Re: [PATCH V3 1/5] riscv: ftrace: Fixup panic by disabling preemption

Guo Ren
2022-11-24T02:10:57Z

On Thu, Nov 24, 2022 at 4:07 AM Conor Dooley <conor@kernel.org> wrote:
>
> On Wed, Nov 23, 2022 at 10:39:46AM -0500, guoren@kernel.org wrote:
> > From: Andy Chiu <andy.chiu@sifive.com>
> >
> > In RISCV, we must use an AUIPC + JALR pair to encode an immediate,
> > forming a jump that jumps to an address over 4K. This may cause errors
> > if we want to enable kernel preemption and remove dependency from
> > patching code with stop_machine(). For example, if a task was switched
> > out on auipc. And, if we changed the ftrace function before it was
> > switched back, then it would jump to an address that has updated 11:0
> > bits mixing with previous XLEN:12 part.
> >
> > p: patched area performed by dynamic ftrace
> > ftrace_prologue:
> > p| REG_S ra, -SZREG(sp)
> > p| auipc ra, 0x? ------------> preempted
> > ...
> > change ftrace function
> > ...
> > p| jalr -?(ra) <------------- switched back
> > p| REG_L ra, -SZREG(sp)
> > func:
> > xxx
> > ret
> >
> > Fixes: fc76b8b8011 ("riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")
>
> ==========
> verify_fixes - FAILED
>
> Commit: be26b864dac9 ("riscv: ftrace: Fixup panic by disabling preemption")
> Fixes tag: Fixes: fc76b8b8011 ("riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")
> Has these problem(s):
> - Target SHA1 does not exist
>
> This should instead be:
> Fixes: afc76b8b8011 ("riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")
Thank you! Sorry, I missed the first letter :P

>
> Thanks,
> Conor.
>

--
Best Regards
Guo Ren