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authorLi Zefan <lizefan@huawei.com>2013-01-24 14:43:28 +0800
committerTejun Heo <tj@kernel.org>2013-02-18 09:08:10 -0800
commit71b5707e119653039e6e95213f00479668c79b75 (patch)
treecb0dfe84c3b8ec46efce2aa4185342a3a75cc3a1 /kernel/cgroup.c
parent9ed8a659703876a9fe96ab86d1b296c2f0084242 (diff)
cgroup: fix exit() vs rmdir() race
In cgroup_exit() put_css_set_taskexit() is called without any lock, which might lead to accessing a freed cgroup: thread1 thread2 --------------------------------------------- exit() cgroup_exit() put_css_set_taskexit() atomic_dec(cgrp->count); rmdir(); /* not safe !! */ check_for_release(cgrp); rcu_read_lock() can be used to make sure the cgroup is alive. Signed-off-by: Li Zefan <lizefan@huawei.com> Signed-off-by: Tejun Heo <tj@kernel.org> Cc: stable@vger.kernel.org
Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r--kernel/cgroup.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 800852282c21..5d4c92ead691 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -422,12 +422,20 @@ static void __put_css_set(struct css_set *cg, int taskexit)
struct cgroup *cgrp = link->cgrp;
list_del(&link->cg_link_list);
list_del(&link->cgrp_link_list);
+
+ /*
+ * We may not be holding cgroup_mutex, and if cgrp->count is
+ * dropped to 0 the cgroup can be destroyed at any time, hence
+ * rcu_read_lock is used to keep it alive.
+ */
+ rcu_read_lock();
if (atomic_dec_and_test(&cgrp->count) &&
notify_on_release(cgrp)) {
if (taskexit)
set_bit(CGRP_RELEASABLE, &cgrp->flags);
check_for_release(cgrp);
}
+ rcu_read_unlock();
kfree(link);
}