Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 30 Apr 2019 15:34:12 -0400 (EDT)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Mike Isely <isely@pobox.com>,
        syzbot <syzbot+170a86bf206dd2c6217e@syzkaller.appspotmail.com>
cc:     andreyknvl@google.com, <linux-media@vger.kernel.org>,
        Kernel development list <linux-kernel@vger.kernel.org>,
        USB list <linux-usb@vger.kernel.org>,
        <syzkaller-bugs@googlegroups.com>
Subject: Re: WARNING: Detected a wedged cx25840 chip; the device will not
 work.
In-Reply-To: <000000000000b7a84a0587c3f3e5@google.com>
Message-ID: <Pine.LNX.4.44L0.1904301530070.1465-100000@iolanthe.rowland.org>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, 30 Apr 2019, syzbot wrote:

> Hello,
> 
> syzbot has tested the proposed patch but the reproducer still triggered  
> crash:
> WARNING in sysfs_remove_group
> 
> pvrusb2: Attached sub-driver tuner
> pvrusb2: ***WARNING*** pvrusb2 driver initialization failed due to the  
> failure of one or more sub-device kernel modules.
> pvrusb2: You need to resolve the failing condition before this driver can  
> function.  There should be some earlier messages giving more information  
> about the problem.
> ------------[ cut here ]------------
> sysfs group 'power' not found for kobject '0-0044'
> WARNING: CPU: 1 PID: 586 at fs/sysfs/group.c:254 sysfs_remove_group  
> fs/sysfs/group.c:254 [inline]
> WARNING: CPU: 1 PID: 586 at fs/sysfs/group.c:254  
> sysfs_remove_group+0x15a/0x1b0 fs/sysfs/group.c:245
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 1 PID: 586 Comm: pvrusb2-context Not tainted 5.1.0-rc3-g43151d6-dirty  
> #1
> 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+0xe8/0x16e lib/dump_stack.c:113
>   panic+0x29d/0x5f2 kernel/panic.c:214
>   __warn.cold+0x20/0x48 kernel/panic.c:571
>   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+0x130/0x1f0 arch/x86/kernel/traps.c:272
>   do_invalid_op+0x37/0x40 arch/x86/kernel/traps.c:291
>   invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
> RIP: 0010:sysfs_remove_group fs/sysfs/group.c:254 [inline]
> RIP: 0010:sysfs_remove_group+0x15a/0x1b0 fs/sysfs/group.c:245
> 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 a0 31 7a 8e e8 e6 c2 6e ff <0f> 0b eb 95 e8  
> 0d de d3 ff e9 d2 fe ff ff 48 89 df e8 00 de d3 ff
> RSP: 0018:ffff88809ced7b70 EFLAGS: 00010286
> RAX: 0000000000000000 RBX: ffffffff8f037e80 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffffffff815b2132 RDI: ffffed10139daf60
> RBP: 0000000000000000 R08: ffff88809ce96200 R09: ffffed1015a23edb
> R10: ffffed1015a23eda R11: ffff8880ad11f6d7 R12: ffff888218b8e630
> R13: ffffffff8f038520 R14: 1ffff110139daf97 R15: ffff888218b8e628
>   dpm_sysfs_remove+0xa2/0xc0 drivers/base/power/sysfs.c:737
>   device_del+0x175/0xb90 drivers/base/core.c:2246
> usb 4-1: new high-speed USB device number 3 using dummy_hcd
>   device_unregister+0x27/0xd0 drivers/base/core.c:2301
>   i2c_unregister_device drivers/i2c/i2c-core-base.c:814 [inline]
>   __unregister_client drivers/i2c/i2c-core-base.c:1422 [inline]
>   __unregister_client+0x7d/0x90 drivers/i2c/i2c-core-base.c:1418
>   device_for_each_child+0x100/0x170 drivers/base/core.c:2401
>   i2c_del_adapter drivers/i2c/i2c-core-base.c:1485 [inline]
>   i2c_del_adapter+0x35b/0x640 drivers/i2c/i2c-core-base.c:1447
>   pvr2_i2c_core_done+0x6e/0xbb  
> drivers/media/usb/pvrusb2/pvrusb2-i2c-core.c:662
>   pvr2_hdw_destroy+0x17e/0x380 drivers/media/usb/pvrusb2/pvrusb2-hdw.c:2669
>   pvr2_context_destroy+0x89/0x240  
> drivers/media/usb/pvrusb2/pvrusb2-context.c:79
>   pvr2_context_check drivers/media/usb/pvrusb2/pvrusb2-context.c:146 [inline]
>   pvr2_context_thread_func+0x65e/0x870  
> drivers/media/usb/pvrusb2/pvrusb2-context.c:167
>   kthread+0x313/0x420 kernel/kthread.c:253
>   ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
> 
> 
> Tested on:
> 
> commit:         43151d6c usb-fuzzer: main usb gadget fuzzer driver
> git tree:       https://github.com/google/kasan.git usb-fuzzer
> console output: https://syzkaller.appspot.com/x/log.txt?x=15433634a00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=274aad0cf966c3bc
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> patch:          https://syzkaller.appspot.com/x/patch.diff?x=13df3d24a00000

It seems pretty clear that this problem is caused by the
pvr2_context_thread trying to unregister the device before the main
probe routine has finished registering it.

I'm not familiar enough with this driver to want to fix the problem, 
however.  Someone else who knows the code better should work on it.

Alan Stern