linux-kernel - Re: [PATCH v2] arm64: Return early when break handler is found on linked-list

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Message-ID: <20241024145028.GA31224@willie-the-truck>
Date: Thu, 24 Oct 2024 15:50:30 +0100
From: Will Deacon <will@...nel.org>
To: Liao Chang <liaochang1@...wei.com>
Cc: mark.rutland@....com, catalin.marinas@....com, oliver.upton@...ux.dev,
	kristina.martsenko@....com, ptosi@...gle.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] arm64: Return early when break handler is found on
 linked-list

On Thu, Oct 24, 2024 at 03:41:20AM +0000, Liao Chang wrote:
> The search for breakpoint handlers iterate through the entire
> linked list. Given that all registered hook has a valid fn field, and no
> registered hooks share the same mask and imm. This commit optimize the
> efficiency slightly by returning early as a matching handler is found.
> 
> v2->v1:
> Remove all WARN_ON(!hook->fn) in v1 as Will suggested.

nit: Changelogs like ^^^ should go after the '---' line, otherwise they
end up in the git history.

> Signed-off-by: Liao Chang <liaochang1@...wei.com>
> ---
>  arch/arm64/kernel/debug-monitors.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
> index c60a4a90c6a5..58f047de3e1c 100644
> --- a/arch/arm64/kernel/debug-monitors.c
> +++ b/arch/arm64/kernel/debug-monitors.c
> @@ -303,7 +303,6 @@ static int call_break_hook(struct pt_regs *regs, unsigned long esr)
>  {
>  	struct break_hook *hook;
>  	struct list_head *list;
> -	int (*fn)(struct pt_regs *regs, unsigned long esr) = NULL;
>  
>  	list = user_mode(regs) ? &user_break_hook : &kernel_break_hook;
>  
> @@ -313,10 +312,10 @@ static int call_break_hook(struct pt_regs *regs, unsigned long esr)
>  	 */
>  	list_for_each_entry_rcu(hook, list, node) {
>  		if ((esr_brk_comment(esr) & ~hook->mask) == hook->imm)
> -			fn = hook->fn;
> +			return hook->fn(regs, esr);
>  	}
>  
> -	return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
> +	return DBG_HOOK_ERROR;
>  }
>  NOKPROBE_SYMBOL(call_break_hook);

Acked-by: Will Deacon <will@...nel.org>

I assume Catalin will pick this one up (but he'll need to tweak the
commit message as per my comment above).

Will