For cris it is completely valid to do that. It has been an issue before. If you for some reason really require dword alignment there should be an align in the struct.

CC:ing the compiler guy for further comments.

Best regard
/Mikael

22 sep 2015 kl. 14:03 skrev Kirill A. Shutemov [off-list ref]:

quoted

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

quoted

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

quoted

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:

quoted

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);

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