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Date:   Sun, 24 Jan 2021 12:06:54 -0800 (PST)
From:   Hugh Dickins <hughd@google.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
cc:     Hugh Dickins <hughd@google.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Stephan Gerhold <stephan@gerhold.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Chen <Peter.Chen@nxp.com>,
        Kishon Vijay Abraham I <kishon@ti.com>,
        "open list:ULTRA-WIDEBAND (UWB) SUBSYSTEM:" 
        <linux-usb@vger.kernel.org>, Thierry Reding <treding@nvidia.com>,
        Saravana Kannan <saravanak@google.com>,
        linux-pm@vger.kernel.org
Subject: Re: Infinite recursion in device_reorder_to_tail() due to circular
 device links
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On Sun, 24 Jan 2021, Greg Kroah-Hartman wrote:
> On Sat, Jan 23, 2021 at 03:37:30PM -0800, Hugh Dickins wrote:
> > On Tue, 12 Jan 2021, Greg Kroah-Hartman wrote:
> > > On Tue, Jan 12, 2021 at 03:32:04PM +0100, Rafael J. Wysocki wrote:
> > > > On Mon, Jan 11, 2021 at 7:46 PM Stephan Gerhold <stephan@gerhold.net> wrote:
> > > > >
> > > > > Hi,
> > > > >
> > > > > since 5.11-rc1 I get kernel crashes with infinite recursion in
> > > > > device_reorder_to_tail() in some situations... It's a bit complicated to
> > > > > explain so I want to apologize in advance for the long mail. :)
> > > > >
> > > > >   Kernel panic - not syncing: kernel stack overflow
> > > > >   CPU: 1 PID: 33 Comm: kworker/1:1 Not tainted 5.11.0-rc3 #1
> > > > >   Hardware name: Qualcomm Technologies, Inc. APQ 8016 SBC (DT)
> > > > >   Call trace:
> > > > >    ...
> > > > >    device_reorder_to_tail+0x4c/0xf0
> > > > >    device_reorder_to_tail+0x98/0xf0
> > > > >    device_reorder_to_tail+0x60/0xf0
> > > > >    device_reorder_to_tail+0x60/0xf0
> > > > >    device_reorder_to_tail+0x60/0xf0
> > > > >    ...
> > > > >
> > > > > The crash happens only in 5.11 with commit 5b6164d3465f ("driver core:
> > > > > Reorder devices on successful probe"). It stops happening when I revert
> > > > > this commit.
> > > > 
> > > > Thanks for the report!
> > > > 
> > > > Greg, please revert commit 5b6164d3465f, it clearly is not an
> > > > improvement, at least at this point.
> > > 
> > > Now reverted, thanks.
> > > 
> > > greg k-h
> > 
> > I think that there has been a misunderstanding here: although
> > 5b6164d3465f ("driver core: Reorder devices on successful probe")
> > has been reverted from linux-next (thank you), it has not yet been
> > reverted from 5.11-rc, and still causing problems there (in my case,
> > not the infinite recursion Stephan reported in this thread, but the
> > ThinkPad rmi4 suspend failure that I reported in another thread).
> 
> It will be sent to Linus in a few hours, thanks, so should show up in
> 5.11-rc5.  I had other patches to go along with this to send him at the
> same time :)

And indeed it's now in, thanks Greg: I'm sorry for being importunate,
the misunderstanding was mine.

Hugh