i915 modeset memory corruption issues? (Fwd: Oops in ext3_block_to_path.isra.40+0x26/0x11b)

[Jerome Glisse]

On Sat, 2012-03-17 at 14:14 -0700, Linus Torvalds wrote:
> On Sat, Mar 17, 2012 at 1:23 PM, Dave Airlie <airlied at gmail.com> wrote:
> >
> > I did however get a flashback in google to this:
> >
> > http://lists.fedoraproject.org/pipermail/scm-commits/2010-July/456636.html
> >
> > Linus don't think we ever did work out why that worked, I wonder if we
> > lost something after that.
> 
> Hmm. Maybe we should stop making the default gfp_mask be
> GFP_HIGHMEM_MOVABLE (see inode_init_always() in fs/inode.c), and
> instead add the _MOVABLE flag only for mappings that use
> "generic_file_mmap()".
> 
> It does sound a bit scary to just make default mappings use MOVABLE
> pages, when we know that can be incorrect for some cases.
> 
> But that would require that filesystems like ext4 etc that don't just
> use the generic_file_mmap() function would have add do that MOVABLE
> thing on their own. And the *normal* case is certainly that pages are
> movable and putting them in themovable zone should be ok. It's just
> *not* ok if you also map them into some hardware GTT thing or just
> otherwise keep track of the pages directly, like DRI does.
> 
> The other possibility is to just make this a shm thing, since it's
> generally that layer that has the case of "pages allocated with the
> mapping gfp masks". Hugh Dickins clearly tried to make sure that the
> DRM initialization of the gfp mask was honored, but maybe there is
> some case where it is missed. Hugh added a mapping_set_gfp_mask() to
> i915_gem_alloc_object(), but maybe we have i915 shmem mappings that
> get set up through some other path.
> 
> What about the ttm swap storage thing, for example? That also does
> shmem_file_setup(), without limiting the pages. But I don't think i915
> uses ttm, right?

It's not an issue for ttm, as we never us page allocated through shmem
for the hw. We use shmem to swapout buffer object (ttm_tt_swapout func
in ttm_tt.c).

Cheers,
Jerome