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authorFrederic Weisbecker <fweisbec@gmail.com>2009-02-10 15:52:37 (GMT)
committerIngo Molnar <mingo@elte.hu>2009-02-11 10:04:16 (GMT)
commitcf2592f59c0e8ed4308adbdb2e0a88655379d579 (patch)
tree383b30bc13af8ce83e15825b041d8bb791ea4cea /kernel/hung_task.c
parent17406b82d621930cca8ccc1272cdac9a7dae8e40 (diff)
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softlockup: ensure the task has been switched out once
When we check if a task has been switched out since the last scan, we might have a race condition on the following scenario: - the task is freshly created and scheduled - it puts its state to TASK_UNINTERRUPTIBLE and is not yet switched out - check_hung_task() scans this task and will report a false positive because t->nvcsw + t->nivcsw == t->last_switch_count == 0 Add a check for such cases. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Acked-by: Mandeep Singh Baines <msb@google.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/hung_task.c')
-rw-r--r--kernel/hung_task.c8
1 files changed, 7 insertions, 1 deletions
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 0c924de..022a492 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -72,7 +72,13 @@ 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.
+ * Also, when a freshly created task is scheduled once, changes
+ * its state to TASK_UNINTERRUPTIBLE without having ever been
+ * switched out once, it musn't be checked.
+ */
+ if (unlikely(t->flags & PF_FROZEN || !switch_count))
return;
if (switch_count != t->last_switch_count) {