linux-kernel - Re: [PATCH v21 015/100] cgroup freezer: Update stale locking comments

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Date:	Thu, 06 May 2010 17:25:04 -0400
From:	Oren Laadan <orenl@...columbia.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, Serge Hallyn <serue@...ibm.com>,
	Matt Helsley <matthltc@...ibm.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Cedric Le Goater <legoater@...e.fr>,
	Paul Menage <menage@...gle.com>,
	Li Zefan <lizf@...fujitsu.com>,
	linux-pm@...ts.linux-foundation.org
Subject: Re: [PATCH v21 015/100] cgroup freezer: Update stale locking comments


On 05/06/2010 03:40 PM, Rafael J. Wysocki wrote:
> On Saturday 01 May 2010, Oren Laadan wrote:
>> From: Matt Helsley <matthltc@...ibm.com>
>>
>> Update stale comments regarding locking order and add a little more detail
>> so it's easier to follow the locking between the cgroup freezer and the
>> power management freezer code.
> 
> I guess these three patches are for me.
> 
> Do you want me to handle them?

Yes, please, that would be great.

Thanks,

Oren.

> 
> Rafael
> 
> 
>> Signed-off-by: Matt Helsley <matthltc@...ibm.com>
>> Cc: Oren Laadan <orenl@...columbia.edu>
>> Cc: Cedric Le Goater <legoater@...e.fr>
>> Cc: Paul Menage <menage@...gle.com>
>> Cc: Li Zefan <lizf@...fujitsu.com>
>> Cc: Rafael J. Wysocki <rjw@...k.pl>
>> Cc: linux-pm@...ts.linux-foundation.org
>> ---
>>  kernel/cgroup_freezer.c |   21 +++++++++++++--------
>>  1 files changed, 13 insertions(+), 8 deletions(-)
>>
>> diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
>> index da5e139..85f19cc 100644
>> --- a/kernel/cgroup_freezer.c
>> +++ b/kernel/cgroup_freezer.c
>> @@ -89,10 +89,10 @@ struct cgroup_subsys freezer_subsys;
>>  
>>  /* Locks taken and their ordering
>>   * ------------------------------
>> - * css_set_lock
>>   * cgroup_mutex (AKA cgroup_lock)
>> - * task->alloc_lock (AKA task_lock)
>>   * freezer->lock
>> + * css_set_lock
>> + * task->alloc_lock (AKA task_lock)
>>   * task->sighand->siglock
>>   *
>>   * cgroup code forces css_set_lock to be taken before task->alloc_lock
>> @@ -100,33 +100,38 @@ struct cgroup_subsys freezer_subsys;
>>   * freezer_create(), freezer_destroy():
>>   * cgroup_mutex [ by cgroup core ]
>>   *
>> - * can_attach():
>> - * cgroup_mutex
>> + * freezer_can_attach():
>> + * cgroup_mutex (held by caller of can_attach)
>>   *
>> - * cgroup_frozen():
>> + * cgroup_freezing_or_frozen():
>>   * task->alloc_lock (to get task's cgroup)
>>   *
>>   * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
>> - * task->alloc_lock (to get task's cgroup)
>>   * freezer->lock
>>   *  sighand->siglock (if the cgroup is freezing)
>>   *
>>   * freezer_read():
>>   * cgroup_mutex
>>   *  freezer->lock
>> + *   write_lock css_set_lock (cgroup iterator start)
>> + *    task->alloc_lock
>>   *   read_lock css_set_lock (cgroup iterator start)
>>   *
>>   * freezer_write() (freeze):
>>   * cgroup_mutex
>>   *  freezer->lock
>> + *   write_lock css_set_lock (cgroup iterator start)
>> + *    task->alloc_lock
>>   *   read_lock css_set_lock (cgroup iterator start)
>> - *    sighand->siglock
>> + *    sighand->siglock (fake signal delivery inside freeze_task())
>>   *
>>   * freezer_write() (unfreeze):
>>   * cgroup_mutex
>>   *  freezer->lock
>> + *   write_lock css_set_lock (cgroup iterator start)
>> + *    task->alloc_lock
>>   *   read_lock css_set_lock (cgroup iterator start)
>> - *    task->alloc_lock (to prevent races with freeze_task())
>> + *    task->alloc_lock (inside thaw_process(), prevents race with refrigerator())
>>   *     sighand->siglock
>>   */
>>  static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss,
>>
> 
> 
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