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

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Date:	Mon, 28 Apr 2014 15:05:43 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Linux MM <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Davidlohr Bueso <davidlohr@...com>,
	Rik van Riel <riel@...hat.com>,
	Michel Lespinasse <walken@...gle.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [BUG] kernel BUG at mm/vmacache.c:85!

On Mon, 28 Apr 2014, Linus Torvalds wrote:
> On Mon, Apr 28, 2014 at 2:20 PM, Linus Torvalds
> <torvalds@...ux-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
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