lkml.org 
[lkml]   [2009]   [Feb]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] softlockup: ensure the task has been switched out once
Frederic Weisbecker (fweisbec@gmail.com) wrote:
> 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>
> ---
> kernel/hung_task.c | 8 +++++++-
> 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) {
> --
> 1.6.1
>
>


Looks good to me. Thanks for fixing this!

Acked-by: Mandeep Singh Baines <msb@google.com>


\
 
 \ /
  Last update: 2009-02-10 19:17    [W:0.049 / U:0.484 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site