From e0197aae59e55c06db172bfbe1a1cdb8c0e1cab3 Mon Sep 17 00:00:00 2001 From: Mandeep Singh Baines Date: Thu, 15 Dec 2011 11:36:43 -0800 Subject: [PATCH] cgroups: fix a css_set not found bug in cgroup_attach_proc There is a BUG when migrating a PF_EXITING proc. Since css_set_prefetch() is not called for the PF_EXITING case, find_existing_css_set() will return NULL inside cgroup_task_migrate() causing a BUG. This bug is easy to reproduce. Create a zombie and echo its pid to cgroup.procs. $ cat zombie.c \#include int main() { if (fork()) pause(); return 0; } $ We are hitting this bug pretty regularly on ChromeOS. This bug is already fixed by Tejun Heo's cgroup patchset which is targetted for the next merge window: https://lkml.org/lkml/2011/11/1/356 I've create a smaller patch here which just fixes this bug so that a fix can be merged into the current release and stable. Signed-off-by: Mandeep Singh Baines Downstream-Bug-Report: http://crosbug.com/23953 Reviewed-by: Li Zefan Signed-off-by: Tejun Heo Cc: containers@lists.linux-foundation.org Cc: cgroups@vger.kernel.org Cc: stable@kernel.org Cc: KAMEZAWA Hiroyuki Cc: Frederic Weisbecker Cc: Oleg Nesterov Cc: Andrew Morton Cc: Paul Menage Cc: Olof Johansson --- kernel/cgroup.c | 5 ----- 1 file changed, 5 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index d9d5648f3cdc..a184470cf9b5 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2098,11 +2098,6 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) continue; /* get old css_set pointer */ task_lock(tsk); - if (tsk->flags & PF_EXITING) { - /* ignore this task if it's going away */ - task_unlock(tsk); - continue; - } oldcg = tsk->cgroups; get_css_set(oldcg); task_unlock(tsk);