From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f51.google.com (mail-wm1-f51.google.com [209.85.128.51]) (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 0BF1640E8D7 for ; Thu, 27 Aug 2026 09:00:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.51 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787821216; cv=none; b=X5yXITNXZpUSAJoKy1Upc31DCPdf3uRf5XtB9/zp+QcvOa20PhVrnvodOFnxoWomhHnNJLownfP/lrQ8dAiVqUPNmxY6ri8S6CytX1SmAy6FI2k4+tyhh5j2tCKbuDpCeNmQNgTO6yntCKF9NrmUp+YqHOvKgWGuiOKQ3cj5/9g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787821216; c=relaxed/simple; bh=ULL0WSE+VnO9meH9P9SHFZ/5ECm8VRmPNFjsu7sTbZw=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=hKib7J3x1R4Q264j5VWFCuttqf1A9+BnvWVCstikG5iS7BZEsjmjkSLb7TQFLWa/4xOxK4dQt8QcqXK2q2SwZQDNfUkNqsXkP5dVV8zdNRd0F3tx+DpxFKRH6MvBuh1W9r85lbCy4hhDfhJg3k3UHjdvlSzZEZei6M9SRqcaYrY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=jeE/EgOm; arc=none smtp.client-ip=209.85.128.51 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="jeE/EgOm" Received: by mail-wm1-f51.google.com with SMTP id 5b1f17b1804b1-49b8e527d63so2386645e9.2 for ; Thu, 27 Aug 2026 02:00:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1787821211; x=1788426011; darn=vger.kernel.org; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=Cm05Jqi50ugmia6yOpX5uH7qKzSDAmXg4hbuH3KqhN8=; b=jeE/EgOmL/BsZ3fQtM3srvFZs9GDjvtJzuAJL4DfKzQ7jmjU4Tmi/En8bjSK+bAUpb v+Q4WT4u0I7asMLTG4TsxKLq5WY5aCuMFKcyDoDQ3FhPKI+VvBdKI9h12ogS9rrLIFXW 2a9y5UOIN9qLRhvlVHbcaNIsKGs01AR9mCC0IobJdu+EUaRbRK+qKUiQdnrC04Ma0u2k 1bwznLwKRKoDnU5BZTkE/o7m5goS3FbVFfzANj9mVuzEUFd3KYUAR8biaJJLqQSlKh/w Qg1hwfHEZidnX4l8RFcdsNdPxIJGHH9itPGw5h8VkRQEDePousvxQMEK78vGgSB2/QS2 rEDA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1787821211; x=1788426011; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to: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=Cm05Jqi50ugmia6yOpX5uH7qKzSDAmXg4hbuH3KqhN8=; b=i+2g2aiLwVXDYLFVYXMu5bdj+WMskH+V3+WZjCrEoZsvPLA1WFd/KVjaFTVYHg7v/f 6yLnzj/4ySe3zDBSLdzVjf2qHtPotIIZAf4S+yddj9KnmbyRj1fZIXnHy1UcahF2zZt2 If4GxtCQoDoAwur0aSe/F3YH87TVJ7vWLZGOxSBpchu45HIRpeCwI1Pqh/sTgNkkIwr1 c85n7BaVTFhfNfCdquNoZMH8R9e8raT0zBfDM+NqqZhbnp6PKsB63gbN2jDg00sV3lxG 5OgaUdqAt732nsBCePtQyZNY5xQNuvkTtBtjRy+UXf9xsE4ihTvYmNufkI8ogRf3UnVz nmdw== X-Forwarded-Encrypted: i=1; AHgh+RrFmUJl7Am23fFa5Cugls2ECDzpmGSV99y9U0Eg1rYsweQavPTXBM/bILyIJEZ8NJ0scFx/u2OGcv9/MBU=@vger.kernel.org X-Gm-Message-State: AFuF++m7VPdh1b0/q6svZyAyJcwLaYYEWPADesvXwu2uyvt09GalgAoC 5GpTZyimZPHubGNOeoyvfMppxfw/5XyTu/53vR12iX2WN3tWmShEkiA7 X-Gm-Gg: AR+sD113AT9+Q9NwP+er5qoDoMRw5wbti4SBrGmw0lugidVM8daN5VN57jML54oy6EF hKJxQ8FORsbDxfAkXJPs8O5WeAjc/S15ak/mf9wUS3Cn+9hcoFwWy9u4rMhW6r3zSx+mQXbZsIj kX1RVAmBwxdK4xQEzkm4RGCBT6Qyl+BvJRxzMm7Eh0AS9nohLYQEZ7tkhs6w2UuVsQ+jC1eKIx3 7aF4EtlaOp7q8LDZijp8lYRvwmetTv5S0XoYBB1o5QlhhUclaIYrpPOP0o+mMim20mt3TEuigGm xgyjncEBs1q25MrcCtw5I+mawvwTvws4fCnhtKpRcTuSGGFWrb9vTy+Mmj2Ky3SoQMd7t1STFjp cx/fDH6OJu+XTTqDFb+tpBfqOh3JI/ABIP+qIvt3e3tTMPQkprkXNnHbBMuZOy2IKVv7XiNHKIk of5zrJm1D3779jZtjGsDnOVPTEzyepz+VCoLSFZQiCeccmuKEDakj9AkrrlQZIHmflfBE= X-Received: by 2002:a05:600c:3b0c:b0:499:b01e:911c with SMTP id 5b1f17b1804b1-499dc6ea9f4mr154197375e9.2.1787821210834; Thu, 27 Aug 2026 02:00:10 -0700 (PDT) Received: from foxbook (bfk5.neoplus.adsl.tpnet.pl. [83.28.48.5]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-499dd56dfb8sm51305175e9.3.2026.08.27.02.00.09 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Thu, 27 Aug 2026 02:00:10 -0700 (PDT) Date: Thu, 27 Aug 2026 11:00:06 +0200 From: Michal Pecio 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: <20260827110006.66b07ea4.michal.pecio@gmail.com> In-Reply-To: <2026082307-negligent-lusty-750a@gregkh> References: <6a8adc31.ae6ddae5.3da009.0064.GAE@google.com> <2026082307-negligent-lusty-750a@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-Transfer-Encoding: 7bit On Sun, 23 Aug 2026 13:46:43 +0200, Greg KH wrote: > On Sun, Aug 23, 2026 at 04:40:33AM -0700, syzbot wrote: > > INFO: task syz.4.23:6285 blocked for more than 143 seconds. > > Not tainted syzkaller #0 > > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > > task:syz.4.23 state:D stack:27592 pid:6285 tgid:6285 ppid:6213 task_flags:0x400140 flags:0x00080002 > > Call Trace: > > > > context_switch kernel/sched/core.c:5510 [inline] > > __schedule+0x17d4/0x5630 kernel/sched/core.c:7239 > > __schedule_loop kernel/sched/core.c:7316 [inline] > > schedule+0x164/0x2b0 kernel/sched/core.c:7331 > > schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7388 > > __mutex_lock_common kernel/locking/mutex.c:726 [inline] > > __mutex_lock+0x7c1/0x1550 kernel/locking/mutex.c:821 > > device_lock include/linux/device.h:1104 [inline] > > __device_driver_lock drivers/base/dd.c:1170 [inline] > > device_release_driver_internal+0x93/0x880 drivers/base/dd.c:1369 > > unbind_store+0x1a1/0x1d0 drivers/base/bus.c:244 > > 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". The root cause is probe() call of one USB driver (sisusbvga) taking an eternity to complete on nonresponsive hardware, which is actually a pretty real and not so uncommon annoying behavior. And something is also wrong with those timeouts, because 20 times 5s should still be less than 143 s. I asked Syzbot to try 500ms instead, which ended up being over 3s in practice: [ 566.662036][ T6636] usb 4-1: sisusb_send_bulk_msg() [ 569.717341][ T6636] usb 4-1: sisusb_send_bulk_msg() [ 572.777761][ T6636] usb 4-1: sisusb_send_bulk_msg() [ 575.845365][ T6636] usb 4-1: sisusb_send_bulk_msg() Same on my system, but patch below reduces the timeout to 500ms. I have no idea what's happening here. Looks like a bug? Is it known that jiffies are totally unreliable like that? Regards, Michal --- a/drivers/usb/misc/sisusbvga/sisusbvga.c +++ b/drivers/usb/misc/sisusbvga/sisusbvga.c @@ -225,9 +225,13 @@ static int sisusb_bulkout_msg(struct sisusb_usb_data *sisusb, int index, /* If OK, and if timeout > 0, wait for completion */ if ((retval == 0) && timeout) { + u64 time = ktime_get_ns(); + wait_event_timeout(sisusb->wait_q, (!(sisusb->urbstatus[index] & SU_URB_BUSY)), timeout); + dev_info(&sisusb->sisusb_dev->dev, "sisusb_bulkout_msg() waited %lld\n", ktime_get_ns() - time); + if (sisusb->urbstatus[index] & SU_URB_BUSY) { /* URB timed out... kill it and report error */ usb_kill_urb(urb);