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

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Message-ID: <ac6b0f63-69f4-4f7f-87d6-319c3027ffff@huawei.com>
Date: Tue, 29 Oct 2024 10:42:54 +0800
From: "Liao, Chang" <liaochang1@...wei.com>
To: Will Deacon <will@...nel.org>
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



在 2024/10/24 22:50, Will Deacon 写道:
> 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.

Will

Thanks for pointing out.

> 
>> 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

-- 
BR
Liao, Chang