Re: [PATCHSET] cpuset: decouple cpuset locking from cgroup core, take#2

[Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>]

On 2013/1/4 5:35, Tejun Heo wrote:
> Hello, guys.
> 
> This is the second attempt at decoupling cpuset locking from cgroup
> core.  Changes from the last take[L] are
> 
> * cpuset-drop-async_rebuild_sched_domains.patch moved from 0007 to
>   0009.  This reordering makes cpu hotplug handling async first and
>   removes the temporary cyclic locking dependency.
> 
> * 0006-cpuset-cleanup-cpuset-_can-_attach.patch no longer converts
>   cpumask_var_t to cpumask_t as per Rusty Russell.
> 
> * 0008-cpuset-don-t-nest-cgroup_mutex-inside-get_online_cpu.patch now
>   synchronously rebuilds sched domains from cpu hotplug callback.
>   This fixes various issues caused by confused scheduler puttings
>   tasks into a dead cpu including the RCU stall problem reported by Li
>   Zefan.
> 
> Original patchset description follows.
> 
> Depending on cgroup core locking - cgroup_mutex - is messy and makes
> cgroup prone to locking dependency problems.  The current code already
> has lock dependency loop - memcg nests get_online_cpus() inside
> cgroup_mutex.  cpuset the other way around.
> 
> Regardless of the locking details, whatever is protecting cgroup has
> inherently to be something outer to most other locking constructs.
> cgroup calls into a lot of major subsystems which in turn have to
> perform subsystem-specific locking.  Trying to nest cgroup
> synchronization inside other locks isn't something which can work
> well.
> 
> cgroup now has enough API to allow subsystems to implement their own
> locking and cgroup_mutex is scheduled to be made private to cgroup
> core.  This patchset makes cpuset implement its own locking instead of
> relying on cgroup_mutex.
> 
> cpuset is rather nasty in this respect.  Some of it seems to have come
> from the implementation history - cgroup core grew out of cpuset - but
> big part stems from cpuset's need to migrate tasks to an ancestor
> cgroup when an hotunplug event makes a cpuset empty (w/o any cpu or
> memory).
> 
> This patchset decouples cpuset locking from cgroup_mutex.  After the
> patchset, cpuset uses cpuset-specific cpuset_mutex instead of
> cgroup_mutex.  This also removes the lockdep warning triggered during
> cpu offlining (see 0009).
> 
> Note that this leaves memcg as the only external user of cgroup_mutex.
> Michal, Kame, can you guys please convert memcg to use its own locking
> too?
> 
> This patchset contains the following thirteen patches.
> 
>  0001-cpuset-remove-unused-cpuset_unlock.patch
>  0002-cpuset-remove-fast-exit-path-from-remove_tasks_in_em.patch
>  0003-cpuset-introduce-css_on-offline.patch
>  0004-cpuset-introduce-CS_ONLINE.patch
>  0005-cpuset-introduce-cpuset_for_each_child.patch
>  0006-cpuset-cleanup-cpuset-_can-_attach.patch
>  0007-cpuset-reorganize-CPU-memory-hotplug-handling.patch
>  0008-cpuset-don-t-nest-cgroup_mutex-inside-get_online_cpu.patch
>  0009-cpuset-drop-async_rebuild_sched_domains.patch
>  0010-cpuset-make-CPU-memory-hotplug-propagation-asynchron.patch
>  0011-cpuset-pin-down-cpus-and-mems-while-a-task-is-being-.patch
>  0012-cpuset-schedule-hotplug-propagation-from-cpuset_atta.patch
>  0013-cpuset-replace-cgroup_mutex-locking-with-cpuset-inte.patch
> 
> 0001-0006 are prep patches.
> 
> 0007-0009 make cpuset nest get_online_cpus() inside cgroup_mutex, not
> the other way around.
> 
> 0010-0012 plug holes which would be exposed by switching to
> cpuset-specific locking.
> 
> 0013 replaces cgroup_mutex with cpuset_mutex.
> 
> This patchset is on top of v3.8-rc2 (d1c3ed669a) and also available in
> the following git branch.
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-cpuset-locking
> 
> diffstat follows.
> 
>  kernel/cpuset.c |  760 ++++++++++++++++++++++++++++++++------------------------
>  1 file changed, 438 insertions(+), 322 deletions(-)

I've reviewed and tested the patchset, and it looks good to me!

Acked-by: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>