Subject: Re: crisv32 runtime failure in -next due to 'page-flags: define behavior SL*B-related flags on compound pages'

From: "Kirill A. Shutemov" <[email-masked]>
Date: Mon, 21 Sep 2015 18:34:35 +0300 (EEST)

Guenter Roeck wrote:
> On 09/18/2015 07:53 AM, Jesper Nilsson wrote:
> > On Fri, Sep 18, 2015 at 05:25:07PM +0300, Kirill A. Shutemov wrote:
> >> On Thu, Sep 17, 2015 at 09:29:27AM -0700, Guenter Roeck wrote:
> >>> Hi,
> >>>
> >>> my crisv32 qemu test fails with next-20150917 as follows.
> >>>
> >>> NET: Registered protocol family 16
> >>> kernel BUG at mm/slab.c:1648!
> >>> Linux 4.3.0-rc1-next-20150917 #1 Wed Sep 16 23:56:59 PDT 2015
> >>> Oops: 0000
> >>>
> >>> [ register dump follows ]
> >>>
> >>> See http://server.roeck-us.net:8010/builders/qemu-crisv32-next/builds/83/steps/qemubuildcommand/logs/stdio
> >>> for a complete log.
> >>
> >> Is there a chance to get proper backtrace?
> >
> > Yes, it should be possible with CONFIG_KALLSYMS=y in the kconfig.
> >
> 
> Good to know. I added it to my configuration.
> 
> Here it is:
> 
> kernel BUG at mm/slab.c:1648!

I still don't understand what's going on :(
Could you try with this instrumentation:

diff --git a/mm/slab.c b/mm/slab.c
index ce9c6531e6f7..10035d1a06d3 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1645,7 +1645,11 @@ static void kmem_freepages(struct kmem_cache *cachep, struct page *page)
                sub_zone_page_state(page_zone(page),
                                NR_SLAB_UNRECLAIMABLE, nr_freed);
 
-       BUG_ON(!PageSlab(page));
+       if (!PageSlab(page)) {
+               dump_page(page, "page");
+               dump_page(compound_head(page), "compound_head(page)");
+               BUG();
+       }
        __ClearPageSlabPfmemalloc(page);
        __ClearPageSlab(page);
        page_mapcount_reset(page);
-- 
 Kirill A. Shutemov