[regression] opening and closing /dev/dri/card0 in a QEMU KVM instance will shutdown system

[Linux regression tracking (Thorsten Leemhuis)]

Hi, Thorsten here, the Linux kernel's regression tracker.

I noticed a report about a regression in bugzilla.kernel.org that
appears to be related to the simpledrm driver. As many (most?) kernel
developers don't keep an eye on the bug tracker, I decided to write this
mail. To quote from https://bugzilla.kernel.org/show_bug.cgi?id=219007 :

>  Colin Ian King 2024-07-05 16:05:27 UTC
> 
> The following code when run as root on a Debian sid amd64 server
> running in virt-manager (KVM QEMU) will shut the system down with
> 6.10.0-rc6.  The fork() is required to cause racing on the open/close on
> /dev/dri/card0
> 
> #include <fcntl.h>
> #include <unistd.h>
> 
> int main(void)
> {
> 	 pid_t pid = fork();
> 
> 	 while (1) {
> 	 	int fd;
> 
> 	 	fd = openat(AT_FDCWD, "/dev/dri/card0", O_WRONLY|O_NONBLOCK|O_SYNC);
> 	 	close(fd);
> 	 }
> }
> 
> This was originally found using: while true; do sudo ./stress-ng
> --dev 4 --dev-file /dev/dri/card0 -t 5; done and narrowed down to the
> above reproducer. (cf:
> https://github.com/ColinIanKing/stress-ng/issues/407 )
> 
> This does not occur on pre 6.10 kernels, so it looks like a 6.10 regression.

See the ticket for more details, which also contains a dmesg from a boot
in the VM: https://bugzilla.kernel.org/attachment.cgi?id=306610

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
Everything you wanna know about Linux kernel regression tracking:
https://linux-regtracking.leemhuis.info/about/#tldr
If I did something stupid, please tell me, as explained on that page.

P.S.: let me use this mail to also add the report to the list of tracked
regressions to ensure it's doesn't fall through the cracks:

#regzbot introduced: v6.9..v6.10
#regzbot title: drm: opening and closing /dev/dri/card0 in a QEMU KVM
instance will shutdown system
#regzbot from: Colin Ian King <colin.i.king at gmail.com>
#regzbot duplicate: https://bugzilla.kernel.org/show_bug.cgi?id=219007
#regzbot ignore-activity