From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga05-in.huawei.com (szxga05-in.huawei.com [45.249.212.191]) (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 F1D9A1CDA2B for ; Tue, 3 Sep 2024 07:00:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.191 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725346817; cv=none; b=Bol7C+p2WLkT7I/9RQqIhFHDIgci2VmTqDyttHWRArTh3EFFHJIlAjpggEv+cQNM20dGOWpEjukSmabD2O9pPFM+nB5y6RLkjrhuRtrPJW+BdKquc+1ibxKG1rnXXF3Za9sAzvpMPyZ8fgMr7+LI9yYwAjRqqdo8zGDbwR10FnY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725346817; c=relaxed/simple; bh=7a/u+B9nl0cQBbB+Sepv2hUi7VRZVW3lGP5tTRZepzs=; h=Subject:From:To:References:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=n3G6Ivlkp/kLz+KYxhm1ooz21hvsDHWPNx0KG/2lEARSDwcSDnZ904SuNCrNpIm//KLGoLwNZY9r/4LXCY9Gj9Z2VsAoYkjypcHtfGQZJm4x90B4R3Ec1bz3xcvM8QSZr3cQp+aS2KQAsQ6+Oxb5Q2x11MH8xVIE7CsgpPC7zsw= 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=45.249.212.191 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 [172.19.88.163]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4WybyP6LLlz1HJ3S; Tue, 3 Sep 2024 14:56:45 +0800 (CST) Received: from dggpemf100006.china.huawei.com (unknown [7.185.36.228]) by mail.maildlp.com (Postfix) with ESMTPS id 1CE7C180019; Tue, 3 Sep 2024 15:00:12 +0800 (CST) Received: from [10.174.178.55] (10.174.178.55) by dggpemf100006.china.huawei.com (7.185.36.228) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 3 Sep 2024 15:00:11 +0800 Subject: Re: [PATCH 1/5] debugobjects: Fix the misuse of global variables in fill_pool() From: "Leizhen (ThunderTown)" To: Thomas Gleixner , Andrew Morton , References: <20240902140532.2028-1-thunder.leizhen@huawei.com> <20240902140532.2028-2-thunder.leizhen@huawei.com> <87mskq58l5.ffs@tglx> <13d2be50-4a52-7cf0-8325-65435ad47a62@huawei.com> <3bb35c94-dd54-33d4-b7ac-64f0d2b77c07@huawei.com> Message-ID: <659f0321-e567-ad48-4545-4a47a158d6c2@huawei.com> Date: Tue, 3 Sep 2024 15:00:11 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <3bb35c94-dd54-33d4-b7ac-64f0d2b77c07@huawei.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemf100006.china.huawei.com (7.185.36.228) On 2024/9/3 11:22, Leizhen (ThunderTown) wrote: > > > On 2024/9/3 10:16, Leizhen (ThunderTown) wrote: >> >> >> On 2024/9/3 0:22, Thomas Gleixner wrote: >>> On Mon, Sep 02 2024 at 22:05, Zhen Lei wrote: >>> >>>> The global variable 'obj_pool_min_free' records the lowest historical >>>> value of the number of nodes in the global list 'obj_pool', instead of >>>> being used as the lowest threshold value. This may be a mistake and >>> >>> Maybe? It's either a bug or not. >> >> Yes, it's a bug, but I'm just learning this module, so I'm not confident. >> >>> >>>> should be replaced with variable 'debug_objects_pool_min_level'. >>> >>> And if it's a bug then it has to be replaced. >> >> OK, I will update the commit message in V2. >> >>> >>> This misses another minor issue: >>> >>> static int obj_pool_min_free = ODEBUG_POOL_SIZE; >>> >>> static int __data_racy debug_objects_pool_min_level __read_mostly >>> = ODEBUG_POOL_MIN_LEVEL; >>> >>> As debug_objects_pool_min_level is the minimum level to keep around and >>> obj_pool_min_free is a statistics mechanism, __data_racy is misplaced >>> too. The variables should swap their position, because >>> debug_objects_pool_min_level is functional, but obj_pool_min_free is >>> pure stats. > > This principle covers a large number of variables. It should be sorted > by the variable name before. It's better not to change the position this time. > >>> >>> Also debug_objects_pool_min_level and debug_objects_pool_size should >>> be __ro_after_init. >> >> OK, How about modifying it like this? I further removed the __data_racy from >> debug_objects_pool_min_level and debug_objects_pool_size, because __ro_after_init. >> >> >> diff --git a/lib/debugobjects.c b/lib/debugobjects.c >> index d3845705db955fa..816d3d968cd9f14 100644 >> --- a/lib/debugobjects.c >> +++ b/lib/debugobjects.c >> @@ -70,7 +70,8 @@ static HLIST_HEAD(obj_to_free); >> * made at debug_stats_show(). Both obj_pool_min_free and obj_pool_max_used >> * can be off. >> */ >> -static int obj_pool_min_free = ODEBUG_POOL_SIZE; >> +static int __ro_after_init debug_objects_pool_size = ODEBUG_POOL_SIZE; >> +static int __ro_after_init debug_objects_pool_min_level = ODEBUG_POOL_MIN_LEVEL; >> static int obj_pool_free = ODEBUG_POOL_SIZE; >> static int obj_pool_used; >> static int obj_pool_max_used; >> @@ -84,10 +85,7 @@ static int __data_racy debug_objects_fixups __read_mostly; >> static int __data_racy debug_objects_warnings __read_mostly; >> static int __data_racy debug_objects_enabled __read_mostly >> = CONFIG_DEBUG_OBJECTS_ENABLE_DEFAULT; >> -static int __data_racy debug_objects_pool_size __read_mostly >> - = ODEBUG_POOL_SIZE; >> -static int __data_racy debug_objects_pool_min_level __read_mostly >> - = ODEBUG_POOL_MIN_LEVEL; >> +static int __data_racy obj_pool_min_free = ODEBUG_POOL_SIZE; Sorry, I rechecked it again. After this patch, obj_pool_min_free is referenced in the same way as obj_pool_max_used. The only race point is located in debug_stats_show(). However, this reference point does not need to be included in the race analysis. So there is no need to add __data_racy for obj_pool_min_free. The final modification is as follows: diff --git a/lib/debugobjects.c b/lib/debugobjects.c index d3845705db955fa..721e207f85b6be7 100644 --- a/lib/debugobjects.c +++ b/lib/debugobjects.c @@ -84,9 +84,9 @@ static int __data_racy debug_objects_fixups __read_mostly; static int __data_racy debug_objects_warnings __read_mostly; static int __data_racy debug_objects_enabled __read_mostly = CONFIG_DEBUG_OBJECTS_ENABLE_DEFAULT; -static int __data_racy debug_objects_pool_size __read_mostly +static int debug_objects_pool_size __ro_after_init = ODEBUG_POOL_SIZE; -static int __data_racy debug_objects_pool_min_level __read_mostly +static int debug_objects_pool_min_level __ro_after_init = ODEBUG_POOL_MIN_LEVEL; static const struct debug_obj_descr *descr_test __read_mostly; >> >> static const struct debug_obj_descr *descr_test __read_mostly; >> static struct kmem_cache *obj_cache __ro_after_init; >> >> >>> >>>> Fixes: d26bf5056fc0 ("debugobjects: Reduce number of pool_lock acquisitions in fill_pool()") >>>> Fixes: 36c4ead6f6df ("debugobjects: Add global free list and the counter") >>> >>> Nice detective work! >>> >>> Thanks, >>> >>> tglx >>> . >>> >> > -- Regards, Zhen Lei