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Date:   Fri, 9 Aug 2019 15:32:51 -0400 (EDT)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     syzbot <syzbot+a64a382964bf6c71a9c0@syzkaller.appspotmail.com>
cc:     andreyknvl@google.com, <gregkh@linuxfoundation.org>,
        <linux-kernel@vger.kernel.org>, <linux-usb@vger.kernel.org>,
        <oneukum@suse.de>, <syzkaller-bugs@googlegroups.com>
Subject: Re: possible deadlock in usb_deregister_dev
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On Fri, 9 Aug 2019, syzbot wrote:

> syzbot has found a reproducer for the following crash on:
> 
> HEAD commit:    e96407b4 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=15bf780e600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=cfa2c18fb6a8068e
> dashboard link: https://syzkaller.appspot.com/bug?extid=a64a382964bf6c71a9c0
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16787574600000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=136cc4d2600000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+a64a382964bf6c71a9c0@syzkaller.appspotmail.com
> 
> usb 1-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
> usb 1-1: config 0 descriptor??
> iowarrior 1-1:0.236: IOWarrior product=0x1501, serial= interface=236 now  
> attached to iowarrior0
> usb 1-1: USB disconnect, device number 2
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.3.0-rc2+ #25 Not tainted
> ------------------------------------------------------
> kworker/0:1/12 is trying to acquire lock:
> 00000000cd63e8f1 (minor_rwsem){++++}, at: usb_deregister_dev  
> drivers/usb/core/file.c:238 [inline]
> 00000000cd63e8f1 (minor_rwsem){++++}, at: usb_deregister_dev+0x61/0x270  
> drivers/usb/core/file.c:230
> 
> but task is already holding lock:
> 000000001d1989ef (iowarrior_open_disc_lock){+.+.}, at:  
> iowarrior_disconnect+0x45/0x2c0 drivers/usb/misc/iowarrior.c:867
> 
> which lock already depends on the new lock.

https://syzkaller.appspot.com/bug?extid=ca52394faa436d8131df is 
undoubtedly a duplicate of this.

Alan Stern