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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 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 X-BeenThere: linux-erofs@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Development of Linux EROFS file system List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jeff Layton , linux-kernel@vger.kernel.org, dhowells@redhat.com, linux-cachefs@redhat.com, houtao1@huawei.com, linux-erofs@lists.ozlabs.org Errors-To: linux-erofs-bounces+linux-erofs=archiver.kernel.org@lists.ozlabs.org Sender: "Linux-erofs" 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