Re: kernel BUG at mm/rmap.c:480 in 2.6.10-rc3-bk7

[Hugh Dickins]

On Wed, 15 Dec 2004, Greg KH wrote:
> On Wed, Dec 15, 2004 at 05:23:14PM +0000, Hugh Dickins wrote:
> > 
> > I think it very likely that your page_remove_rmap BUGs are caused by
> > the first idea that occurred to me, months back, which intervening
> > reports didn't seem to fit with: PageReserved(page) when the page is
> > mapped into userspace, but !PageReserved(page) when it gets unmapped.
> > 
> > Which would suggest some kind of refcounting bug in drivers/char/drm/,
> > such that the reserved pages get unreserved and freed before their
> > last unmap.  I've started looking for that, but drivers/char/drm/ is
> > unfamiliar territory to me, so I'd be glad for someone to beat me to it.
...
> > I'll report back whether they confirm or refute the hypothesis.
> 
> Here's the files.  gish.map has the map file and I've put the dmesg
> output inline below.

Thanks a lot.  They seem to refute the PageReserved -> !PageReserved
theory.  It sure looks like a problem in this area (gish.maps shows
this vma maps /dev/dri/card0), but not quite what I was expecting.

> If there's anything else I can do to help out, please let me know.

Thanks: I'm sure there will be later, but right now I need to
look further around that source before proposing anything more.

> Bad rmap in gish: page c1279380 flags 20000014 count 3 mapcount 0 addr b6913000 vm_flags 800fb
....
> Bad rmap in gish: page c127d360 flags 20000014 count 2 mapcount 0 addr b6b12000 vm_flags 800fb

And in gish.maps:
> b6b13000-b6b14000 r--s d8246000 00:0a 10806      /dev/dri/card0

Hugh

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