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>
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@ -89,10 +89,10 @@ struct cgroup_subsys freezer_subsys;
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/* Locks taken and their ordering
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* ------------------------------
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* css_set_lock
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* cgroup_mutex (AKA cgroup_lock)
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* task->alloc_lock (AKA task_lock)
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* freezer->lock
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* css_set_lock
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* task->alloc_lock (AKA task_lock)
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* task->sighand->siglock
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*
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* cgroup code forces css_set_lock to be taken before task->alloc_lock
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@ -100,33 +100,38 @@ struct cgroup_subsys freezer_subsys;
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* freezer_create(), freezer_destroy():
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* cgroup_mutex [ by cgroup core ]
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*
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* can_attach():
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* cgroup_mutex
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* freezer_can_attach():
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* cgroup_mutex (held by caller of can_attach)
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*
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* cgroup_frozen():
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* cgroup_freezing_or_frozen():
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* task->alloc_lock (to get task's cgroup)
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*
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* freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
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* task->alloc_lock (to get task's cgroup)
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* freezer->lock
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* sighand->siglock (if the cgroup is freezing)
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*
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* freezer_read():
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* cgroup_mutex
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* freezer->lock
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* write_lock css_set_lock (cgroup iterator start)
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* task->alloc_lock
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* read_lock css_set_lock (cgroup iterator start)
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*
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* freezer_write() (freeze):
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* cgroup_mutex
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* freezer->lock
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* write_lock css_set_lock (cgroup iterator start)
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* task->alloc_lock
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* read_lock css_set_lock (cgroup iterator start)
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* sighand->siglock
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* sighand->siglock (fake signal delivery inside freeze_task())
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*
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* freezer_write() (unfreeze):
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* cgroup_mutex
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* freezer->lock
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* write_lock css_set_lock (cgroup iterator start)
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* task->alloc_lock
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* read_lock css_set_lock (cgroup iterator start)
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* task->alloc_lock (to prevent races with freeze_task())
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* task->alloc_lock (inside thaw_process(), prevents race with refrigerator())
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* sighand->siglock
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*/
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static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss,
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