[PATCH] softlockup: ensure the task has been scheduled once

[Frederic Weisbecker]

When we check if the task has been scheduled since the last scan, we might
have a race condition if the task has been inserted on the task list but not
yet scheduled once. So we just add a small check to ensure it has been switched
in at least one time to avoid false positive.

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
---
 kernel/hung_task.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 4a10756..7f57a71 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -72,7 +72,11 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
 {
 	unsigned long switch_count = t->nvcsw + t->nivcsw;
 
-	if (t->flags & PF_FROZEN)
+	/*
+	 * Ensure the task is not frozen and that it has been scheduled
+	 * at least once.
+	 */
+	if (t->flags & PF_FROZEN || !switch_count)
 		return;
 
 	if (switch_count != t->last_switch_count) {
-- 
1.6.1

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