Messages in this thread | | | Date | Wed, 10 Dec 2008 18:36:07 +0530 | From | Balbir Singh <> | Subject | Re: [RFC][RFT] memcg fix cgroup_mutex deadlock when cpuset reclaims memory |
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* Daisuke Nishimura <d-nishimura@mtf.biglobe.ne.jp> [2008-12-10 20:53:37]:
> On Wed, 10 Dec 2008 17:18:36 +0900 > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > > > On Wed, 10 Dec 2008 16:41:26 +0900 > > Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote: > > > > > On Wed, 10 Dec 2008 15:19:48 +0900, Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote: > > > > On Wed, 10 Dec 2008 10:49:47 +0530, Balbir Singh <balbir@linux.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@linux.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 ? > > > Yes. > Thank you for explaining in detail. >
Sorry, I don't understand the context, I am unable to figure out
1. How to reproduce the problem that Daisuke-San reported 2. Whether the patch is correct or causing more problems or needs more stuff to completely fix the race.
> > Daisuke Nishimura. > > > 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 > >
-- Balbir
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