Re: [PATCH 6.1 v1] RISC-V: fix lock splat in riscv_cpufeature_patch_func()

[Conor Dooley <conor.dooley@microchip.com>]

[-- Attachment #1: Type: text/plain, Size: 1409 bytes --]

On Thu, May 11, 2023 at 07:39:25PM -0400, Sasha Levin wrote:
> On Tue, May 09, 2023 at 10:36:42PM +0100, Conor Dooley wrote:
> > From: Conor Dooley <conor.dooley@microchip.com>
> > 
> > Guenter reported a lockdep splat that appears to have been present for a
> > while in v6.1.y & the backports of the riscv_patch_in_stop_machine dance
> > did nothing to help here, as the lock is not being taken when
> > patch_text_nosync() is called in riscv_cpufeature_patch_func().
> > Add the lock/unlock; elide the splat.
> 
> Is this not a problem upstream?

It is not. Nor is it a problem in 6.2 either.
In fact, looking at it at a time other than 22h30, I notice that this is
not a complete patch. Instead we need to backport commit 9493e6f3ce02
("RISC-V: take text_mutex during alternative patching") and bf89b7ee52af
("RISC-V: fix taking the text_mutex twice during sifive errata patching")
to 6.1. The automagic version failed:
https://lore.kernel.org/stable/a2a21e9c-41ec-46dd-b792-6314c5fa4241@spud/

And I was of the opinion that this was not needed for kernels without
commit 702e64550b12 ("riscv: fpu: switch has_fpu() to
riscv_has_extension_likely()").

I'll go send those now, I am surprised noone has complained about the
SiFive errata causing a splat, but I guess noone with that hardware is
testing stable. The T-HEAD errata has no functional users in 6.1.

Thanks,
Conor.

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]