From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2241FC433EF for ; Tue, 2 Nov 2021 13:53:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 09C5D60EDF for ; Tue, 2 Nov 2021 13:53:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231265AbhKBN4a (ORCPT ); Tue, 2 Nov 2021 09:56:30 -0400 Received: from szxga01-in.huawei.com ([45.249.212.187]:30904 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229712AbhKBN42 (ORCPT ); Tue, 2 Nov 2021 09:56:28 -0400 Received: from dggemv704-chm.china.huawei.com (unknown [172.30.72.53]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4HkB8M0BJkzcb3h; Tue, 2 Nov 2021 21:49:07 +0800 (CST) Received: from dggpeml500006.china.huawei.com (7.185.36.76) by dggemv704-chm.china.huawei.com (10.3.19.47) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.15; Tue, 2 Nov 2021 21:53:50 +0800 Received: from [10.174.177.232] (10.174.177.232) by dggpeml500006.china.huawei.com (7.185.36.76) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.15; Tue, 2 Nov 2021 21:53:49 +0800 Subject: Re: [PATCH v2] mm, slub: emit the "free" trace report before freeing memory in kmem_cache_free() To: Yunfeng Ye , , , , , Andrew Morton , , , CC: , , , , Hewenliang References: From: Tang Yizhou Message-ID: Date: Tue, 2 Nov 2021 21:53:49 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.232] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To dggpeml500006.china.huawei.com (7.185.36.76) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/11/2 19:43, Yunfeng Ye wrote: > After the memory is freed, it can be immediately allocated by other > CPUs, before the "free" trace report has been emitted. This causes > inaccurate traces. > > For example, if the following sequence of events occurs: > > CPU 0 CPU 1 > > (1) alloc xxxxxx > (2) free xxxxxx > (3) alloc xxxxxx > (4) free xxxxxx > > Then they will be inaccurately reported via tracing, so that they appear > to have happened in this order: > > CPU 0 CPU 1 > > (1) alloc xxxxxx > (2) alloc xxxxxx > (3) free xxxxxx > (4) free xxxxxx > > This makes it look like CPU 1 somehow managed to allocate mmemory that > CPU 0 still had allocated for itself. > > In order to avoid this, emit the "free xxxxxx" tracing report just > before the actual call to free the memory, instead of just after it. > > Signed-off-by: Yunfeng Ye > Reviewed-by: Vlastimil Babka > --- > v1 -> v2: > - Modify the description > - Add "Reviewed-by" > > mm/slub.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 432145d7b4ec..427e62034c3f 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -3526,8 +3526,8 @@ void kmem_cache_free(struct kmem_cache *s, void *x) > s = cache_from_obj(s, x); > if (!s) > return; > - slab_free(s, virt_to_head_page(x), x, NULL, 1, _RET_IP_); > trace_kmem_cache_free(_RET_IP_, x, s->name); > + slab_free(s, virt_to_head_page(x), x, NULL, 1, _RET_IP_); > } It seems that kmem_cache_free() in mm/slab.c has the same problem. We can fix it. Thanks. > EXPORT_SYMBOL(kmem_cache_free); >