On Mon, Sep 21, 2015 at 06:17:34PM -0700, Guenter Roeck wrote:

On 09/21/2015 08:34 AM, Kirill A. Shutemov wrote:

quoted

Guenter Roeck wrote:

quoted

On 09/18/2015 07:53 AM, Jesper Nilsson wrote:

quoted

On Fri, Sep 18, 2015 at 05:25:07PM +0300, Kirill A. Shutemov wrote:

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On Thu, Sep 17, 2015 at 09:29:27AM -0700, Guenter Roeck wrote:

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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);

page:c04a5340 count:1 mapcount:1 mapping:c1f34080 index:0xc1f34060
flags: 0x80(slab)
page dumped because: page
page:c1f17a04 count:0 mapcount:1 mapping:00d13600 index:0xc0
flags: 0x0()
page dumped because: compound_head(page)

Does that help ?

Kinda. It's false positive PageTail() due low bit set in
page->rcu_head.next.

It happens (at least) due broken alignment of 'rcu' field within
task_struct -- offsetof(struct task_struct, rcu): 773.

That's looks veery broken. I would guess compiler does something horribly
wrong. I hope it's not an ABI issue. :-/

Mikael? Jesper?

-- 
 Kirill A. Shutemov