[PATCH] cpuset: Add missing rcu read locks

[PATCH] cpuset: Add missing rcu read locks

[Sasha Levin]

We call task_cs() which ends up going into cgroup code without having rcu
read lock. Fix it by grabbing the lock before retrival of task_cs() and usage
of the result.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---
 kernel/cpuset.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index be9c1da..64bd8a4 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2240,8 +2240,10 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
 
 	mutex_lock(&callback_mutex);
 	task_lock(tsk);
+	rcu_read_lock();
 	cpus_cs = effective_cpumask_cpuset(task_cs(tsk));
 	guarantee_online_cpus(cpus_cs, pmask);
+	rcu_read_unlock();
 	task_unlock(tsk);
 	mutex_unlock(&callback_mutex);
 }
@@ -2296,8 +2298,10 @@ nodemask_t cpuset_mems_allowed(struct task_struct *tsk)
 
 	mutex_lock(&callback_mutex);
 	task_lock(tsk);
+	rcu_read_lock();
 	mems_cs = effective_nodemask_cpuset(task_cs(tsk));
 	guarantee_online_mems(mems_cs, &mask);
+	rcu_read_unlock();
 	task_unlock(tsk);
 	mutex_unlock(&callback_mutex);
 
-- 
1.7.2.5

Re: [PATCH] cpuset: Add missing rcu read locks

[Li Zefan]

On 2014/2/27 22:20, Sasha Levin wrote:
> We call task_cs() which ends up going into cgroup code without having rcu
> read lock. Fix it by grabbing the lock before retrival of task_cs() and usage
> of the result.
> 

Thanks for the patch.

Fengguang already reported it, and I've made a patch for it, but I was fixing
two bugs for 3.14 and then waiting for them to be applied.

There're other places that rcu_read_lock() should be used, and we need to
remove task_lock().