From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qt1-f179.google.com (mail-qt1-f179.google.com [209.85.160.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B04011624DF for ; Mon, 24 Aug 2026 00:29:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.160.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787531393; cv=none; b=nVG95VXGrF63q2T1K7/BOkVus4jmN6ELr5UcnfP/xqd6IJ22sKzczJPrhwjH+6hUO5DvUd7loAGhkcSerVge0WljJEMgU9tUPpqKPmefkpXpra4dMMtB3d6HIyVip0A+A6BbDFdUni7jjtZZqTVI/wVPgtoNFXIY+0P8HLn3SYg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787531393; c=relaxed/simple; bh=S2VVXIm9NXC1/7S/os++vXO4y8V6rLx/oQUPCR5sBQg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=m1ZaDBIPI36DXGLP472TtVa6Tu1ERD/nPVk2qKWgVHASwPm4yO6fGXzJZ02SNW1AStnXOlwyfpeHSr6eXU3EbeyFKdkSYFhWu/U77472aVYnmYinbSKdpEv+XGSmhXNkVRZ9ar7JHy1hPC7hyv5fd6wNJlVpyY1vE/pAdYmwZ5o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=rowland.harvard.edu; spf=fail smtp.mailfrom=g.harvard.edu; dkim=pass (2048-bit key) header.d=rowland.harvard.edu header.i=@rowland.harvard.edu header.b=tFfgQyKk; arc=none smtp.client-ip=209.85.160.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=rowland.harvard.edu Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=g.harvard.edu Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=rowland.harvard.edu header.i=@rowland.harvard.edu header.b="tFfgQyKk" Received: by mail-qt1-f179.google.com with SMTP id d75a77b69052e-5276d598b96so14111891cf.3 for ; Sun, 23 Aug 2026 17:29:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rowland.harvard.edu; s=google; t=1787531389; x=1788136189; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=u0oyaTfgHNj82lNrvA/IiuK50TaUKsX5aQhkbMM0CdQ=; b=tFfgQyKkG21HQZUundOLVyqOin2qKQ0MJFBydV2CDA5QHCmIlcsjIhV/BfJWaqQxHo c8CaVoSwIMkY7EElZQ4zoKc/jfPoG1EhUYofuBoJAS2p88D+mWVuBTc4NlB3WknYMQnG 6CVEYBIBs2UfV2ck/b46KWUOw0hYGaqcJkZFNLlDGKQszYWc9j7jNzTcAFDww538Ptx0 Perjv2XhvK1hAxxbwy+PYBpa+qAu8fayVv9ruZPYg8Rt/+yBmpm17opEXVyL/0nvyq5I hwx04qBMuiZAVeKC/8+uYHRvN5G7wgC5qEnKx8gALxBuByLdkwc+Rm3oFTsfHGdUBM12 VdRg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1787531389; x=1788136189; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=u0oyaTfgHNj82lNrvA/IiuK50TaUKsX5aQhkbMM0CdQ=; b=ZPRy5iMq1vVSOabkvZOAWzgm96jNC+9A/dWv+/b+Uhewp8FejGuYQBZK5oJm6g2l7P 7rLqk2yrYd4UIi0m1AfqZ3O00nFzkIrSKqrYC2d+5J9qpxpXHZcRKlv9os8S5blfux2f oRkJHtNjIvk4pYh6j9FmcdoaTwecSnYtWFmU3wJXDijSOZEImo+w5su2PeIJzZZYJOKU BT6unhaHTuK0O2qJp1Ie0oR2pNiPMoxy6ClHALVZ0eHLocEQxCrSJhx54armOwpLeMDW O8hm6wrUs74SZARpChabubfttyNo+hA3ny4ZaLuFlh5QfFh5h1Fy1L8LgJSVoc7oZ8uT dBbg== X-Forwarded-Encrypted: i=1; AHgh+RrsSgRp2g+J1eMWX7D8yyyAm2ZYL50Ue7jGeuQ2v1vTC3ugu/zwPg/RO0yOSYIfjKkL9WZAB1jQgoj9tqs=@vger.kernel.org X-Gm-Message-State: AFuF++m90NPItpYSBBtRI8EF844eMscbspfVDfXxOTB7rjPRovTyImFi bKmfFuV4GWblci1EX2Ru7tGZ52mOG9ut/Wsqs+Do1DczbCaHonT0JUOOnjRjX5RkYA== X-Gm-Gg: AR+sD133kaQAMUvsXYB3h+L1//QtjkmyYmOHa80xFTJ3hVCqhPt7zyUdLIAHQDTmW89 I+gVhlRmMi6YWNOW6lO7RnaJGqkUQ2Ds+mzQWXu/byZ6/I6/XWYtAEZnLOxBYJSC4EI+s0k5LTV BW8FFjbplG8zbLBkMw7LGXP8hpW93wjEAlIgGAD86K8BG4zZA7khdBWkEenq7H1v/uZs/nvu9x/ xZdYesIirNcEBWpDcLD2Gk3Epm7J2rOMczF6CPfSA9MU0TSMZhEaY5RntaW3ojF/DyVT/2/4KWR BxpiubE6mhjXPdphafOo9zemxqCACyhbeKqC64bbaK1ETv//tYr0wPAJpLteV6ae0lX9ErrnQtX fNanWqYhyNNwUqjDLJkksH+onRk6GqBv79igrjLETXw3Q9aSCRIlWd1ck1kZjunmuQqrFCnnA99 f+0bHPViZniR9xRPZN9yjnG45g5pj0ilXuvU89k3nVvWv+Pl0TOnCUTvpVoAd8W9fHAkyaMMQa X-Received: by 2002:a05:622a:4083:b0:52b:6543:d8b with SMTP id d75a77b69052e-52df573954amr253830641cf.12.1787531388897; Sun, 23 Aug 2026 17:29:48 -0700 (PDT) Received: from rowland.harvard.edu ([2601:19b:d01:d210::dfd8]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-52e09ae7211sm36723671cf.26.2026.08.23.17.29.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 23 Aug 2026 17:29:47 -0700 (PDT) Date: Sun, 23 Aug 2026 20:29:45 -0400 From: Alan Stern To: Greg KH Cc: syzbot , dakr@kernel.org, driver-core@lists.linux.dev, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, rafael@kernel.org, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [usb?] INFO: task hung in unbind_store Message-ID: <190b86c3-5332-4d77-920c-a845f8a01b2c@rowland.harvard.edu> References: <6a8adc31.ae6ddae5.3da009.0064.GAE@google.com> <2026082307-negligent-lusty-750a@gregkh> <2ce6496d-6166-4470-b424-2b187908f2ba@rowland.harvard.edu> <2026082333-persuader-overturn-8205@gregkh> Precedence: bulk X-Mailing-List: linux-kernel@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: <2026082333-persuader-overturn-8205@gregkh> On Sun, Aug 23, 2026 at 07:28:10PM +0200, Greg KH wrote: > On Sun, Aug 23, 2026 at 10:40:03AM -0400, Alan Stern wrote: > > On Sun, Aug 23, 2026 at 01:46:43PM +0200, Greg KH wrote: > > > Ok, I'm going to add a new TAINT flag for when unbind is written to as > > > that is obviously not a normal operation and is only for debugging > > > things by kernel developers. Adding loads of work-arounds in the kernel > > > for this not-real-workload-path is just not required. > > > > > > If syzbot could stop hitting this path, that would be great, as it's a > > > root-only thing for debugging and not something "real". > > > > Actually, I could imagine people wanting to use unbind for a real > > purpose -- you could consider it to be a more specific form of modprobe > > blacklisting. > > If you want to do that, just don't load the module :) No, because unbinding is more precise. You can unbind a driver from one particular device. Not loading the module affects all the devices the driver might bind to. > > The bind attribute is the one which really should taint the kernel, > > because it bypasses the normal matching checks. Also, all the numerous > > syzbot bug reports coming out lately have involved weird bind > > operations, not unbind. Unbind should pretty much always work. > > "always work" is tough due to the races that can, and will, happen for > many non-hotplugged bus devices, as syzbot is finding now. We shouldn't > require this, as again, it's a debugging thing. If a driver does not support hotplugging, shouldn't it disable the bind and unbind attributes? (Is that possible? If not, it should be.) But if a driver does support hotplugging, unbinding it should definitely work every time. Alan Stern