Commit b629317e authored by Li Zefan's avatar Li Zefan Committed by Paul E. McKenney

sched: Fix an RCU warning in print_task()

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: default avatarLi Zefan <lizf@cn.fujitsu.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent fae9c791
...@@ -114,7 +114,9 @@ print_task(struct seq_file *m, struct rq *rq, struct task_struct *p) ...@@ -114,7 +114,9 @@ print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
{ {
char path[64]; char path[64];
rcu_read_lock();
cgroup_path(task_group(p)->css.cgroup, path, sizeof(path)); cgroup_path(task_group(p)->css.cgroup, path, sizeof(path));
rcu_read_unlock();
SEQ_printf(m, " %s", path); SEQ_printf(m, " %s", path);
} }
#endif #endif
......
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