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([2001:a61:137b:5001:be5a:c750:b487:ff1b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3680db04841sm8924139f8f.101.2024.07.16.05.44.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 16 Jul 2024 05:44:51 -0700 (PDT) Message-ID: <3073c8ce-1923-4816-a442-41b4cc333af9@suse.com> Date: Tue, 16 Jul 2024 14:44:50 +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 next] usb: usbfs: Add reset_resume for usbfs To: Alan Stern , Oliver Neukum Cc: Hongyu Xie , gregkh@linuxfoundation.org, brauner@kernel.org, jlayton@kernel.org, jack@suse.cz, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org References: <20240711084321.44916-1-xiehongyu1@kylinos.cn> <527927b8-9475-47da-bf2b-7a5d9e81e470@suse.com> <9ef72886-13b8-46cf-a0aa-54dad36102e9@rowland.harvard.edu> <2a80d11d-029f-4e7e-9a8e-3abae1034add@suse.com> <429eb27a-578a-4208-8ce1-89434b8d739f@rowland.harvard.edu> Content-Language: en-US From: Oliver Neukum In-Reply-To: <429eb27a-578a-4208-8ce1-89434b8d739f@rowland.harvard.edu> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 15.07.24 16:22, Alan Stern wrote: > On Mon, Jul 15, 2024 at 10:53:14AM +0200, Oliver Neukum wrote: >> >> >> On 11.07.24 16:41, Alan Stern wrote: >>> Agreed, but the solution is pretty simple. Because the device was >>> suspended, the userspace driver must have enabled suspend via the >>> USBDEVFS_ALLOW_SUSPEND ioctl. >> >> The whole system could have been suspended, in particularly to S4. > > You are right. I was thinking of runtime suspend, not system suspend. > My mistake. This is at the intersection of several scenarios. That is a good part of what makes this difficult. In principal I think we could get away with checking for a flag to be set at reset_resume() before each operation. Elegant this is not. Yet, it seems to me like the race necessarily exists and is unsolvable in user space. Furthermore in the long run, if we want to use D3cold in runtime power management, it looks to me like we would want a second permission ioctl for that. Regards Oliver