linux-kernel - Re: possible deadlock in mon_bin_vma

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Message-ID: <20191120113314.761fce32@suzdal.zaitcev.lan>
Date:   Wed, 20 Nov 2019 11:33:14 -0600
From:   Pete Zaitcev <zaitcev@...hat.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     syzbot <syzbot+56f9673bb4cdcbeb0e92@...kaller.appspotmail.com>,
        arnd@...db.de, <gregkh@...uxfoundation.org>,
        <jrdr.linux@...il.com>, <keescook@...omium.org>,
        <kstewart@...uxfoundation.org>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>,
        <syzkaller-bugs@...glegroups.com>, <tglx@...utronix.de>,
        <viro@...iv.linux.org.uk>, zaitcev@...hat.com
Subject: Re: possible deadlock in mon_bin_vma_fault

On Wed, 20 Nov 2019 11:14:05 -0500 (EST)
Alan Stern <stern@...land.harvard.edu> wrote:

> As it happens, I spent a little time investigating this bug report just
> yesterday.  It seems to me that the easiest fix would be to disallow
> resizing the buffer while it is mapped by any users.  (Besides,
> allowing that seems like a bad idea in any case.)
> 
> Pete, does that seem reasonable to you?

Actually, please hold on a little, I think to think more about this.
The deadlock is between mon_bin_read and mon_bin_vma_fault.
To disallow resizing isn't going to fix _that_.

-- Pete