Re: Searching a Bug on Raspberry Pi

[Kirill Tkhai <tkhai@yandex.ru>]

Hi, Georg!

29.06.2013, 22:39, "Georg Gast" <georg@schorsch-tech.de>:
> Hi there!
>
> Currently i try to locate a bug in sdhci.c on RaspberryPi. I know it is
> not the mainline kernel...
>
> Currently i use Kernel 3.8.13 and RT Patch 3.8.13-rt12 on the kernel
> found at git://github.com/raspberrypi/linux.git on branch rpi-3.8.y.
>
> The bug shows up as booting and after 3 seconds of booting as it wants
> to mount the rootfs in a deadlock. as i compiled sdhci_bcm2708 as a
> module i can boot the kernel and system as i pushed the system to a usb
> stick. As far as good.
>
> Now i try to find the bug, if the rootfs is on the sdcard. I narrowd the
> deadlock down to the following lines:
>
> void sdhci_spin_lock_irqsave(struct sdhci_host *host,unsigned long *flags)
> {
>      return;
> #ifdef CONFIG_PREEMPT
>      if(enable_llm)
>      {
>          while(sdhci_locked)
>          {
>              preempt_schedule();
>          }
>          spin_lock_irqsave(&host->lock,*flags);
>          disable_irq(host->irq);
>          if(host->second_irq)
>              disable_irq(host->second_irq);
>          local_irq_enable();
>      }
>      else
> #endif
>          spin_lock_irqsave(&host->lock,*flags);
> }
>
> void sdhci_spin_unlock_irqrestore(struct sdhci_host *host,unsigned long
> flags)
> {
>      return;
> #ifdef CONFIG_PREEMPT
>      if(enable_llm)
>      {
>          local_irq_disable();
>          if(host->second_irq)
>              enable_irq(host->second_irq);
>          enable_irq(host->irq);
>      }
> #endif
>      spin_unlock_irqrestore(&host->lock,flags);
> }
>
> in drivers/mmc/host/sdhci.c . The both return statements are added by
> me. Now i can boot the RT Preempt kernel but it is for sure not the
> right fix.
>
> My problem is, that i dont know how those both functions should work
> with the rt preempt patch.

Spinlocks transform to mutexes on RT kernel and really functions like
spin_lock_irqsave() do not disable interrupts. Your problem can be connected
with that.

If you code works on !RT kernel you should convert the type of host->lock
from spinlock_t to raw_spinlock_t and all of spin_lock_irqsave()
to raw_spin_lock_irqsave() etc.

I think this will help you. Sadly, I don't have enough time to look at whole of your
driver.

Kirill
--
To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html