linux-kernel - Re: [PATCHSET cgroup/for-3.8] cgroup_freezer: allow migration regardless of freezer state and update locking

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Message-ID: <2424755.Pg0O5tTD3k@vostro.rjw.lan>
Date:	Fri, 19 Oct 2012 18:54:42 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Tejun Heo <tj@...nel.org>
Cc:	oleg@...hat.com, linux-kernel@...r.kernel.org, lizefan@...wei.com,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org
Subject: Re: [PATCHSET cgroup/for-3.8] cgroup_freezer: allow migration regardless of freezer state and update locking

On Tuesday 16 of October 2012 15:28:39 Tejun Heo wrote:
> Hello,
> 
> This patchset updates cgroup_freezer so that
> 
> * Unfreezable kernel tasks don't prevent a cgroup from transitioning
>   into FROZEN from FREEZING.  There's nothing userland can do with or
>   about such tasks.
> 
> * Tasks can be moved in and out of a frozen cgroup.  Tasks are made to
>   conform to the state of the new cgroup during migration.  This
>   behavior makes a lot more sense and removes the use of
>   ->can_attach() which makes co-mounting difficult.
> 
> * Remove use of cgroup_lock_live_group().  Grabbing cgroup_lock from
>   outside cgroup proper creates a painful locking dependency and is
>   being phased out.  With the above behavior change, removing
>   dependency on cgroup_lock is pretty easy.  IMHO, it was simply the
>   wrong behavior to implement which forced the wrong implementation.
> 
> This patchset contains the following seven patches.
> 
>  0001-cgroup-cgroup_subsys-fork-should-be-called-after-the.patch
>  0002-freezer-add-missing-mb-s-to-freezer_count-and-freeze.patch
>  0003-cgroup_freezer-make-it-official-that-writes-to-freez.patch
>  0004-cgroup_freezer-don-t-stall-transition-to-FROZEN-for-.patch
>  0005-cgroup_freezer-allow-moving-tasks-in-and-out-of-a-fr.patch
>  0006-cgroup_freezer-prepare-update_if_frozen-for-locking-.patch
>  0007-cgroup_freezer-don-t-use-cgroup_lock_live_group.patch
> 
> 0001 is a fix for a rather embarrassing bug in cgroup core.  It does
> things in the wrong order leaving a window for racing during fork.
> 
> 0002 adds a missing mb() around freezing condition updates / checks.
> 
> 0003-0004 make cgroup_freezer ignore unfreezable kernel tasks and
> handle PF_FREEZER_SKIP correctly.
> 
> 0005 allows migrating tasks in and out of a frozen cgroup.
> 
> 0006-0007 remove the use of cgroup_lock_live_group().
> 
> This patchset is on top of v3.7-rc1 and available in the following git
> branch.
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-cgroup_freezer-locking

It seems that no one has any comments. :-)

Are you going to prepare a branch for me to pull from?

Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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