linux-kernel - Re: [PATCH v2] powerpc: Fix save_stack_trace_regs() to have running function as first entry

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Date:   Thu, 04 Mar 2021 22:36:49 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>, elver@...gle.com,
        rostedt@...dmis.org
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kasan-dev@...glegroups.com,
        Segher Boessenkool <segher@...nel.crashing.org>
Subject: Re: [PATCH v2] powerpc: Fix save_stack_trace_regs() to have running
 function as first entry

Christophe Leroy <christophe.leroy@...roup.eu> writes:
> It seems like other architectures, namely x86 and arm64
> at least, include the running function as top entry when saving
> stack trace with save_stack_trace_regs().

Also riscv AFAICS.

> Functionnalities like KFENCE expect it.
>
> Do the same on powerpc, it allows KFENCE to properly identify the faulting
> function as depicted below. Before the patch KFENCE was identifying
> finish_task_switch.isra as the faulting function.

Thanks, I think this is the right approach. There's kfence but also
several other users from what I can see with a quick grep.

...
>
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> Fixes: 35de3b1aa168 ("powerpc: Implement save_stack_trace_regs() to enable kprobe stack tracing")
> Cc: stable@...r.kernel.org

I'm not sure about the Cc to stable. I think we are fixing the behaviour
to match the (implied) intent of the API, but that doesn't mean we won't
break something by accident. I'll think about it :)

cheers