On Fri, Mar 09, 2012 at 01:20:16PM +0900, KAMEZAWA Hiroyuki wrote:
> On Fri, 09 Mar 2012 12:07:32 +0800
> Sha Zhengju <handai.szj@xxxxxxxxx> wrote:
>
> > On 03/09/2012 11:40 AM, KAMEZAWA Hiroyuki wrote:
> > > On Tue, 6 Mar 2012 20:13:24 +0800
> > > Sha Zhengju<handai.szj@xxxxxxxxx> wrote:
> > >
> > >> From: Sha Zhengju<handai.szj@xxxxxxxxxx>
> > >>
> > >> When the last event is unregistered, there is no need to keep the spare
> > >> array anymore. So free it to avoid memory leak.
> > >>
> > >> Signed-off-by: Sha Zhengju<handai.szj@xxxxxxxxxx>
> > >>
> > >> ---
> > >> mm/memcontrol.c | 6 ++++++
> > >> 1 files changed, 6 insertions(+), 0 deletions(-)
> > >>
> > >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > >> index 22d94f5..3c09a84 100644
> > >> --- a/mm/memcontrol.c
> > >> +++ b/mm/memcontrol.c
> > >> @@ -4412,6 +4412,12 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
> > >> swap_buffers:
> > >> /* Swap primary and spare array */
> > >> thresholds->spare = thresholds->primary;
> > >> + /* If all events are unregistered, free the spare array */
> > >> + if (!new) {
> > >> + kfree(thresholds->spare);
> > >> + thresholds->spare = NULL;
> > >> + }
> > >> +
> > > Could you clear thresholds->primary ? I don't like a pointer points to freed memory.
> > Do you meaning I should set ‘thresholds->primary = NULL‘ ？
> > But the following rcu_assign_pointer will do this :
> >
> > + /* If all events are unregistered, free the spare array */
> > + if (!new) {
> > + kfree(thresholds->spare);
> > + thresholds->spare = NULL;
> > + }
> > +
> > rcu_assign_pointer(thresholds->primary, new);<---------*HERE*
> >
>
> Hm, ok.
>
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
>
> BTW, can memory cgroup be destroyed while there are registered events ?
Yes, it can. All eventfds will be closed first. See cgroup_rmdir().
And here's possibility of leak. If we have an eventfd with >1 threasholds
attached to it, mem_cgroup_usage_unregister_event() will leave spare
not freed. And then we destroy cgroup...
Reviewed-by: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
--
Kirill A. Shutemov
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