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[2620:137:e000::1:20]) by mx.google.com with ESMTP id om8-20020a17090b3a8800b002448c09e0f0si86046pjb.168.2023.04.05.19.09.55; Wed, 05 Apr 2023 19:10:08 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234651AbjDFB5M (ORCPT + 99 others); Wed, 5 Apr 2023 21:57:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58144 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234539AbjDFB5F (ORCPT ); Wed, 5 Apr 2023 21:57:05 -0400 Received: from dggsgout11.his.huawei.com (dggsgout11.his.huawei.com [45.249.212.51]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0A46283CE for ; Wed, 5 Apr 2023 18:57:02 -0700 (PDT) Received: from mail02.huawei.com (unknown [172.30.67.169]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4PsPkf381dz4f3v5b for ; Thu, 6 Apr 2023 09:56:58 +0800 (CST) Received: from huaweicloud.com (unknown [10.175.127.227]) by APP3 (Coremail) with SMTP id _Ch0CgCnUyHoJi5kX936GA--.31319S6; Thu, 06 Apr 2023 09:56:59 +0800 (CST) From: Ye Bin To: dennis@kernel.org, tj@kernel.org, cl@linux.com, linux-mm@kvack.org, yury.norov@gmail.com, andriy.shevchenko@linux.intel.com, linux@rasmusvillemoes.dk Cc: linux-kernel@vger.kernel.org, dchinner@redhat.com, yebin10@huawei.com, yebin@huaweicloud.com Subject: [PATCH v2 2/2] lib/percpu_counter: fix dying cpu compare race Date: Thu, 6 Apr 2023 09:56:29 +0800 Message-Id: <20230406015629.1804722-3-yebin@huaweicloud.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20230406015629.1804722-1-yebin@huaweicloud.com> References: <20230406015629.1804722-1-yebin@huaweicloud.com> MIME-Version: 1.0 X-CM-TRANSID: _Ch0CgCnUyHoJi5kX936GA--.31319S6 X-Coremail-Antispam: 1UD129KBjvJXoW7ZFW7ArWDXw1ktFy7KFyfZwb_yoW8WFy5pr 4UKry5Jr18AF92k343Kw1vqF9I9r1kAF4rKwnrGF1fAFnxZa45urW0yrs8JF109rn7Wrya qryjgF4xCa4Yv3JanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUBE14x267AKxVWrJVCq3wAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2048vs2IY020E87I2jVAFwI0_Jryl82xGYIkIc2 x26xkF7I0E14v26ryj6s0DM28lY4IEw2IIxxk0rwA2F7IY1VAKz4vEj48ve4kI8wA2z4x0 Y4vE2Ix0cI8IcVAFwI0_tr0E3s1l84ACjcxK6xIIjxv20xvEc7CjxVAFwI0_Gr1j6F4UJw A2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x0267AKxVW0oVCq3wAS 0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0I7IYx2 IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFVCjc4AY6r1j6r4UM4x0 Y48IcxkI7VAKI48JM4x0x7Aq67IIx4CEVc8vx2IErcIFxwACI402YVCY1x02628vn2kIc2 xKxwCF04k20xvY0x0EwIxGrwCFx2IqxVCFs4IE7xkEbVWUJVW8JwC20s026c02F40E14v2 6r1j6r18MI8I3I0E7480Y4vE14v26r106r1rMI8E67AF67kF1VAFwI0_Jw0_GFylIxkGc2 Ij64vIr41lIxAIcVC0I7IYx2IY67AKxVWUJVWUCwCI42IY6xIIjxv20xvEc7CjxVAFwI0_ Gr0_Cr1lIxAIcVCF04k26cxKx2IYs7xG6r1j6r1xMIIF0xvEx4A2jsIE14v26r1j6r4UMI IF0xvEx4A2jsIEc7CjxVAFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf9x0JUHbyAUUUUU = X-CM-SenderInfo: p1hex046kxt4xhlfz01xgou0bp/ X-CFilter-Loop: Reflected X-Spam-Status: No, score=0.0 required=5.0 tests=SPF_HELO_NONE,SPF_NONE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1762390975563691343?= X-GMAIL-MSGID: =?utf-8?q?1762390975563691343?= From: Ye Bin In commit 8b57b11cca88 ("pcpcntrs: fix dying cpu summation race") a race condition between a cpu dying and percpu_counter_sum() iterating online CPUs was identified. Acctually, there's the same race condition between a cpu dying and __percpu_counter_compare(). Here, use 'num_online_cpus()' for quick judgment. But 'num_online_cpus()' will be decreased before call 'percpu_counter_cpu_dead()', then maybe return incorrect result. To solve above issue, also need to add dying CPUs count when do quick judgment in __percpu_counter_compare(). Signed-off-by: Ye Bin --- lib/percpu_counter.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c index 5004463c4f9f..399840cb0012 100644 --- a/lib/percpu_counter.c +++ b/lib/percpu_counter.c @@ -227,6 +227,15 @@ static int percpu_counter_cpu_dead(unsigned int cpu) return 0; } +static __always_inline unsigned int num_count_cpus(void) +{ +#ifdef CONFIG_HOTPLUG_CPU + return (num_online_cpus() + num_dying_cpus()); +#else + return num_online_cpus(); +#endif +} + /* * Compare counter against given value. * Return 1 if greater, 0 if equal and -1 if less @@ -237,7 +246,7 @@ int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch) count = percpu_counter_read(fbc); /* Check to see if rough count will be sufficient for comparison */ - if (abs(count - rhs) > (batch * num_online_cpus())) { + if (abs(count - rhs) > (batch * num_count_cpus())) { if (count > rhs) return 1; else