Re: [Bug 87891] New: kernel BUG at mm/slab.c:2625!

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

On Tue, Nov 11, 2014 at 05:44:12PM -0800, Andrew Morton wrote:
> On Wed, 12 Nov 2014 10:22:45 +0900 Joonsoo Kim <iamjoonsoo.kim@lge.com> wrote:
> 
> > On Tue, Nov 11, 2014 at 05:02:43PM -0800, Andrew Morton wrote:
> > > On Wed, 12 Nov 2014 00:54:01 +0000 Luke Dashjr <luke@dashjr.org> wrote:
> > > 
> > > > On Wednesday, November 12, 2014 12:49:13 AM Andrew Morton wrote:
> > > > > But anyway - Luke, please attach your .config to
> > > > > https://bugzilla.kernel.org/show_bug.cgi?id=87891?
> > > > 
> > > > Done: https://bugzilla.kernel.org/attachment.cgi?id=157381
> > > > 
> > > 
> > > OK, thanks.  No CONFIG_HIGHMEM of course.  I'm stumped.
> > 
> > Hello, Andrew.
> > 
> > I think that the cause is GFP_HIGHMEM.
> > GFP_HIGHMEM is always defined regardless CONFIG_HIGHMEM.
> > Please look at the do_huge_pmd_anonymous_page().
> > It calls alloc_hugepage_vma() and then alloc_pages_vma() is called
> > with alloc_hugepage_gfpmask(). This gfpmask includes GFP_TRANSHUGE
> > and then GFP_HIGHUSER_MOVABLE.
> 
> OK.
> 
> So where's the bug?  I'm inclined to say that it's in ttm.  It's taking

I agree that.

> a gfp_mask which means "this is the allocation attempt which we are
> attempting to satisfy" and uses that for its own allocation.
> 
> But ttm has no business using that gfp_mask for its own allocation
> attempt.  If anything it should use something like, err,
> 
> 	GFP_KERNEL & ~__GFP_IO & ~__GFP_FS | __GFP_HIGH
> 
> although as I mentioned earlier, it would be better to avoid allocation
> altogether.

Yes, avoiding would be the best.

If not possible, introducing new common helper for changing shrinker
control's gfp to valid allocation gfp is better than just open code.

Thanks.

> 
> Poor ttm guys - this is a bit of a trap we set for them.
> 
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