sched: partly revert "sched debug: remove NULL checking in print_cfs_rt_rq()"
Impact: avoid accessing NULL tg.css->cgroup
In commit 0a0db8f5c9d4bbb9bbfcc2b6cb6bce2d0ef4d73d, I removed checking
NULL tg.css->cgroup, but I realized I was wrong when I found reading
/proc/sched_debug can race with cgroup_create().
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index 4293cfa..16eeba4e 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -145,6 +145,19 @@
read_unlock_irqrestore(&tasklist_lock, flags);
}
+#if defined(CONFIG_CGROUP_SCHED) && \
+ (defined(CONFIG_FAIR_GROUP_SCHED) || defined(CONFIG_RT_GROUP_SCHED))
+static void task_group_path(struct task_group *tg, char *buf, int buflen)
+{
+ /* may be NULL if the underlying cgroup isn't fully-created yet */
+ if (!tg->css.cgroup) {
+ buf[0] = '\0';
+ return;
+ }
+ cgroup_path(tg->css.cgroup, buf, buflen);
+}
+#endif
+
void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
{
s64 MIN_vruntime = -1, min_vruntime, max_vruntime = -1,
@@ -154,10 +167,10 @@
unsigned long flags;
#if defined(CONFIG_CGROUP_SCHED) && defined(CONFIG_FAIR_GROUP_SCHED)
- char path[128] = "";
+ char path[128];
struct task_group *tg = cfs_rq->tg;
- cgroup_path(tg->css.cgroup, path, sizeof(path));
+ task_group_path(tg, path, sizeof(path));
SEQ_printf(m, "\ncfs_rq[%d]:%s\n", cpu, path);
#elif defined(CONFIG_USER_SCHED) && defined(CONFIG_FAIR_GROUP_SCHED)
@@ -208,10 +221,10 @@
void print_rt_rq(struct seq_file *m, int cpu, struct rt_rq *rt_rq)
{
#if defined(CONFIG_CGROUP_SCHED) && defined(CONFIG_RT_GROUP_SCHED)
- char path[128] = "";
+ char path[128];
struct task_group *tg = rt_rq->tg;
- cgroup_path(tg->css.cgroup, path, sizeof(path));
+ task_group_path(tg, path, sizeof(path));
SEQ_printf(m, "\nrt_rq[%d]:%s\n", cpu, path);
#else