| From | Ben Hutchings <> | Date | Mon, 31 Mar 2014 00:23:35 +0100 | Subject | [PATCH 3.2 129/200] cgroup: update cgroup_enable_task_cg_lists() to grab siglock |
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3.2.56-rc1 review patch. If anyone has any objections, please let me know.
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From: Tejun Heo <tj@kernel.org>
commit 532de3fc72adc2a6525c4d53c07bf81e1732083d upstream.
Currently, there's nothing preventing cgroup_enable_task_cg_lists() from missing set PF_EXITING and race against cgroup_exit(). Depending on the timing, cgroup_exit() may finish with the task still linked on css_set leading to list corruption. Fix it by grabbing siglock in cgroup_enable_task_cg_lists() so that PF_EXITING is guaranteed to be visible.
This whole on-demand cg_list optimization is extremely fragile and has ample possibility to lead to bugs which can cause things like once-a-year oops during boot. I'm wondering whether the better approach would be just adding "cgroup_disable=all" handling which disables the whole cgroup rather than tempting fate with this on-demand craziness.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com> [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- kernel/cgroup.c | 5 +++++ 1 file changed, 5 insertions(+)
--- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2785,9 +2785,14 @@ static void cgroup_enable_task_cg_lists( * We should check if the process is exiting, otherwise * it will race with cgroup_exit() in that the list * entry won't be deleted though the process has exited. + * Do it while holding siglock so that we don't end up + * racing against cgroup_exit(). */ + spin_lock_irq(&p->sighand->siglock); if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list)) list_add(&p->cg_list, &p->cgroups->tasks); + spin_unlock_irq(&p->sighand->siglock); + task_unlock(p); } while_each_thread(g, p); write_unlock(&css_set_lock);
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