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sched: Fix an RCU warning in print_task()

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With CONFIG_PROVE_RCU=y, a warning can be triggered:

  $ cat /proc/sched_debug

...
kernel/cgroup.c:1649 invoked rcu_dereference_check() without protection!
...

Both cgroup_path() and task_group() should be called with either
rcu_read_lock or cgroup_mutex held.

The rcu_dereference_check() does include cgroup_lock_is_held(), so we
know that this lock is not held.  Therefore, in a CONFIG_PREEMPT kernel,
to say nothing of a CONFIG_PREEMPT_RT kernel, the original code could
have ended up copying a string out of the freelist.

This patch inserts RCU read-side primitives needed to prevent this
scenario.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Li Zefan 2010-04-22 17:30:40 +08:00 committed by Paul E. McKenney
parent fae9c79170
commit b629317e66
1 changed files with 2 additions and 0 deletions
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kernel/sched_debug.c
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@ -114,7 +114,9 @@ print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
{
char path[64];
rcu_read_lock();
cgroup_path(task_group(p)->css.cgroup, path, sizeof(path));
rcu_read_unlock();
SEQ_printf(m, " %s", path);
}
#endif