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

Michael Ellerman mpe at ellerman.id.au
Fri Dec 1 21:05:27 AEDT 2023

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.

> I never got any feedback.

Sorry, not enough hours in the day.


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