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 66D3DC5479D for ; Wed, 11 Jan 2023 16:10:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232621AbjAKQKm (ORCPT ); Wed, 11 Jan 2023 11:10:42 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53448 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231747AbjAKQKj (ORCPT ); Wed, 11 Jan 2023 11:10:39 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D816B109D for ; Wed, 11 Jan 2023 08:09:52 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1673453392; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ED6zPjm7mtrHMK8B7KMZYr4k0FzaJh6lrc0c3Lwxsxo=; b=Wn/UbK8giO1JbFdUJ+QRT/74+2tRnT4bldh+ouwcyADwouX9wR69N36bQOPtMqBpLeyPpA WI/e/qoPLE1GCGPSyhSieGGJZR+r+RRmD4o5BlNIZtEr3Dgi7zWye5Heyq9p/+LETmAJVA J5Q5+04byDOfUAeWa763V4sFPDwVbR4= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-380-5CDp3c7XNkOWDTcWvnPtIg-1; Wed, 11 Jan 2023 11:09:48 -0500 X-MC-Unique: 5CDp3c7XNkOWDTcWvnPtIg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 7332C381494F; Wed, 11 Jan 2023 16:09:48 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.87]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7E2F040C115E; Wed, 11 Jan 2023 16:09:47 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20221226103309.953112-3-houtao@huaweicloud.com> References: <20221226103309.953112-3-houtao@huaweicloud.com> <20221226103309.953112-1-houtao@huaweicloud.com> To: Hou Tao Cc: dhowells@redhat.com, linux-cachefs@redhat.com, Jeff Layton , linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org, Jingbo Xu , houtao1@huawei.com Subject: Re: [PATCH v2 2/2] fscache: Add the missing smp_mb__after_atomic() before wake_up_bit() MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <2431993.1673453386.1@warthog.procyon.org.uk> Date: Wed, 11 Jan 2023 16:09:46 +0000 Message-ID: <2431994.1673453386@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. David