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Freezer / cgroup freezer: Update stale locking comments 

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.

Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
This commit is contained in:
Matt Helsley 2010-05-10 23:18:47 +02:00 committed by Rafael J. Wysocki
parent 543f2503a9
commit 8f77578cc2
1 changed files with 13 additions and 8 deletions
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21
kernel/cgroup_freezer.c
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@ -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,