From: Pete Zaitcev <zaitcev@redhat.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: syzbot <syzbot+56f9673bb4cdcbeb0e92@syzkaller.appspotmail.com>,
<arnd@arndb.de>, <gregkh@linuxfoundation.org>,
<jrdr.linux@gmail.com>, <keescook@chromium.org>,
<kstewart@linuxfoundation.org>,
Kernel development list <linux-kernel@vger.kernel.org>,
USB list <linux-usb@vger.kernel.org>,
<syzkaller-bugs@googlegroups.com>, <tglx@linutronix.de>,
<viro@zeniv.linux.org.uk>,
zaitcev@redhat.com
Subject: Re: possible deadlock in mon_bin_vma_fault
Date: Thu, 21 Nov 2019 08:48:42 -0600 [thread overview]
Message-ID: <20191121084842.095edf87@suzdal.zaitcev.lan> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1911201343580.1498-100000@iolanthe.rowland.org>
On Wed, 20 Nov 2019 13:47:00 -0500 (EST)
Alan Stern <stern@rowland.harvard.edu> wrote:
> > + if (rp->mmap_active)
> > + return -EBUSY;
> Like that, yes, but the test has to be made while fetch_lock is held.
Certainly, thanks. I was rushing just to add a postscriptum.
> Incidentally, the comment for fetch_lock says that it protects b_read
> and b_out, but mon_bin_vma_fault doesn't use either of those fields.
I probably should change that comment to "protect the integrity of the
circular buffer, such as b_out".
Anyway... If you are looking at it too, what do you think about not using
any locks in mon_bin_vma_fault() at all? Isn't it valid? I think I tried
to be "safe", but it only uses things that are constants unless we're
opening and closing; a process cannot make page faults unless it has
some thing mapped; and that is only possible if device is open and stays
open. Can you find a hole in this reasoning?
-- Pete
next prev parent reply other threads:[~2019-11-21 14:48 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <0000000000006ad6030574fead2e@google.com>
2019-11-20 12:01 ` possible deadlock in mon_bin_vma_fault syzbot
2019-11-20 16:14 ` Alan Stern
2019-11-20 17:12 ` Pete Zaitcev
2019-11-20 18:47 ` Alan Stern
2019-11-21 14:48 ` Pete Zaitcev [this message]
2019-11-21 16:20 ` Alan Stern
2019-11-21 16:46 ` Pete Zaitcev
2019-11-21 23:38 ` Pete Zaitcev
2019-11-22 7:18 ` Dmitry Vyukov
2019-11-22 15:27 ` Alan Stern
2019-11-22 20:52 ` Pete Zaitcev
2019-11-22 22:13 ` Alan Stern
2019-11-22 22:13 ` syzbot
2019-11-23 17:18 ` Alan Stern
2019-11-23 17:18 ` syzbot
2019-11-24 15:59 ` Alan Stern
2019-11-24 19:10 ` syzbot
2019-11-24 20:55 ` Alan Stern
2019-11-24 23:24 ` syzbot
2019-11-25 0:10 ` Pete Zaitcev
2019-11-25 2:12 ` Alan Stern
2019-11-23 17:18 ` Re: " syzbot
2019-11-22 22:13 ` syzbot
2019-11-20 17:33 ` Pete Zaitcev
2019-11-20 18:18 ` Alan Stern
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