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

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Date:   Wed, 23 Nov 2022 20:07:20 +0000
From:   Conor Dooley <conor@...nel.org>
To:     guoren@...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 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")

Thanks,
Conor.