linux-kernel - Re: [syzbot] INFO: task hung in r871xu_dev

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Date:   Thu, 9 Dec 2021 21:22:29 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     syzbot <syzbot+f39c1dad0b7db49ca4a8@...kaller.appspotmail.com>,
        Larry.Finger@...inger.net, florian.c.schilhabel@...glemail.com,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        linux-staging@...ts.linux.dev, linux-usb@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] INFO: task hung in r871xu_dev_remove

On 12/9/21 09:27, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    d598c3c46ea6 Merge 5.16-rc4 into usb-next
> git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing
> console output: https://syzkaller.appspot.com/x/log.txt?x=14cf0e55b00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c6df5f09a0b9c823
> dashboard link: https://syzkaller.appspot.com/bug?extid=f39c1dad0b7db49ca4a8
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+f39c1dad0b7db49ca4a8@...kaller.appspotmail.com
> 
> INFO: task kworker/0:6:4133 blocked for more than 143 seconds.
>        Not tainted 5.16.0-rc4-syzkaller #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:kworker/0:6     state:D stack:21848 pid: 4133 ppid:     2 flags:0x00004000
> Workqueue: usb_hub_wq hub_event
> Call Trace:
>   <TASK>
>   context_switch kernel/sched/core.c:4972 [inline]
>   __schedule+0x931/0x2320 kernel/sched/core.c:6253
>   schedule+0xd2/0x260 kernel/sched/core.c:6326
>   schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6385
>   __mutex_lock_common kernel/locking/mutex.c:680 [inline]
>   __mutex_lock+0xa32/0x12f0 kernel/locking/mutex.c:740
>   unregister_netdev+0xe/0x20 net/core/dev.c:11138
>   r871xu_dev_remove+0x24f/0x2c0 drivers/staging/rtl8712/usb_intf.c:599

Seems like syz-executor ddosed the kernel. unregister_netdev() tries to 
lock rtnl and there are 8 mentions of rtnl_mutex in "Showing all locks 
held in the system" section.

Looks false-positive to me




With regards,
Pavel Skripkin