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smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=kvh+riaE; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="kvh+riaE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 787561F000E9; Sun, 23 Aug 2026 17:29:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1787506190; bh=s/X4uoXU1lSsTreDd4JtMNx12If+u9/RDGV3FNS1Sf0=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=kvh+riaE8ySP8Sxq6Bnm0tgug2Dnral/1xux4lVSi8SpNWlha1TTyIWZ4d8gfjB2+ PFlPQECbSReptY31ls86nTuvE8507LN3tjCUyrYeqiQI0WYgXqZj0dFbyXl5U2bgVW 6FSknV/FAM1rKNKxGrVqHlCH9JdP6fjhP4Nv49K0= Date: Sun, 23 Aug 2026 19:28:10 +0200 From: Greg KH To: Alan Stern 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: <2026082333-persuader-overturn-8205@gregkh> References: <6a8adc31.ae6ddae5.3da009.0064.GAE@google.com> <2026082307-negligent-lusty-750a@gregkh> <2ce6496d-6166-4470-b424-2b187908f2ba@rowland.harvard.edu> 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: <2ce6496d-6166-4470-b424-2b187908f2ba@rowland.harvard.edu> 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: > > On Sun, Aug 23, 2026 at 04:40:33AM -0700, syzbot wrote: > > > Hello, > > > > > > syzbot found the following issue on: > > > > > > HEAD commit: e8bf40d15402 Merge tag 'chrome-platform-firmware-v7.3' of .. > > > git tree: upstream > > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=13e9f679580000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=1941312e3e971b07 > > > dashboard link: https://syzkaller.appspot.com/bug?extid=fd7be5ad9795b7f29df3 > > > compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8 > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14a75679580000 > > > > > > Downloadable assets: > > > disk image: https://storage.googleapis.com/syzbot-assets/7df7b958efe0/disk-e8bf40d1.raw.xz > > > vmlinux: https://storage.googleapis.com/syzbot-assets/cefbf90e524a/vmlinux-e8bf40d1.xz > > > kernel image: https://storage.googleapis.com/syzbot-assets/37a530b91001/bzImage-e8bf40d1.xz > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > > Reported-by: syzbot+fd7be5ad9795b7f29df3@syzkaller.appspotmail.com > > > > > > 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". > > 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 :) > 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. bind is used by the virtio people for some reason, but yes, I will be glad to taint at that point as well. I'll look into doing that after -rc1 is out. thanks, greg k-h