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    SubjectRe: [PATCH v21 015/100] cgroup freezer: Update stale locking comments
    Date
    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


    > 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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