Hi Geert,
IMHO - QEMU is irrelevant here. since I can do passthrough --
in fact -- many drivers do use timeout in .fb_sync
e.g. i810fb_sync(), nouveau_fbcon_sync(), sm501fb_sync() etc..
I believe the correct behaviour should be a timeout wait instead of
waiting indefinitely.
- Tong

On Wed, Feb 24, 2021 at 6:35 AM Geert Uytterhoeven [off-list ref] wrote:

Hi Tong,

On Sun, Feb 21, 2021 at 1:05 AM Tong Zhang [off-list ref] wrote:

quoted

On Sat, Feb 20, 2021 at 6:33 PM Randy Dunlap [off-list ref] wrote:

quoted

On 2/20/21 3:02 PM, Tong Zhang wrote:

quoted

pm2fb_sync is called when doing /dev/fb read or write.
The original pm2fb_sync wait indefinitely on hardware flags which can
possibly stall kernel and make everything unresponsive.
Instead of waiting indefinitely, we can timeout to give user a chance to
get back control.

Is this a real problem or theoretical?
Does someone still use this driver?

I currently have this problem on my machine.
I have submitted a revised patch -- which includes the console log.

Your machine is "QEMU Standard"?
Can this happen on real hardware, too, or is this a deficiency in QEMU,
which should be fixed there?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds