From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 99E2712B73 for ; Wed, 23 Oct 2024 01:52:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.187 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729648354; cv=none; b=Bchb6XIQ8JPiI+W2+A5I2rl7oPB/5F2GqbepIJhdJr7ZKjkE1Nm2M8u0xZ8+MqvhbJtM6CP0FSs7AYH3HKhVyzBPqirAVi6BdoWTNV035g2YuuxRgRI2OiPhIcDiFOK2YvcSP388C2c99+B+z2z/LQDKDBIRtfUHer54h8BKV5A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729648354; c=relaxed/simple; bh=/TBq11UmBlTtoHfO0VMvSxgvrNNC+5R4S8pMRLVVmNw=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=QwYgXcLQN+U6I9N/WHMyDjp0lJhThyov648zhVrQNR4uMxxx9b5Tk6nifTMPiyVO0dndgNgJFMczQAhRXIC9BZXlN9vlVMtKW6VBOwVxeiAtteBt6ht9omMw8Qjr9wF//guKS1pzsUz0ILmcjwLxfYru9HmqYkZ/laP/Jcm5jC4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.187 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.88.105]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4XYBnv378Vz10N3R; Wed, 23 Oct 2024 09:50:27 +0800 (CST) Received: from kwepemd200013.china.huawei.com (unknown [7.221.188.133]) by mail.maildlp.com (Postfix) with ESMTPS id D849B14010D; Wed, 23 Oct 2024 09:52:28 +0800 (CST) Received: from [10.67.110.108] (10.67.110.108) by kwepemd200013.china.huawei.com (7.221.188.133) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1258.34; Wed, 23 Oct 2024 09:52:28 +0800 Message-ID: Date: Wed, 23 Oct 2024 09:52:27 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64: Return early when break handler is found on linked-list To: Mark Rutland , Will Deacon CC: , , , , References: <20240827110046.3209679-1-liaochang1@huawei.com> From: "Liao, Chang" In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemd200013.china.huawei.com (7.221.188.133) Hi, Mark and Will Kindly ping. I'd like to get your input on the next step. Should I send a v2 patch that only removes the WARN_ON() as Will suggested? Or should I push forward the refactoring of calling BRK hook [1]. Thanks. [1] https://lore.kernel.org/all/20240906031930.746118-1-liaochang1@huawei.com/ 在 2024/8/27 20:50, Mark Rutland 写道: > On Tue, Aug 27, 2024 at 11:00:46AM +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. >> >> Signed-off-by: Liao Chang > > This looks fine, though I'd love if we could clean this up to remove the > linked list entirely by separating the user/kernel entrypoints and using > a switch statement to decide the handler based on the immediate. That'd > also remove the need for RCU protection. > > Last I looked that would require some largely mechanical restructuring, > and the only painful bit was the hooks that KGDB uses, since those are > the only ones that actually get unregistered. > > Mark. > >> --- >> arch/arm64/kernel/debug-monitors.c | 7 ++++--- >> 1 file changed, 4 insertions(+), 3 deletions(-) >> >> diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c >> index 024a7b245056..fc998956f44c 100644 >> --- a/arch/arm64/kernel/debug-monitors.c >> +++ b/arch/arm64/kernel/debug-monitors.c >> @@ -281,6 +281,7 @@ static LIST_HEAD(kernel_break_hook); >> >> void register_user_break_hook(struct break_hook *hook) >> { >> + WARN_ON(!hook->fn); >> register_debug_hook(&hook->node, &user_break_hook); >> } >> >> @@ -291,6 +292,7 @@ void unregister_user_break_hook(struct break_hook *hook) >> >> void register_kernel_break_hook(struct break_hook *hook) >> { >> + WARN_ON(!hook->fn); >> register_debug_hook(&hook->node, &kernel_break_hook); >> } >> >> @@ -303,7 +305,6 @@ 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 +314,10 @@ 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); >> >> -- >> 2.34.1 >> >> > -- BR Liao, Chang