From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C277A3988FE; Wed, 4 Mar 2026 09:52:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772617939; cv=none; b=UNTtQYjQ+jQc0bahhY6uGsMS2+Ckd9WazCXrUL4OjSmUVi3SBUm2U/Jx+nb+SjRv5EpaiqA90MjKhVqZIUnMd9QFbtM74xjEsCONk+FaRvdsUmQm+khRvV8zVQ69ul1A8/WKF3yDvJxF+c/f9MLShzRA7e6o2vgfCRPvYidm8mw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772617939; c=relaxed/simple; bh=3uY/ZReqQuF/VaLAKNwfGyuwdnkEsCVU52pytEoQ8CY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=N0EL23KN2oP499qsE5IhTIp5ngfBQ42BNTXNpq825vAc8qZKRyalz3w0AmXbkki36h0nXeh0Fvb/f5IwPMFUpkUsyPv2+eG4xqAjNV58arOT7IWFkHQkmRa+ODRW127i2t4GOq6q4xxXrP8pfmStY4utZ77NoWHcgXo9gNf1VaA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=aviDvS8+; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="aviDvS8+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3803FC19423; Wed, 4 Mar 2026 09:52:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772617939; bh=3uY/ZReqQuF/VaLAKNwfGyuwdnkEsCVU52pytEoQ8CY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=aviDvS8+cAwFW35VY4fUmcMNDkisZaDchfVzfAwWW/UcC7NRJ1GRP8PGeJn4Cnem8 SelB+ms63SLP9JrQNhe7zOltYCtDk7qsdycfPCQsoSvzMwqHRAMbSrktk0DEql4o83 CEx426o0bPhq1ayjaoazqcz6polxkg4DTdLLYvhs7KJK4WjaEGRVm42sr0zG1V58/G i53KVeGa5NZW6VI1lTIZ/uPdJicpZNingWDIKx8ng8pq+p+z/Sg6iZAyGmXA6vocUR EVFpEaNp8eBdIImKXx2lZHqTnqPuHPMUk2Ni+YkrFWtWNGPaQFZfHhBn5yO6IjA5Z6 7goQ4ZCVUpDUw== Message-ID: <391b74b8-eb4b-4510-9cc8-3483f6605748@kernel.org> Date: Wed, 4 Mar 2026 18:52:16 +0900 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] scsi: core: Fix async_scan race condition with READ_ONCE/WRITE_ONCE To: Chaohai Chen , John Garry Cc: James.Bottomley@hansenpartnership.com, martin.petersen@oracle.com, bvanassche@acm.org, hch@infradead.org, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260304075712.3039960-1-wdhh6@aliyun.com> <2885ac50-2326-4548-b92c-c5ae566a8013@oracle.com> Content-Language: en-US From: Damien Le Moal Organization: Western Digital Research In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/4/26 18:43, Chaohai Chen wrote: > On Wed, Mar 04, 2026 at 09:20:25AM +0000, John Garry wrote: >> On 04/03/2026 07:57, Chaohai Chen wrote: >>> Previously, host_lock was used to prevent bit-set conflicts in async_scan, >>> but this approach introduced naked reads in some code paths. >>> >>> Convert async_scan from a bitfield to a bool type to eliminate bit-level >>> conflicts entirely. Use READ_ONCE() and WRITE_ONCE() to ensure proper >>> memory ordering on Alpha and satisfy KCSAN requirements. >> >> Is the shost->scan_mutex always held when shost->async_scan is read/written? >> > Yes. In theory, there is no need for READ-ONCE/WRITE-ONCE. Plus, this belongs > to defensive programming. And it indicates that this is a shared variable, > which means that this variable will be accessed by multiple threads and > concurrency issues need to be handled carefully. If the scan_mutex is always held when scan_mutex is used, there will not be multiple threads, unless there are accessed also from IRQ context, which would be odd. So I am not sure what concurrency issue you are referring to here. -- Damien Le Moal Western Digital Research