[PATCH 1/2] cpukit/aarch64: Keep state across context switch

[Sebastian Huber]

On 26/02/2022 08:03, Kinsey Moore wrote:
> On 2/26/2022 00:53, Sebastian Huber wrote:
>> On 26/02/2022 00:41, Kinsey Moore wrote:
>>> This may also be an issue for ARM, RISC-V and others as it doesn't 
>>> appear that ARM saves CPSR during context switch and I couldn't tell 
>>> that RISC-V does this either, though I'm less familiar with it.
>>
>> This doesn't look like the right way to fix this issue.
>>
>> There is currently the assumption that all processors start 
>> multitasking with a context switch to _Thread_Handler() which sets the 
>> interrupt level. It is possible to construct a scenario in which we 
>> start multitasking with a migration of a thread which already executed 
>> the _Thread_Handler() prologue. This would result in an execution with 
>> disabled interrupts. I think the proper fix for this scenario is to 
>> enable interrupts in _CPU_SMP_Prepare_start_multitasking().
>>
>> Doing a context switch with interrupts disabled is a fatal application 
>> error on all architectures with
>>
>> #define CPU_ENABLE_ROBUST_THREAD_DISPATCH TRUE
>>
>> or enabled SMP support.
>>
> Ok, great. I was wondering if that was the case and this is definitely 
> the kind of feedback I was looking for. I'll adjust the patch set to 
> reflect that. I still wonder if this is an issue on other SMP CPU ports, 
> though, since most of them don't implement that hook, either.

I would like to have a closer look at this next week then I am back from 
holidays.

Enabling interrupts in _CPU_SMP_Prepare_start_multitasking() would not 
work since we use the interrupt stack at this point. We should add a 
ticket and a test case for this (I can do this next week). How did you 
observe this bug?

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