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Message-ID: <1597231141.28022.7.camel@suse.com>
Subject: Re: [PATCH] USB: cdc-wdm: Remove unsafe wdm_flush().
From:   Oliver Neukum <oneukum@suse.com>
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Colin Ian King <colin.king@canonical.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-usb@vger.kernel.org,
        syzbot <syzbot+854768b99f19e89d7f81@syzkaller.appspotmail.com>
Date:   Wed, 12 Aug 2020 13:19:01 +0200
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Am Mittwoch, den 12.08.2020, 19:09 +0900 schrieb Tetsuo Handa:
> On 2020/08/12 17:02, Oliver Neukum wrote:
> > Am Mittwoch, den 12.08.2020, 08:26 +0900 schrieb Tetsuo Handa:
> > > syzbot is reporting hung task at wdm_flush() [1], for there is a circular
> > > dependency that wdm_flush() from flip_close() for /dev/cdc-wdm0 forever
> > > waits for /dev/raw-gadget to be closed while close() for /dev/raw-gadget
> > > cannot be called unless close() for /dev/cdc-wdm0 completes.
> > > 
> > > It turned out that wdm_flush() is broken in multiple aspects.
> > 
> > Sorry,
> > 
> > this seems to be a miscommunication. I was under the impression that
> > you were testing patches. I will push them upstream. You
> > cannot just remove flush() without impairing error handling.
> 
> Then, will you check
> 
>   https://lore.kernel.org/linux-usb/254939d4-f3a1-8c7e-94e5-9862c02774fa@i-love.sakura.ne.jp/
> 
> and
> 
>   https://lore.kernel.org/linux-usb/c85331fc-874c-6e46-a77f-0ef1dc075308@i-love.sakura.ne.jp/
> 
> before pushing upstream?

Hi,

sure, yes, thank you for the pointers. I shall post an RFC in a few
minutes.

	Regards
		Oliver