Messages in this thread | | | Date | Fri, 21 Nov 2008 09:38:15 -0800 | Subject | Re: [PATCH] cgroups: fix cgroup_iter_next() bug. | From | Paul Menage <> |
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On Fri, Nov 21, 2008 at 12:49 AM, Lai Jiangshan <laijs@cn.fujitsu.com> wrote: > > we access to res->cgroups without the task_lock(), > so res->cgroups may be changed. it's unreliable, > and "if (l == &res->cgroups->tasks)" may be false forever. > > we don't need add any lock for fixing this bug. we just access to > struct css_set by struct cg_cgroup_link, not by struct task_struct. > > since we hold css_set_lock, struct cg_cgroup_link is reliable. > > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Sounds plausible - you'd need to have thread A have completed the call to find_css_set() and then have the iteration begin in thread B, so it's a pretty tight race. But accessing through the cs_cgroup_link is probably conceptually better anyway, regardless of races.
Thanks.
Reviewed-by: Paul Menage <menage@google.com>
> --- > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index 358e775..ddc10ac 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -1810,6 +1819,7 @@ struct task_struct *cgroup_iter_next(struct cgroup *cgrp, > { > struct task_struct *res; > struct list_head *l = it->task; > + struct cg_cgroup_link *link; > > /* If the iterator cg is NULL, we have no tasks */ > if (!it->cg_link) > @@ -1817,7 +1827,8 @@ struct task_struct *cgroup_iter_next(struct cgroup *cgrp, > res = list_entry(l, struct task_struct, cg_list); > /* Advance iterator to find next entry */ > l = l->next; > - if (l == &res->cgroups->tasks) { > + link = list_entry(it->cg_link, struct cg_cgroup_link, cgrp_link_list); > + if (l == &link->cg->tasks) { > /* We reached the end of this task list - move on to > * the next cg_cgroup_link */ > cgroup_advance_iter(cgrp, it); > > >
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