Commit cf2592f59c0e8ed4308adbdb2e0a88655379d579

Authored by Frederic Weisbecker
Committed by Ingo Molnar
1 parent 17406b82d6

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>

Showing 1 changed file with 7 additions and 1 deletions Side-by-side Diff

... ... @@ -72,7 +72,13 @@
72 72 {
73 73 unsigned long switch_count = t->nvcsw + t->nivcsw;
74 74  
75   - if (t->flags & PF_FROZEN)
  75 + /*
  76 + * Ensure the task is not frozen.
  77 + * Also, when a freshly created task is scheduled once, changes
  78 + * its state to TASK_UNINTERRUPTIBLE without having ever been
  79 + * switched out once, it musn't be checked.
  80 + */
  81 + if (unlikely(t->flags & PF_FROZEN || !switch_count))
76 82 return;
77 83  
78 84 if (switch_count != t->last_switch_count) {