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From: Oren Laadan on 1 May 2010 10:30
From: Matt Helsley <matthltc(a)us.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.

Signed-off-by: Matt Helsley <matthltc(a)us.ibm.com>
Cc: Oren Laadan <orenl(a)cs.columbia.edu>
Cc: Cedric Le Goater <legoater(a)free.fr>
Cc: Paul Menage <menage(a)google.com>
Cc: Li Zefan <lizf(a)cn.fujitsu.com>
Cc: Rafael J. Wysocki <rjw(a)sisk.pl>
Cc: linux-pm(a)lists.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,
--
1.6.3.3

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Prev: [PATCH 1/3] input: mt: Simplify event bypass logic
Next: [PATCH v21 019/100] Make file_pos_read/write() public and export kernel_write()