cpus() can sleep. The dirty limit patches expose > > this BUG more readily due to their usage of mem_cgroup_page_stat() > > > > This patch address this issue as identified by lockdep and moves the > > hotplug protection to a higher layer. This might increase the time > > required to hotplug, but not by much. > > > > Warning messages > > > > BUG: sleeping function called from invalid context at kernel/cpu.c:62 > > in_atomic(): 0, irqs_disabled(): 0, pid: 6325, name: pagetest > > 2 locks held by pagetest/6325: > > #0: (&mm->mmap_sem){......}, at: [] > > do_page_fault+0x27d/0x4a0 > > #1: (rcu_read_lock){......}, at: [] > > mem_cgroup_page_stat+0x0/0x23f > > Pid: 6325, comm: pagetest Not tainted 2.6.36-rc5-mm1+ #201 > > Call Trace: > > [] __might_sleep+0x12d/0x131 > > [] get_online_cpus+0x1c/0x51 > > [] mem_cgroup_read_stat+0x27/0xa3 > > [] mem_cgroup_page_stat+0x131/0x23f > > [] ? mem_cgroup_page_stat+0x0/0x23f > > [] global_dirty_limits+0x42/0xf8 > > [] throttle_vm_writeout+0x3a/0xb4 > > [] shrink_zone+0x3e6/0x3f8 > > [] ? ktime_get_ts+0xb2/0xbf > > [] do_try_to_free_pages+0x106/0x478 > > [] try_to_free_mem_cgroup_pages+0xe5/0x14c > > [] mem_cgroup_hierarchical_reclaim+0x314/0x3a2 > > [] __mem_cgroup_try_charge+0x29b/0x593 > > [] ? __mem_cgroup_try_charge+0xb4/0x593 > > [] ? local_clock+0x40/0x59 > > [] ? sched_clock+0x9/0xd > > [] ? sched_clock_local+0x1c/0x82 > > [] mem_cgroup_charge_common+0x4b/0x76 > > [] ? bio_add_page+0x36/0x38 > > [] mem_cgroup_cache_charge+0x1f4/0x214 > > [] add_to_page_cache_locked+0x4a/0x148 > > .... > > > > > > Signed-off-by: Balbir Singh > > --- > > > > mm/memcontrol.c | 4 ++-- > > 1 files changed, 2 insertions(+), 2 deletions(-) > > > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index 116fecd..f4c5665 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -578,7 +578,6 @@ static s64 mem_cgroup_read_stat(struct mem_cgroup *mem, > > int cpu; > > s64 val = 0; > > > > - get_online_cpus(); > > for_each_online_cpu(cpu) > > val += per_cpu(mem->stat->count[idx], cpu); > > #ifdef CONFIG_HOTPLUG_CPU > > @@ -586,7 +585,6 @@ static s64 mem_cgroup_read_stat(struct mem_cgroup *mem, > > val += mem->nocpu_base.count[idx]; > > spin_unlock(&mem->pcp_counter_lock); > > #endif > > - put_online_cpus(); > > return val; > > } > > > > @@ -1284,6 +1282,7 @@ s64 mem_cgroup_page_stat(enum mem_cgroup_read_page_stat_item item) > > struct mem_cgroup *iter; > > s64 value; > > > > + get_online_cpus(); > > rcu_read_lock(); > > mem = mem_cgroup_from_task(current); > > if (mem && !mem_cgroup_is_root(mem)) { > > @@ -1305,6 +1304,7 @@ s64 mem_cgroup_page_stat(enum mem_cgroup_read_page_stat_item item) > > } else > > value = -EINVAL; > > rcu_read_unlock(); > > + put_online_cpus(); > > > > return value; > > } > > Confused again. There's no mem_cgroup_page_stat() in mainline, > linux-next or in any patches in -mm. > Oops, sorry for the confusion. This patch applies on top of the dirty limit patches posted by Greg. I should have posted this in response to Greg's posting. -- Three Cheers, Balbir -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org