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([2001:a61:1366:6801:d8:8490:cf1a:3274]) by smtp.gmail.com with ESMTPSA id h15-20020a05600c314f00b00417ee886977sm13425859wmo.4.2024.04.15.03.14.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Apr 2024 03:14:49 -0700 (PDT) Message-ID: Date: Mon, 15 Apr 2024 12:14:48 +0200 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] usb: cdc-wdm: close race between read and workqueue To: =?UTF-8?Q?Bj=C3=B8rn_Mork?= , Oliver Neukum Cc: Aleksander Morgado , linux-usb@vger.kernel.org, gregkh@linuxfoundation.org, linux@roeck-us.net, linux-kernel@vger.kernel.org, ejcaruso@chromium.org References: <385a3519-b45d-48c5-a6fd-a3fdb6bec92f@chromium.org> <87mspvi0lk.fsf@miraculix.mork.no> <878r1fht93.fsf@miraculix.mork.no> Content-Language: en-US From: Oliver Neukum In-Reply-To: <878r1fht93.fsf@miraculix.mork.no> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 15.04.24 11:26, Bjørn Mork wrote: > Oliver Neukum writes: >> On 15.04.24 08:47, Bjørn Mork wrote: >> >>> urb from service_outstanding_interrupt(). That's why it was added. See >>> the explanation Robert wrote when introducing it: >>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/usb/class/cdc-wdm.c?id=c1da59dad0ebd3f9bd238f3fff82b1f7ffda7829 >> >> Well, the explanation is correct in that we must read >> data available. However, if the RESPONDING flag is set >> and the URB submitted, we are already doing so. > > Sounds reasonable. Except that the bug proves we didn't. Why? I am afraid I do not get that part. > If you are right that service_outstanding_interrupt can race againts > itself (and I don't doubt that), then I guess this could also happen > between failure to submit the URB and clearing the flag? Yes, it can. In fact in this case the behavior should not change. I am afraid we have a misunderstanding. It seems to me that in the unchanged driver the result of service_outstanding_interrupt() is undefined. Please explain. Regards Oliver