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

[Davidlohr Bueso]

On Mon, 2014-04-28 at 15:05 -0700, Hugh Dickins wrote:
> On Mon, 28 Apr 2014, Linus Torvalds wrote:
> > On Mon, Apr 28, 2014 at 2:20 PM, Linus Torvalds
> > <torvalds@xxxxxxxxxxxxxxxxxxxx> 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.

I think that returning some stale/bogus vma is causing those segfaults
in udev. It shouldn't occur in a normal scenario. What puzzles me is
that it's not always reproducible. This makes me wonder what else is
going on...

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