Christophe Leroy [off-list ref] writes:

Le 30/11/2023 à 13:50, Michael Ellerman a écrit :

quoted

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.

cheers