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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=MNFv1+fc; 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 45AD5606A31D for ; Fri, 30 Oct 2026 13:42:54 +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=MNFv1+fc Received: by smtp.kernel.org (Postfix) with ESMTPSA id 32C421F000C1; Fri, 30 Oct 2026 13:42:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793367774; bh=69PaK2GDhFAEWGlSb6meYzT+lKafyCgwdL+hSzCGmnA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=MNFv1+fctK3t4SBo6+onmKHPTHA/OyS8sVWH3lCZr6+1qxzBi5FkMQOa8Lt8QfQEo cJgW2vzLkLZNWONBtv5p2AjwIacI0jOG/itLfS4/1YzBSBEagEy9kSanhoKw5sR+Xr w2f+tKfE57CA2RqmPlupaQSO1mUUwharocqrrN2J0/hIAmWRh5QefEmrBLN5x+CspA ZMhMfoFNA+CHrWduFEjLRXe3Iuy15Fs/q5jXwsdpEmqzQOrp+4/eyKWH2Ijt6kXkh9 Ay/+RTar/1xcXNCnsqwSTbBnAiDAu51jakK+FRoQvb9ahbxGkbWzPEonxaUyakaYQg UvteOnqDNRh+A== Message-ID: <172b2180-a15e-4b7c-98a2-ee62090057d3@kernel.org> Date: Fri, 30 Oct 2026 14:42:50 +0100 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 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 7/9] w1: don't hold list_mutex while a slave is torn down To: Greg Kroah-Hartman Cc: Josef Bacik , linux-kernel@vger.kernel.org, stable References: <20261027-llm-char-misc-w1-v1-0-d2e6bfafb6a4@linuxfoundation.org> <20261027-llm-char-misc-w1-v1-7-d2e6bfafb6a4@linuxfoundation.org> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 27/10/2026 17:04, Greg Kroah-Hartman wrote: > From: Josef Bacik > > When the last reference to a slave is dropped, w1_unref_slave() holds > list_mutex of the master until the slave has been freed. In between it > calls the ->remove_slave() callback of the family driver and > device_unregister(). Both wait for others: for the sysfs callbacks > which are running, and in the case of w1_therm also for the file > therm_bulk_read of the master and for everybody who is talking to the > sensor. None of those can therefore take list_mutex, although the > callbacks of therm_bulk_read walk the list which it protects. > > The mutex is only needed to make the decrement of the reference count and > the removal from the list one step for w1_search_slave() and > w1_slave_search_device(), which look the slave up in the list and, in the > first case, take a reference. Once the slave is off the list, nobody can > find it any more. Drop the mutex at that point. > > The callers which hold the mutex of the master, which serialises > attaching and detaching, are not affected. The one which does not is > w1_process_cb(), when it drops the last reference to a slave which has > been detached while a netlink command for it was queued. Somebody who > attaches a slave with the same ID through sysfs or netlink at that very > moment used to wait until the old device was gone. Now the registration > of the new device may fail because the name is still in use. > > This is a preparation for "w1: w1_therm: lock the list of slaves for the > bulk read". > > Cc: stable > Signed-off-by: Josef Bacik > Signed-off-by: Greg Kroah-Hartman Reviewed-by: Krzysztof Kozlowski Best regards, Krzysztof