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Commit 8f77578c authored by Matt Helsley's avatar Matt Helsley Committed by Rafael J. Wysocki
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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: default avatarMatt Helsley <matthltc@us.ibm.com>
Signed-off-by: default avatarRafael J. Wysocki <rjw@sisk.pl>
parent 543f2503

kernel/cgroup_freezer.c

+13 −8
Original line number Diff line number Diff line
@@ -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,