Re: [PATCH 4.4 00/37] 4.4.110-stable review

[Andy Lutomirski]

> On Jan 4, 2018, at 12:29 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> 
>> On Thu, Jan 4, 2018 at 12:16 PM, Thomas Voegtle <tv@xxxxxxxx> wrote:
>> 
>> Attached a screenshot.
>> Is that useful? Are there some debug options I can add?
> 
> Not much of an oops, because the SIGSEGV happens in user space. The
> only reason you get any kernel stack printout at all is because 'init'
> dying will make the kernel print that out.
> 
> The segfault address for init looks like the fixmap area to me (first
> byte in the last page of the fixmap?). "Error 5" means that it's a
> user-space read that got a protection fault. So it's not a LDT of GDT
> update or anything like that, it's a normal access from user space (or
> a qemu emulation bug, but that sounds unlikely).
> 
> Is that the vsyscall page?
> 
> Adding Luto to the participants. I think he noticed one of the
> vsyscall patches missing earlier in the 4.9 series. Maybe the 4.4
> series had something similar..
> 

That's almost certainly it.

I'll try to find some time today or tomorrow to add a proper selftest.

>              Linus