From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793810114; b=NDvbFUaRFLs8nNyNUBmlyAsM6DX+w0bWkSZQtc326b58er2yCudBQtFbLkHkv7bxlELt 6HZKzp7TgglkABOty9WYpZDvKINmd7/Z65ayhjqUu0+T3+ttwuHV/epXvpX093pHIJd3W USOWXXeIx8A7wKPJ9vAEybcqaZVRmc1W7jiHrAwsWoznol0TTUWLaWkIYaoGcIqEzllgz SzTqv5imLRy7ujueizk4nXTh8kBEk3qmzv73/IDOfikwN58I7umLpq6xa8OrxqpaRPiRC 8RRAGooQm+xNJVqKa9GsnxY61ws5efDn8Y0dvImqWQi1QEwgWr4Nqzx+9MJYGzIRMYQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793810114; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=8bvMUN4Wk0BgGgF1RgcQrwazIY2aEPvQvSEkNPHOui0=; b=1w7xhQPbEIshvjd/IOzC93cvgZVXexBGBKsP3pu9qVhJLeptphFb84lt/FmYtvPuQeU9 hf7tvemNBPZN0qa/EQLKSb5uBjic8w5Z2ZicrohVFoJZGaI3qYoUCJAiXczBjh+NJ/9fF buTmiJwZA/L3V/Z7Cm9RcvGFfvm9Oyaoj4pI7thlsdHns5VcFZdj1Cx0c4sXx8m+bv2cK XAWjj7EDXnAv96nUvjLbVKpvB62qRHfO6u7V/h8vlwsS/l9T3CNYhXcjnMOT/9nseA2Q1 PpS3UEBh6Rb1SBvyduf2ltU9YKwPPIvTDFR8BWSAgxvbw1BSBY3+rdW7h4dWmvNLrCw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=H3upLpGT; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CB92C606A32C for ; Wed, 4 Nov 2026 16:35:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=H3upLpGT Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3BD641F00919; Wed, 4 Nov 2026 16:35:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793810113; bh=8bvMUN4Wk0BgGgF1RgcQrwazIY2aEPvQvSEkNPHOui0=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=H3upLpGTA18T3EdPjgIqGURFX6ukYjVdk4P/01EFshF+ivtLq6qY+nk8M3sk4aLzX RwE0YkeINt8rYueavFNh4X2mLUVn8+ivmbEw/uJO9w/YzViENqud/DUFDZeR+K7R1P wkpSKRc2AkIPhOMpRoRXp52AtCwpEAh84KRCtdtv57fqIdLVNVX5M9H8Nu0oc48qFs 3ausvv+JRE2zdKjXBOzLhOoTiZLf8xFgz7PII8xS4EztgpfilaJPScx7V7z+Sd3wC4 23/b4UnjLbBkyZ0bDViGXjRdJMy6NPkJZcxKu7rp4pP9NhfSsN2XEDUwwOCPvNlND7 2QVWrBW8ijxbQ== Date: Wed, 4 Nov 2026 09:35:11 -0700 From: Keith Busch To: Qiliang Yuan Cc: Christoph Hellwig , Sagi Grimberg , Chaitanya Kulkarni , linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] nvmet: drop the extra RCU grace period in nvmet_ns_disable() Message-ID: References: <20261104-bug-nvmet-ns-disable-rcu-v2-1-b158a59318ad@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261104-bug-nvmet-ns-disable-rcu-v2-1-b158a59318ad@gmail.com> On Wed, Nov 04, 2026 at 01:31:28AM -0500, Qiliang Yuan wrote: > nvmet_ns_disable() kills the namespace's percpu ref, waits in > synchronize_rcu() for anyone looking the namespace up under > rcu_read_lock(), and then waits for the ref to drop to zero. > > Killing a percpu ref that is still in percpu mode, as the namespace > ref always is until then, switches it to atomic mode from an RCU > callback, so the ref can't drop to zero before a grace period has > passed since the kill. synchronize_rcu() thus adds a second grace > period in a row, about 4 ms here, and disabling the namespaces of a > subsystem one by one takes about 9 ms each. > > Drop synchronize_rcu() and rely on the wait for the ref to cover the > RCU readers as well. Thanks, applied to nvme-7.4.