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([2001:a61:1363:9e01:43f1:e533:276c:e9a1]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4851ad2b26dsm41681205e9.31.2026.03.05.04.44.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Mar 2026 04:44:32 -0800 (PST) Message-ID: <678e1fc6-356d-426a-aec0-f0bf46c7d3af@suse.com> Date: Thu, 5 Mar 2026 13:44:31 +0100 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [BUG] usb: cdc-wdm: Missing barriers in ad-hoc lockless buffer To: Gui-Dong Han , Oliver Neukum Cc: Greg KH , robert.hodaszi@digi.com, kees@kernel.org, linux-usb@vger.kernel.org, LKML , Jia-Ju Bai References: Content-Language: en-US From: Oliver Neukum In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 05.03.26 13:28, Gui-Dong Han wrote: > Specifically, wdm_read() accesses ->length and then ->flags, often > without holding ->iuspin. Similarly, wdm_in_callback() involves > multiple accesses to both. > > I am indeed nervous about this pattern. Without barriers, changes to > these associated fields made on one CPU might be observed in a > completely different order on another CPU. OK, I rechecked. And indeed it seems to me like setting WDM_OVERFLOW and WDM_READ could be reordered with respect to each other in wdm_in_callback() and that must not happen. What do you think? Regards Oliver