From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 66A063AA1A7; Mon, 7 Sep 2026 08:47:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788770873; cv=none; b=K4chEHHPCf/whVUFTIji41PBHOZDcBL8yQ++FEDxVaLEpmKe1Vbgfu0hH3IoXPHpu2gEzWzs7UXHTEVfN9LFYbkGwmb2H4IRKkT27w9NtHwOtf6WZvctNvG6QGQn/lOrnPLp5Za8TNRY7QaHtvkGDuGFdnZXfkzR9YIf9zsa+r4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788770873; c=relaxed/simple; bh=Gb9Auh5ZNXWHXHOOwQE32rxToV+hQ0pGd9M/BCS1nJw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=cgXOv/mPXWs1FvY98inVbGwC7kVq23/C7ABsdiX14gEmESOSogJyk5SNHVbrVfoV30iIo+f7ZU6IgPrCrxD8VXsQBDluqKvAQIY4M/m2wnc1uBNB/+MPtXzLaPcptlB0BrDlae/4nBfIpGW/LM+fya/8QIZA44dqeZJLwNjiwFE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GXZfYcPG; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GXZfYcPG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 173D31F00A3A; Mon, 7 Sep 2026 08:47:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788770872; bh=Bf6fIph90GFv45/3lNjQ8b5NbyisSGZ3v2BSDp0jkbA=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=GXZfYcPGffP3RD77IEVgWgvCRjTgLEnnaiZhU1EyJMr/jqZY43VjtzYh05kwvRKzm JTERkAApMJ3DpIFZlUEYhClts9WLzFZxVM5nJ+rQSa7Rj89WAv0WLW25Rh89NCmFb8 IQ4gJA/KO/jPqlhoXBe1+COex29Nc+Y7Tut60P6dwZneyNwOCXj8pG5kFztfUAxuQH lci+xAiNwvDJa34AI5vwuRZ745bYHxetI34isufCRjpCN+HsDUyn/AaH3hnZbr3Der av45lPbsG/Cwn0h5E2aKFeCe8MtMyOZNdlV8sK5kF6OAS/NRnUD8rtPVSdzLwXKOW0 OQ6p/WnL3piew== Received: from johan by xi.lan with local (Exim 4.99.4) (envelope-from ) id 1x3V13-00000000UOX-36CK; Mon, 07 Sep 2026 10:47:49 +0200 Date: Mon, 7 Sep 2026 10:47:49 +0200 From: Johan Hovold To: Oliver Neukum Cc: Greg Kroah-Hartman , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] USB: cdc-acm: fix racy TIOCMIWAIT implementation Message-ID: References: <20260907065501.101013-1-johan@kernel.org> Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Sep 07, 2026 at 10:17:38AM +0200, Oliver Neukum wrote: > On 07.09.26 08:55, Johan Hovold wrote: > > The wakeup condition needs to be checked after adding the task to the > > waitqueue and updating the task state to avoid missing a racing modem > > status update or disconnect. > > I am sorry, but in this case I have to ask: > Isn't TIOCMIWAIT inherently racy against the hardware? What do you mean? 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. Johan