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SubjectRe: [PATCH] softlockup: remove hung_task_check_count

* Mandeep Singh Baines <msb@google.com> wrote:

> read_lock(&tasklist_lock);
> do_each_thread(g, t) {
> - if (!--max_count)
> - goto unlock;
> + if (!--max_count) {
> + /*
> + * Drop the lock every once in a while and resched if
> + * necessary. Don't want to hold the lock too long.
> + */
> + get_task_struct(t);
> + read_unlock(&tasklist_lock);
> + max_count = HUNG_TASK_CHECK_COUNT;
> + if (need_resched())
> + schedule();
> + read_lock(&tasklist_lock);
> + put_task_struct(t);
> + /*
> + * t was unlinked from tasklist. Can't continue in this
> + * case. Exit and try again next time.
> + */
> + if (t->state == TASK_DEAD)
> + goto unlock;
> + }

firstly, this bit should move into a helper function. Also, why dont you
do the need_resched() check first (it's very lighweight) - and thus only
do the heavy ops (get-task-struct & tasklist_lock unlock) if that is set?

But most importantly, isnt the logic above confused? --max_count will
reach zero exactly once, and then we'll loop for a long time.

Ingo


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