From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 84F3C606A32C for ; Tue, 3 Nov 2026 08:15:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=3TgxjSwS DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Unsubscribe-Post:List-Owner; bh=VVI2BEPcphI98oQDYKHMPWx770bBBVfS5vHEb2ZMpdw=; b=3TgxjSwSdoITBwUnzP3kwoHflH IvLWVm3Esw98dhHZZKd2EW9pIO9OeUbdyhqFqEFdfc3DsfC0LbzJ6kVHdm5RJvS1PkwNKNQ8YTF72 dKRpme2tjQZz0jAvysN7lQQim2Gu4kR5mF/6b2jpC7EuoHhWEVvr9xtfofuae8uSreIRbD+xqlck8 VfiJ9GInWcTyoEKElWxo4iAm9g3nN0wTs5kntcg6z+hjKRZvaSoN1Feta0wqljuLagpLY9EOjD4NZ F9Ch26dQXIhrY2l1cUQBsRRq5CcH76bA+otMX58fEzeaCHegtSeDexnO89bsLXQmFNh6p0p24MPzi DfzBXtwQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xO9gQ-00000001W5Z-2gOL; Tue, 03 Nov 2026 08:15:54 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xO9gM-00000001W4L-3UmX for linux-nvme@lists.infradead.org; Tue, 03 Nov 2026 08:15:52 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 8055868CFE; Tue, 3 Nov 2026 09:15:47 +0100 (CET) Date: Tue, 3 Nov 2026 09:15:46 +0100 From: Christoph Hellwig To: Qiliang Yuan Cc: Christoph Hellwig , Sagi Grimberg , Chaitanya Kulkarni , linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] nvmet: drop the extra RCU grace period in nvmet_ns_disable() Message-ID: <20261103081546.GC4301@lst.de> References: <20261103-bug-nvmet-ns-disable-rcu-v1-1-ff7ac5623923@gmail.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261103-bug-nvmet-ns-disable-rcu-v1-1-ff7ac5623923@gmail.com> User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261103_001551_019005_DC65FF75 X-CRM114-Status: GOOD ( 17.00 ) X-Spam-Score: -1.9 (-) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" X-Spam-Status: No, score=-5.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_EF,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Tue, Nov 03, 2026 at 01:31:25AM -0500, Qiliang Yuan wrote: > * Now that we removed the namespaces from the lookup list, we > * can kill the per_cpu ref and wait for any remaining references > - * to be dropped, as well as a RCU grace period for anyone only > - * using the namespace under rcu_read_lock(). Note that we can't > - * use call_rcu here as we need to ensure the namespaces have > - * been fully destroyed before unloading the module. > + * to be dropped. Rely on that wait for anyone only using the > + * namespace under rcu_read_lock() too: the ref can't drop to zero > + * before an RCU grace period has passed since the kill. Note that > + * we can't use call_rcu here as we need to ensure the namespaces > + * have been fully destroyed before unloading the module. > */ > percpu_ref_kill(&ns->ref); > - synchronize_rcu(); This assumes the percpu_ref is never moved to atomic mode otherwise. Which we don't do in nvmet, but maybe leaving a reminder of that here would be useful.