Re: [PATCH] x86/static_call: Remove text_mutex from __static_call_fixup()

[Borislav Petkov]

Hey,

On Thu, Nov 06, 2025 at 11:53:20AM -0600, David Kaplan wrote:
> __static_call_fixup() is only called from apply_returns() which modifies
> text either on boot when only one CPU is active, or on module load.  In
> both cases, it does not modify live code.  This is why this function passes
> 'true' for the modinit argument to __static_call_transform() which causes
> __static_call_transform() to use text_poke_early().
> 
> text_poke_early() does not require that the text_mutex is held, as this
> function is only used when free of any races with other CPUs.  Therefore
> __static_call_fixup() does not need to take the mutex so remove it.
> 
> Signed-off-by: David Kaplan <david.kaplan@xxxxxxx>
> ---
>  arch/x86/kernel/static_call.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c
> index 378c388d1b31..748fc98d416f 100644
> --- a/arch/x86/kernel/static_call.c
> +++ b/arch/x86/kernel/static_call.c
> @@ -212,10 +212,8 @@ bool __static_call_fixup(void *tramp, u8 op, void *dest)
>  		return false;
>  	}
>  
> -	mutex_lock(&text_mutex);
>  	if (op == RET_INSN_OPCODE || dest == &__x86_return_thunk)
>  		__static_call_transform(tramp, RET, NULL, true);
> -	mutex_unlock(&text_mutex);
>  
>  	return true;
>  }
> 

can you please elaborate here what the actual problem was?

I know it had to do with dynamic mitigations, I guess something about
lockdep complaining... can you paste the splat here?

Thx.

-- 
Regards/Gruss,
    Boris.

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