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Date: Wed, 10 Dec 2008 17:18:36 +0900 From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> To: Daisuke Nishimura <nishimura@....nes.nec.co.jp> Cc: balbir@...ux.vnet.ibm.com, menage@...gle.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 cpuset reclaims memory On Wed, 10 Dec 2008 16:41:26 +0900 Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote: > On Wed, 10 Dec 2008 15:19:48 +0900, Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote: > > 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. > > > > > I agree changing cpuset_migrate_mm not to hold cgroup_mutex to fix the dead lock > > is one choice, and it looks good to me at the first impression. > > > > But I'm not sure it's good to change cpuset(other subsystem) code because of memcg. > > > > Anyway, I'll test this patch and report the result tomorrow. > > (Sorry, I don't have enough time today.) > > > Unfortunately, this patch doesn't seem enough. > > This patch can fix dead lock caused by "circular lock of cgroup_mutex", > but cannot that of caused by "race between page reclaim and cpuset_attach(mpol_rebind_mm)". > > (The dead lock I fixed in memcg-avoid-dead-lock-caused-by-race-between-oom-and-cpuset_attach.patch > was caused by "race between memcg's oom and mpol_rebind_mm, and was independent of hierarchy.) > > I attach logs I got in testing this patch. > Hmm, ok then, what you mention to is this race. -- cgroup_lock() -> cpuset_attach() -> down_write(&mm->mmap_sem); down_read() -> page fault -> reclaim in memcg -> cgroup_lock(). -- What this patch tries to fix is this recursive locks -- cgroup_lock() -> cpuset_attach() -> cpuset_migrate_mm() -> charge to migration -> go to reclaim and meet cgroup_lock. -- Right ? BTW, releasing cgroup_lock() while attach() is going on is finally safe ? If not, can this lock for attach be replaced with (new) cgroup private mutex ? a new mutex like this ? -- struct cgroup { ..... mutex_t attach_mutex; /* for serializing attach() ops. while attach() is going on, rmdir() will fail */ } -- Do we need the big lock of cgroup_lock for attach(), at last ? -Kame -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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