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([2001:a61:1340:dc01:654b:3cf0:59cd:498]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49ce554d52esm282573745e9.3.2026.09.07.05.46.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Sep 2026 05:46:18 -0700 (PDT) Message-ID: Date: Mon, 7 Sep 2026 14:46:16 +0200 Precedence: bulk X-Mailing-List: stable@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 13:38, Johan Hovold wrote: > On Mon, Sep 07, 2026 at 12:28:46PM +0200, Oliver Neukum wrote: >> >> >> On 07.09.26 12:01, Johan Hovold wrote: >>> On Mon, Sep 07, 2026 at 11:50:41AM +0200, Oliver Neukum wrote: >> 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. > > Yes, the completion handler needs to handle the status change (i.e. > compare new and previous status and increment the counters), but it > shouldn't update any old *icount* structure. We could do that and it would indeed be simpler. But it would change the semantics so that past status changes no longer show up in TIOCMIWAIT. Is that really a good idea? Regards Oliver