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

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Message-ID: <CAJF2gTRvSkXD+dmVGfObrKE6ZsJdQdcH1G-hRxmYsMSoMbm8vg@mail.gmail.com>
Date:   Thu, 24 Nov 2022 10:10:30 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Conor Dooley <conor@...nel.org>
Cc:     anup@...infault.org, paul.walmsley@...ive.com, palmer@...belt.com,
        conor.dooley@...rochip.com, heiko@...ech.de, rostedt@...dmis.org,
        mhiramat@...nel.org, jolsa@...hat.com, bp@...e.de,
        jpoimboe@...nel.org, suagrfillet@...il.com, andy.chiu@...ive.com,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 1/5] riscv: ftrace: Fixup panic by disabling preemption

On Thu, Nov 24, 2022 at 4:07 AM Conor Dooley <conor@...nel.org> wrote:
>
> On Wed, Nov 23, 2022 at 10:39:46AM -0500, guoren@...nel.org wrote:
> > From: Andy Chiu <andy.chiu@...ive.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