Re: [PATCH] char: misc: make misc_open() and misc_register() killable

Greg KH
2022-07-05T05:37:33Z

On Tue, Jul 05, 2022 at 02:21:17PM +0900, Tetsuo Handa wrote:
> On 2022/07/04 23:31, Greg KH wrote:
> > I don't understand what you are trying to "fix" here. What is userspace
> > doing (as a normal user) that is causing a problem, and what problem is
> > it causing and for what device/hardware/driver is this a problem?
>
> Currently the root cause is unknown.
> This might be another example of deadlock hidden by device_initialize().
>
> We can see from https://syzkaller.appspot.com/text?tag=CrashReport&x=11feb7e0080000 that
> when khungtaskd reports that a process is blocked waiting for misc_mtx at misc_open(),
> there is a process which is holding system_transition_mutex from snapshot_open().

/dev/snapshot is not read/writable by anyone but root for obvious
reasons.

And perhaps it's something that syzbot shouldn't be fuzzing unless it
wants to take the system down easily :)

thanks,

greg k-h