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Message-ID: <31051.10.75.179.61.1228908723.squirrel@webmail-b.css.fujitsu.com>
Date: Wed, 10 Dec 2008 20:32:03 +0900 (JST)
From: "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
To: balbir@...ux.vnet.ibm.com
Cc: "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
menage@...gle.com,
"KAMEZAWA Hiroyuki" <kamezawa.hiroyuki@...fujitsu.com>,
"Daisuke Miyakawa" <dmiyakawa@...gle.com>,
"YAMAMOTO Takashi" <yamamoto@...inux.co.jp>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC][RFT] memcg fix cgroup_mutex deadlock when cpusetreclaims
memory
Balbir Singh said:
> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2008-12-10
> 17:49:06]:
>
>> On Wed, 10 Dec 2008 10:49:47 +0530
>> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
>>
>> > Hi,
>> >
>> > Here is a proposed fix for the memory controller cgroup_mutex deadlock
>> > reported. It is lightly tested and reviewed. I need help with review
>> > and test. Is the reported deadlock reproducible after this patch? A
>> > careful review of the cpuset impact will also be highly appreciated.
>> >
>> > From: Balbir Singh <balbir@...ux.vnet.ibm.com>
>> >
>> > cpuset_migrate_mm() holds cgroup_mutex throughout the duration of
>> > do_migrate_pages(). The issue with that is that
>> >
>> > 1. It can lead to deadlock with memcg, as do_migrate_pages()
>> > enters reclaim
>> > 2. It can lead to long latencies, preventing users from creating/
>> > destroying other cgroups anywhere else
>> >
>> > The patch holds callback_mutex through the duration of
>> cpuset_migrate_mm() and
>> > gives up cgroup_mutex while doing so.
>> >
>> > Signed-off-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
>> > ---
>> >
>> > include/linux/cpuset.h | 13 ++++++++++++-
>> > kernel/cpuset.c | 23 ++++++++++++-----------
>> > 2 files changed, 24 insertions(+), 12 deletions(-)
>> >
>> > diff -puN kernel/cgroup.c~cpuset-remove-cgroup-mutex-from-update-path
>> kernel/cgroup.c
>> > diff -puN kernel/cpuset.c~cpuset-remove-cgroup-mutex-from-update-path
>> kernel/cpuset.c
>> > --- a/kernel/cpuset.c~cpuset-remove-cgroup-mutex-from-update-path
>> > +++ a/kernel/cpuset.c
>> > @@ -369,7 +369,7 @@ static void guarantee_online_mems(const
>> > * task has been modifying its cpuset.
>> > */
>> >
>> > -void cpuset_update_task_memory_state(void)
>> > +void __cpuset_update_task_memory_state(bool held)
>> > {
>> > int my_cpusets_mem_gen;
>> > struct task_struct *tsk = current;
>> > @@ -380,7 +380,8 @@ void cpuset_update_task_memory_state(voi
>> > rcu_read_unlock();
>> >
>> > if (my_cpusets_mem_gen != tsk->cpuset_mems_generation) {
>> > - mutex_lock(&callback_mutex);
>> > + if (!held)
>> > + mutex_lock(&callback_mutex);
>> > task_lock(tsk);
>> > cs = task_cs(tsk); /* Maybe changed when task not locked */
>> > guarantee_online_mems(cs, &tsk->mems_allowed);
>> > @@ -394,7 +395,8 @@ void cpuset_update_task_memory_state(voi
>> > else
>> > tsk->flags &= ~PF_SPREAD_SLAB;
>> > task_unlock(tsk);
>> > - mutex_unlock(&callback_mutex);
>> > + if (!held)
>> > + mutex_unlock(&callback_mutex);
>> > mpol_rebind_task(tsk, &tsk->mems_allowed);
>> > }
>> > }
>> > @@ -949,13 +951,15 @@ static int update_cpumask(struct cpuset
>> > * so that the migration code can allocate pages on these nodes.
>> > *
>> > * Call holding cgroup_mutex, so current's cpuset won't change
>> > - * during this call, as manage_mutex holds off any cpuset_attach()
>> > + * during this call, as callback_mutex holds off any
>> cpuset_attach()
>> > * calls. Therefore we don't need to take task_lock around the
>> > * call to guarantee_online_mems(), as we know no one is changing
>> > * our task's cpuset.
>> > *
>> > * Hold callback_mutex around the two modifications of our tasks
>> > - * mems_allowed to synchronize with cpuset_mems_allowed().
>> > + * mems_allowed to synchronize with cpuset_mems_allowed(). Give
>> > + * up cgroup_mutex to avoid deadlocking with other subsystems
>> > + * as we enter reclaim from do_migrate_pages().
>> > *
>> > * While the mm_struct we are migrating is typically from some
>> > * other task, the task_struct mems_allowed that we are hacking
>> > @@ -976,17 +980,14 @@ static void cpuset_migrate_mm(struct mm_
>> > {
>> > struct task_struct *tsk = current;
>> >
>> > - cpuset_update_task_memory_state();
>> > -
>> > + cgroup_unlock();
>> > mutex_lock(&callback_mutex);
>> > + cpuset_update_task_memory_state_locked();
>> > tsk->mems_allowed = *to;
>> > - mutex_unlock(&callback_mutex);
>> > -
>> > do_migrate_pages(mm, from, to, MPOL_MF_MOVE_ALL);
>> > -
>> > - mutex_lock(&callback_mutex);
>> > guarantee_online_mems(task_cs(tsk),&tsk->mems_allowed);
>> > mutex_unlock(&callback_mutex);
>> > + cgroup_lock();
>> > }
>> >
>>
>> Hmm...can't this happen ?
>>
>> Assume there is a task X and cgroup Z1 and Z2. Z1 and Z2 doesn't need to
>> be in
>> the same hierarchy.
>> ==
>> CPU A attach task X to cgroup Z1
>> cgroup_lock()
>> for_each_subsys_state()
>
> You mean for_each_subsys() right?
>
>> => attach(X,Z)
>> => migrate_mm()
>> => cgroup_unlock()
>> migration
>>
>> CPU B attach task X to cgroup Z2 at the same time
>> cgroup_lock()
>> replace css_set.
>> ==
>>
>> Works on CPU B can't break for_each_subsys_state() in CPU A ?
>>
>
> for_each_subsys is hierarchy aware, so if we try to add the same task
> to different hierachies, it should not be a problem right?
>
Ah, maybe. But what happens when Z1 and Z2 is the same hierarchy ?
Are there some locks ?
-Kame
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