Re: [Xenomai-help] kernel oopses when killing realtime task

[Jan Kiszka <jan.kiszka@domain.hid>]

Am 07.10.2010 13:57, Pavel Machek wrote:
> Hi!
> 
> I have... quite an interesting setup here.
> 
> SMP machine, with special PCI card; that card has GPIOs and serial
> ports. Unfortunately, there's only one interrupt, shared between
> serials and GPIO pins, and serials are way too complex to be handled
> by realtime layer.
> 
> So I ended up with
> 
>         // we also have an interrupt handler:                                                                                                                 
>         ret = rtdm_irq_request(&my_context->irq_handle,
>         gpio_rt_config.irq, demo_interrupt,
>                                RTDM_IRQTYPE_SHARED,
>         context->device->proc_name, my_context);
> 
> and 
> 
> static int demo_interrupt(rtdm_irq_t *irq_context)
> {
>         struct demodrv_context *ctx;
>         int           dev_id;
>         int           ret = RTDM_IRQ_HANDLED; // usual return value                                                                                           
>         unsigned pending, output;
> 
>         ctx = rtdm_irq_get_arg(irq_context, struct demodrv_context);
>         dev_id    = ctx->dev_id;
> 
>         if (!ctx->ready) {
>                 printk(KERN_CRIT "Unexpected interrupt\n");
>                 return XN_ISR_PROPAGATE;

Who sets ready and when? Looks racy.

>         }               
> 
>         rtdm_lock_get(&ctx->lock);
> 
>         pending = pgread(GPIO_IRQ_ID);
>         pgwrite(0, GPIO_IRQ_ID);
>         output = pgread(GPIO_STATUS_OUT);
>         output ^= (1<<3);
>         pgwrite(output, GPIO_STATUS_OUT);
> 
>         // do stuff                                                                                                                                           
>         if (events > 1000) {
>                 rtdm_event_signal(&ctx->irq_event);
>                 events = 0;
>         }
>         events++;
>         
>         rtdm_lock_put(&ctx->lock);
>  
>         /* We need to propagate the interrupt, so that PMC-6L serials                                                                                         
>            work. Result is that interrupt latencies can't be                                                                                                  
>            guaranteed when serials are in use.  */
> 
>          return RTDM_IRQ_HANDLED;
> }
> 
> Unregistration is:
>         my_context->ready = 0;
>         rtdm_irq_disable(&my_context->irq_handle);

Where is rtdm_irq_free? Again, this ready flag looks racy.

> 
> 
> Unfortunately, when the userspace app is ran and killed repeatedly (so
> that interrupt is registered/unregistered all the time), I get
> oopses in __ipipe_dispatch_wired() -- it seems to call into the NULL
> pointer.
> 
> I decided that "wired" interrupt when the source is shared between
> Linux and Xenomai, is wrong thing, so I disable "wired" interrupts
> altogether, but that only moved oops to __virq_end. 

This is wrong. The only way to get a determistically shared IRQs across
domains is via the wired path, either using the pattern Gilles cited or,
in a slight variation, signaling down via a separate rtdm_nrtsig.

> 
> I'm using 2.6.27.21-ELinOS-46 with xenomai-2.4.7 . Problem does go
> away if I boot with maxcpus=1.
> 
> Any ideas? (Besides using non-historic kernel; but that's
> unfortunately not exactly easy here.)
> 
> 								Pavel

Jan

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