BUG: commit "ARM: Remove __ARCH_WANT_INTERRUPTS_ON_CTXSW on pre-ARMv6 CPUs" breaks armv5 with CONFIG_PREEMPT

On Thu, Jun 20, 2013 at 12:47:25PM +0100, Marc Kleine-Budde wrote:

On 06/20/2013 01:39 PM, Marc Kleine-Budde wrote:

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On 06/20/2013 01:35 PM, Marc Kleine-Budde wrote:

quoted

On 06/20/2013 01:12 PM, Catalin Marinas wrote:

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On Thu, Jun 20, 2013 at 11:28:56AM +0100, Catalin Marinas wrote:

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We may need to place the preempt disable/enable at a higher level in the
scheduler. My theory is that we have a context switch from prev to next.
We get preempted just before finish_arch_post_lock_switch(), so the MMU
hasn't been switched yet. The new switch during preemption happens to a
thread with the same next mm, so the scheduler no longer switch_mm() and
the TIF_SWITCH_MM isn't set for the new thread.

I'll come back with another patch shortly.

Here's another attempt (as before, only compile-tested):

booting kernel from /image
zImage: concatenated oftree detected
booting Linux kernel with devicetree

...dead...

Does every process have a "mm"? Even Kernel threads?

I've added a check for "mm". Boots now and my test runs stable for 3
minutes now.

Ah, good point.

I'm not sure if we have to check for "mm" in
check_and_switch_context(), too.

switch_mm() wouldn't be called with a NULL mm, hence we wouldn't call
check_and_switch_context() either. finish_arch_post_lock_switch() is
called all the time (and we set the TIF flag only if switch_mm() was
called).

Thanks.

-- 
Catalin