On Tue, 17 Sep 2019, syzbot wrote: > Hello, > > syzbot has tested the proposed patch but the reproducer still triggered > crash: > WARNING in sysfs_remove_group > > ------------[ cut here ]------------ > sysfs group 'power' not found for kobject 'radio3' > WARNING: CPU: 1 PID: 2883 at fs/sysfs/group.c:278 sysfs_remove_group > fs/sysfs/group.c:278 [inline] > WARNING: CPU: 1 PID: 2883 at fs/sysfs/group.c:278 > sysfs_remove_group+0x155/0x1b0 fs/sysfs/group.c:269 > Kernel panic - not syncing: panic_on_warn set ... > CPU: 1 PID: 2883 Comm: v4l_id Not tainted 5.3.0-rc7+ #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0xca/0x13e lib/dump_stack.c:113 > panic+0x2a3/0x6da kernel/panic.c:219 > __warn.cold+0x20/0x4a kernel/panic.c:576 > report_bug+0x262/0x2a0 lib/bug.c:186 > fixup_bug arch/x86/kernel/traps.c:179 [inline] > fixup_bug arch/x86/kernel/traps.c:174 [inline] > do_error_trap+0x12b/0x1e0 arch/x86/kernel/traps.c:272 > do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:291 > invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1028 > RIP: 0010:sysfs_remove_group fs/sysfs/group.c:278 [inline] > RIP: 0010:sysfs_remove_group+0x155/0x1b0 fs/sysfs/group.c:269 > Code: 48 89 d9 49 8b 14 24 48 b8 00 00 00 00 00 fc ff df 48 c1 e9 03 80 3c > 01 00 75 41 48 8b 33 48 c7 c7 e0 c8 d0 85 e8 a0 0e 8b ff <0f> 0b eb 95 e8 > e2 d1 db ff e9 d2 fe ff ff 48 89 df e8 d5 d1 db ff > RSP: 0018:ffff8881c6d17c50 EFLAGS: 00010286 > RAX: 0000000000000000 RBX: ffffffff85f2d700 RCX: 0000000000000000 > RDX: 0000000000000000 RSI: ffffffff81288ddd RDI: ffffed1038da2f7c > RBP: 0000000000000000 R08: ffff8881d6243000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000000 R12: ffff8881cf014cd8 > R13: ffffffff85f2dca0 R14: 0000000000000000 R15: ffff8881cf015178 > dpm_sysfs_remove+0x97/0xb0 drivers/base/power/sysfs.c:735 > device_del+0x12a/0xb10 drivers/base/core.c:2316 > device_unregister+0x11/0x30 drivers/base/core.c:2371 > video_unregister_device+0xa2/0xc0 drivers/media/v4l2-core/v4l2-dev.c:1051 > usbvision_unregister_video+0x83/0x120 > drivers/media/usb/usbvision/usbvision-video.c:1243 > usbvision_release+0x10d/0x1c0 > drivers/media/usb/usbvision/usbvision-video.c:1356 > usbvision_radio_close.cold+0x2b/0x74 > drivers/media/usb/usbvision/usbvision-video.c:1129 > v4l2_release+0x2e7/0x390 drivers/media/v4l2-core/v4l2-dev.c:455 > __fput+0x2d7/0x840 fs/file_table.c:280 > task_work_run+0x13f/0x1c0 kernel/task_work.c:113 > tracehook_notify_resume include/linux/tracehook.h:188 [inline] > exit_to_usermode_loop+0x1d2/0x200 arch/x86/entry/common.c:163 > prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline] > syscall_return_slowpath arch/x86/entry/common.c:274 [inline] > do_syscall_64+0x45f/0x580 arch/x86/entry/common.c:299 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x7f4fde8992b0 > Code: 40 75 0b 31 c0 48 83 c4 08 e9 0c ff ff ff 48 8d 3d c5 32 08 00 e8 c0 > 07 02 00 83 3d 45 a3 2b 00 00 75 10 b8 03 00 00 00 0f 05 <48> 3d 01 f0 ff > ff 73 31 c3 48 83 ec 08 e8 ce 8a 01 00 48 89 04 24 > RSP: 002b:00007ffcce3d65f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000003 > RAX: 0000000000000000 RBX: 0000000000000003 RCX: 00007f4fde8992b0 > RDX: 0000000000000013 RSI: 0000000080685600 RDI: 0000000000000003 > RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000400884 > R13: 00007ffcce3d6750 R14: 0000000000000000 R15: 0000000000000000 > Kernel Offset: disabled > Rebooting in 86400 seconds.. > > > Tested on: > > commit: f0df5c1b usb-fuzzer: main usb gadget fuzzer driver > git tree: https://github.com/google/kasan.git > console output: https://syzkaller.appspot.com/x/log.txt?x=178ba88d600000 > kernel config: https://syzkaller.appspot.com/x/.config?x=5c6633fa4ed00be5 > dashboard link: https://syzkaller.appspot.com/bug?extid=7fa38a608b1075dfd634 > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > patch: https://syzkaller.appspot.com/x/patch.diff?x=14ce1b59600000 This is more than I can fix. The whole way the v4l2 layer handles reference counting seems suspicious and I don't understand it. (Does the code assume that the only reference holders are initial registration and open files?) In this case it looks like the device may be unregistered twice. It's hard to tell exactly what's going wrong without knowing more about how this is supposed to work. It wouldn't hurt, for example, to use dev_info() instead of printk(KERN_INFO) in places like usbvision_disconnect(). I'm going to step back and let the maintainers deal with the rest of this. Alan Stern
