Re: [BUG] kernel BUG at mm/vmacache.c:85!

[Hugh Dickins <hughd@google.com>]

On Mon, 28 Apr 2014, Linus Torvalds wrote:
> On Mon, Apr 28, 2014 at 2:20 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > That said, the bug does seem to be that some path doesn't invalidate
> > the vmacache sufficiently, or something inserts a vmacache entry into
> > the current process when looking up a remote process or whatever.
> > Davidlohr, ideas?
> 
> Maybe we missed some use_mm() call. That will change the current mm
> without flushing the vma cache. The code considers kernel threads to
> be bad targets for vma caching for this reason (and perhaps others),
> but maybe we missed something.
> 
> I wonder if we should just invalidate the vma cache in use_mm(), and
> remote the "kernel tasks are special" check.
> 
> Srivatsa, are you doing something peculiar on that system that would
> trigger this? I see some kdump failures in the log, anything else?

I doubt that the vmacache has anything to do with the real problem
(though it *might* suggest that vmacache is less robust than what
it replaced - maybe).  The log is so full of userspace SIGSEGVs
and General Protection faults, it looks like userspace was utterly
broken by some kernel bug messing up the address space.

Hugh