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SubjectRe: [PATCH v21 015/100] cgroup freezer: Update stale locking comments
On Thu, May 06, 2010 at 09:40:19PM +0200, Rafael J. Wysocki wrote:
> On Saturday 01 May 2010, Oren Laadan wrote:
> > From: Matt Helsley <matthltc@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.
>
> I guess these three patches are for me.
>
> Do you want me to handle them?
>
> Rafael

Hi Rafael,

I think you can take 15 as it's an update to the comments.

16 and 17 are specific to checkpoint/restart. There are no other in-kernel
uses, that we've identified, for them. So I was under the impression that it's
inappropriate to add them without also adding the checkpoint/restart patches
that use them.

Thanks!

Cheers,
-Matt Helsley

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


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