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SubjectRe: preempt-related hangs
Anton Altaparmakov wrote:
>
> At 02:11 25/03/02, Andrew Morton wrote:
> >Andrew Morton wrote:
> > >
> > > ..
> > > Kernel is 2.5.7, dual PIII. When I enable preempt it
> > > locks during boot.
> >
> >OK, this patch fixed it. I don't know why.
>
> Er, because you disable preemption twice and it never gets enabled again? (-:
>
> You probably meant that to be preemt_enable() at the bottom of the patch...
> That might not solve your problem of course... But with the patch you
> basically have completely disabled preemption, you might as well not
> configure it into the kernel. (-;

Yeah I know. Sheesh. I don't even have time to test the fix
before you're on my act :)

Fixed-up workaround with a little debug check is below.

I think Robert's right - the problem is more likely to lie
with the migration thread handoff thingy.

--- 2.5.7/kernel/sched.c~preempt-lockup Sun Mar 24 18:10:49 2002
+++ 2.5.7-akpm/kernel/sched.c Sun Mar 24 18:25:29 2002
@@ -1561,6 +1561,8 @@ void set_cpus_allowed(task_t *p, unsigne
migration_req_t req;
runqueue_t *rq;

+ preempt_disable();
+
new_mask &= cpu_online_map;
if (!new_mask)
BUG();
@@ -1573,7 +1575,7 @@ void set_cpus_allowed(task_t *p, unsigne
*/
if (new_mask & (1UL << p->thread_info->cpu)) {
task_rq_unlock(rq, &flags);
- return;
+ goto out;
}

init_MUTEX_LOCKED(&req.sem);
@@ -1583,6 +1585,8 @@ void set_cpus_allowed(task_t *p, unsigne
wake_up_process(rq->migration_thread);

down(&req.sem);
+out:
+ preempt_enable();
}

static volatile unsigned long migration_mask;
--- 2.5.7/kernel/exit.c~preempt-lockup Sun Mar 24 18:31:39 2002
+++ 2.5.7-akpm/kernel/exit.c Sun Mar 24 18:37:19 2002
@@ -489,6 +489,14 @@ NORET_TYPE void do_exit(long code)
panic("Attempted to kill the idle task!");
if (tsk->pid == 1)
panic("Attempted to kill init!");
+#ifdef CONFIG_PREEMPT
+ if (preempt_get_count()) {
+ printk(KERN_ERR "task `%s' exits with non-zero "
+ "preempt count: %d\n",
+ current->comm,
+ preempt_get_count());
+ }
+#endif
tsk->flags |= PF_EXITING;
del_timer_sync(&tsk->real_timer);

-
-
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