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SubjectRe: status of: tasklet_unlock_wait() causes soft lockup with -rt and ieee1394 audio
Ingo Molnar wrote:
> * Pieter Palmers <pieterp@joow.be> wrote:
>
>> Dear all,
>>
>> What is the status with respect to this problem? I see that in the
>> current -rt patch the problematic code piece is different. I
>> personally haven't tried to reproduce this myself on a more recent
>> kernel, but I just got a report from one of our users who experienced
>> the same problem with 2.6.19-rt15 and RT preemption (desktop
>> preemption works fine).
>>
>> Should the latest -rt patches be fixed with respect to this issue? If
>> so I'll try and test them, otherwise I omit the effort.
>
> it's not fixed yet. Could you try the patch below?

Ingo,

I couldn't get my laptop booting on 2.6.20-rc3 or 2.6.19, but I passed
the patch on to one of our users and he reports that it is working (on
2.6.19-rt15).

Thanks,

Pieter

>
> Ingo
>
> ---
> include/linux/interrupt.h | 6 ++----
> kernel/softirq.c | 20 ++++++++++++++++++++
> 2 files changed, 22 insertions(+), 4 deletions(-)
>
> Index: linux/include/linux/interrupt.h
> ===================================================================
> --- linux.orig/include/linux/interrupt.h
> +++ linux/include/linux/interrupt.h
> @@ -328,10 +328,8 @@ static inline void tasklet_unlock(struct
> clear_bit(TASKLET_STATE_RUN, &(t)->state);
> }
>
> -static inline void tasklet_unlock_wait(struct tasklet_struct *t)
> -{
> - while (test_bit(TASKLET_STATE_RUN, &(t)->state)) { barrier(); }
> -}
> +extern void tasklet_unlock_wait(struct tasklet_struct *t);
> +
> #else
> # define tasklet_trylock(t) 1
> # define tasklet_tryunlock(t) 1
> Index: linux/kernel/softirq.c
> ===================================================================
> --- linux.orig/kernel/softirq.c
> +++ linux/kernel/softirq.c
> @@ -20,6 +20,7 @@
> #include <linux/mm.h>
> #include <linux/notifier.h>
> #include <linux/percpu.h>
> +#include <linux/delay.h>
> #include <linux/cpu.h>
> #include <linux/kthread.h>
> #include <linux/rcupdate.h>
> @@ -656,6 +657,25 @@ void __init softirq_init(void)
> open_softirq(HI_SOFTIRQ, tasklet_hi_action, NULL);
> }
>
> +#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
> +
> +void tasklet_unlock_wait(struct tasklet_struct *t)
> +{
> + while (test_bit(TASKLET_STATE_RUN, &(t)->state)) {
> + /*
> + * Hack for now to avoid this busy-loop:
> + */
> +#ifdef CONFIG_PREEMPT_RT
> + msleep(1);
> +#else
> + barrier();
> +#endif
> + }
> +}
> +EXPORT_SYMBOL(tasklet_unlock_wait);
> +
> +#endif
> +
> static int ksoftirqd(void * __data)
> {
> struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO/2 };
>

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