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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DEAFDC5479D for ; Thu, 12 Jan 2023 01:07:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236094AbjALBHm (ORCPT ); Wed, 11 Jan 2023 20:07:42 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44224 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234975AbjALBHj (ORCPT ); Wed, 11 Jan 2023 20:07:39 -0500 Received: from dggsgout11.his.huawei.com (dggsgout11.his.huawei.com [45.249.212.51]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9CE5C11C2C for ; Wed, 11 Jan 2023 17:07:38 -0800 (PST) Received: from mail02.huawei.com (unknown [172.30.67.153]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4NsmcN64PTz4f3k6B for ; Thu, 12 Jan 2023 09:07:32 +0800 (CST) Received: from [10.174.176.117] (unknown [10.174.176.117]) by APP4 (Coremail) with SMTP id gCh0CgDXP7NUXb9j77E5Bg--.63722S2; Thu, 12 Jan 2023 09:07:35 +0800 (CST) Subject: Re: [PATCH v2 2/2] fscache: Add the missing smp_mb__after_atomic() before wake_up_bit() To: David Howells Cc: linux-cachefs@redhat.com, Jeff Layton , linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org, Jingbo Xu , houtao1@huawei.com References: <20221226103309.953112-3-houtao@huaweicloud.com> <20221226103309.953112-1-houtao@huaweicloud.com> <2431994.1673453386@warthog.procyon.org.uk> From: Hou Tao Message-ID: Date: Thu, 12 Jan 2023 09:07:32 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <2431994.1673453386@warthog.procyon.org.uk> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-CM-TRANSID: gCh0CgDXP7NUXb9j77E5Bg--.63722S2 X-Coremail-Antispam: 1UD129KBjvdXoWrZF4rAF15Zr1ftr1rCr1kuFg_yoW3KFb_CF ZYvFZYkw47W3WDK3WUtr1Sqa1xKr18C3Z3trZrJrZ7tr4xZ39IkFn7WryI9F1xG3s7KF43 A34UWF4vyw13CjkaLaAFLSUrUUUUUb8apTn2vfkv8UJUUUU8Yxn0WfASr-VFAUDa7-sFnT 9fnUUIcSsGvfJTRUUUbzAYFVCjjxCrM7AC8VAFwI0_Gr0_Xr1l1xkIjI8I6I8E6xAIw20E Y4v20xvaj40_Wr0E3s1l1IIY67AEw4v_Jr0_Jr4l8cAvFVAK0II2c7xJM28CjxkF64kEwV A0rcxSw2x7M28EF7xvwVC0I7IYx2IY67AKxVWDJVCq3wA2z4x0Y4vE2Ix0cI8IcVCY1x02 67AKxVW8Jr0_Cr1UM28EF7xvwVC2z280aVAFwI0_GcCE3s1l84ACjcxK6I8E87Iv6xkF7I 0E14v26rxl6s0DM2AIxVAIcxkEcVAq07x20xvEncxIr21l5I8CrVACY4xI64kE6c02F40E x7xfMcIj6xIIjxv20xvE14v26r106r15McIj6I8E87Iv67AKxVWUJVW8JwAm72CE4IkC6x 0Yz7v_Jr0_Gr1lF7xvr2IY64vIr41lc7I2V7IY0VAS07AlzVAYIcxG8wCF04k20xvY0x0E wIxGrwCFx2IqxVCFs4IE7xkEbVWUJVW8JwC20s026c02F40E14v26r1j6r18MI8I3I0E74 80Y4vE14v26r106r1rMI8E67AF67kF1VAFwI0_JF0_Jw1lIxkGc2Ij64vIr41lIxAIcVC0 I7IYx2IY67AKxVWUJVWUCwCI42IY6xIIjxv20xvEc7CjxVAFwI0_Gr0_Cr1lIxAIcVCF04 k26cxKx2IYs7xG6Fyj6rWUJwCI42IY6I8E87Iv67AKxVWUJVW8JwCI42IY6I8E87Iv6xkF 7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjxUOyCJDUUUU X-CM-SenderInfo: xkrx3t3r6k3tpzhluzxrxghudrp/ X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 1/12/2023 12:09 AM, David Howells wrote: > Hou Tao wrote: > >> fscache_create_volume_work() uses wake_up_bit() to wake up the processes >> which are waiting for the completion of volume creation. According to >> comments in wake_up_bit() and waitqueue_active(), an extra smp_mb() is >> needed to guarantee the memory order between FSCACHE_VOLUME_CREATING >> flag and waitqueue_active() before invoking wake_up_bit(). > What two values are you ordering? > > If we're using this to create a critical section, then yes, we would need a > barrier to order the changes inside the critical section before changing the > memory location that forms the lock - but this is not a critical section. It is similar with patch #1. The smp_mb() is used for order between volume->flags and wq->head. > David >