linux-kernel - RE: [bug report] Commit ccf953d8f3d6 ("fb_defio: Remove custom address_space

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Date:   Fri, 4 Jun 2021 18:16:54 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Vineeth Pillai <viremana@...ux.microsoft.com>,
        Wei Liu <wei.liu@...nel.org>, vkuznets <vkuznets@...hat.com>
CC:     Matthew Wilcox <willy@...radead.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Kelley <mikelley@...rosoft.com>
Subject: RE: [bug report] Commit ccf953d8f3d6 ("fb_defio: Remove custom
 address_space_operations") breaks Hyper-V FB driver

> From: Vineeth Pillai <viremana@...ux.microsoft.com>
> Sent: Friday, June 4, 2021 8:47 AM
> To: Wei Liu <wei.liu@...nel.org>; vkuznets <vkuznets@...hat.com>
> Cc: Matthew Wilcox <willy@...radead.org>; dri-devel@...ts.freedesktop.org;
> linux-hyperv@...r.kernel.org; linux-fbdev@...r.kernel.org;
> linux-kernel@...r.kernel.org; Michael Kelley <mikelley@...rosoft.com>;
> Dexuan Cui <decui@...rosoft.com>
> Subject: Re: [bug report] Commit ccf953d8f3d6 ("fb_defio: Remove custom
> address_space_operations") breaks Hyper-V FB driver
> 
> 
> On 6/4/2021 9:00 AM, Wei Liu wrote:
> > On Fri, Jun 04, 2021 at 02:25:01PM +0200, Vitaly Kuznetsov wrote:
> >> Hi,
> >>
> >> Commit ccf953d8f3d6 ("fb_defio: Remove custom
> address_space_operations")
> >> seems to be breaking Hyper-V framebuffer
> >> (drivers/video/fbdev/hyperv_fb.c) driver for me: Hyper-V guest boots
> >> well and plymouth even works but when I try starting Gnome, virtual
> >> screen just goes black. Reverting the above mentioned commit on top of
> >> 5.13-rc4 saves the day. The behavior is 100% reproducible. I'm using
> >> Gen2 guest runing on Hyper-V 2019. It was also reported that Gen1 guests
> >> are equally broken.
> >>
> >> Is this something known?
> >>
> > I've heard a similar report from Vineeth but we didn't get to the bottom
> > of this.
> I have just tried reverting the commit mentioned above and it solves the
> GUI freeze
> I was also seeing. Previously, login screen was just freezing, but VM
> was accessible
> through ssh. With the above commit reverted, I can login to Gnome.
> 
> Looks like I am also experiencing the same bug mentioned here.
> 
> Thanks,
> Vineeth

As Matthew mentioned, this is a known issue:
https://lwn.net/ml/linux-kernel/YLZEhv0cpZp8uVE3@casper.infradead.org/

Matthew has reverted ccf953d8f3d6:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0b78f8bcf4951af30b0ae83ea4fad27d641ab617
so the latest mainline should work now.

Thanks,
Dexuan