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([2001:a61:1340:dc01:654b:3cf0:59cd:498]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4858d312ca0sm27384160f8f.4.2026.09.07.03.28.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Sep 2026 03:28:47 -0700 (PDT) Message-ID: Date: Mon, 7 Sep 2026 12:28:46 +0200 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: [PATCH] USB: cdc-acm: fix racy TIOCMIWAIT implementation To: Johan Hovold , Oliver Neukum Cc: Greg Kroah-Hartman , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260907065501.101013-1-johan@kernel.org> <72615ee3-46eb-4639-a408-ba29c1235d08@suse.com> Content-Language: en-US From: Oliver Neukum In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 07.09.26 12:01, Johan Hovold wrote: > On Mon, Sep 07, 2026 at 11:50:41AM +0200, Oliver Neukum wrote: >> On 07.09.26 10:47, Johan Hovold wrote: >>> On Mon, Sep 07, 2026 at 10:17:38AM +0200, Oliver Neukum wrote: >>>> On 07.09.26 08:55, Johan Hovold wrote: [..] >>> Looking at the implementation again now, it seems further changes are >>> needed to fix the implementation, though. The completion handler should >>> not be updating old_count. That's for each TIOCMIWAIT to do. >> >> I am sorry to be obnoxious about that, but I am afraid that would >> break TIOCGICOUNT > > Why do you think so? TIOCGICOUNT just returns the current counters. Yes, but user space can call TIOCGICOUNT multiple times in sequence _without_ calling TIOCMIWAIT in between. In that case the counters have to increase if a line changes, don't they? For that to happen you need to handle a status change in the completion handler. Regards Oliver