[PATCH] powerpc/irq: Allow softirq to hardirq stack transition

[Christophe Leroy]

Le 01/12/2023 à 11:05, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy at csgroup.eu> writes:
>> Le 30/11/2023 à 13:50, Michael Ellerman a écrit :
>>> Allow a transition from the softirq stack to the hardirq stack when
>>> handling a hardirq. Doing so means a hardirq received while deep in
>>> softirq processing is less likely to cause a stack overflow of the
>>> softirq stack.
>>>
>>> Previously it wasn't safe to do so because irq_exit() (which initiates
>>> softirq processing) was called on the hardirq stack.
>>>
>>> That was changed in commit 1b1b6a6f4cc0 ("powerpc: handle irq_enter/
>>> irq_exit in interrupt handler wrappers") and 1346d00e1bdf ("powerpc:
>>> Don't select HAVE_IRQ_EXIT_ON_IRQ_STACK").
>>>
>>> The allowed transitions are now:
>>>    - process stack -> hardirq stack
>>>    - process stack -> softirq stack
>>>    - process stack -> softirq stack -> hardirq stack
>>
>> It means you don't like my patch
>> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/6cd9d8bb2258d8b51999c2584eac74423d2b5e29.1657203774.git.christophe.leroy@csgroup.eu/
>> ?
> 
> I did like your patch :)
> 
> But then we got reports of folks hitting stack overflow in some distro
> kernels, and in at least some cases it was a hardirq coming in during
> softirq handling and overflowing the softirq stack.

Fair enough, I'll discard it.

> 
>> I never got any feedback.
> 
> Sorry, not enough hours in the day.
> 

Yes same problem here :)