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SubjectRe: [PATCH 2/2 v4] softlockup: check all tasks in hung_task
On Thu, 5 Feb 2009 15:34:53 +0100 Ingo Molnar <mingo@elte.hu> wrote:

>
> Subject: [PATCH] softlockup: check all tasks in hung_task
>
> Impact: extend the scope of hung-task checks
>

A nanonit:

> +static const int hung_task_batching = 1024;

static const definitions look pretty but they're a bit misleading.

> static void check_hung_uninterruptible_tasks(unsigned long timeout)
> {
> + int batch_count = hung_task_batching;
> int max_count = sysctl_hung_task_check_count;
> unsigned long now = get_timestamp();
> struct task_struct *g, *t;
> @@ -131,6 +159,13 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
> do_each_thread(g, t) {
> if (!--max_count)
> goto unlock;
> + if (!--batch_count) {
> + batch_count = hung_task_batching;
> + rcu_lock_break(g, t);
> + /* Exit if t or g was unhashed during refresh. */
> + if (t->state == TASK_DEAD || g->state == TASK_DEAD)
> + goto unlock;
> + }
> /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
> if (t->state == TASK_UNINTERRUPTIBLE)
> check_hung_task(t, now, timeout);

The reader of this area of the code will expect that hung_task_batching
is a variable. It _looks_ like the value of that variable can be altered
at any time by some other thread. It _looks_ like this code will explode
if someone has accidentally set hung_task_batching to zero, etc.

But none of that is actually true, because hung_task_batching is, surprisingly,
a compile-time constant.

All this misleadingness would be fixed if it were called
HUNG_TASK_BATCHING. But then it wouldn't be pretty.



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