Re: [backport v3.12 PATCH 1/3] mm: pass VM_BUG_ON() reason to dump_page()

[Jiri Slaby <jslaby@suse.cz>]

On 05/10/2016, 05:43 AM, Gavin Guo wrote:
> From: Dave Hansen <dave.hansen@linux.intel.com>
> 
> commit e4f674229ce63dac60be0c4ddfb5ef8d1225d30d upstream
> 
> I recently added a patch to let folks pass a "reason" string dump_page()
> which gets dumped out along with the page's data.  This essentially
> saves the bug-reader a trip in to the source to figure out why we
> BUG_ON()'d.
> 
> The new VM_BUG_ON_PAGE() passes in NULL for "reason".  It seems like we
> might as well pass the BUG_ON() condition if we have it.  This will
> bloat kernels a bit with ~160 new strings, but this is all under a
> debugging option anyway.
> 
> 	page:ffffea0008560280 count:1 mapcount:0 mapping:(null) index:0x0
> 	page flags: 0xbfffc0000000001(locked)
> 	page dumped because: VM_BUG_ON_PAGE(PageLocked(page))
> 	------------[ cut here ]------------
> 	kernel BUG at /home/davehans/linux.git/mm/filemap.c:464!
> 	invalid opcode: 0000 [#1] SMP
> 	CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.14.0+ #251
> 	Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> 	...
> 
> [akpm@linux-foundation.org: include stringify.h]
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Acked-by: Davidlohr Bueso <davidlohr@hp.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> [fixes the conflict and includes the VM_BUG_ON_PAGE]
> Signed-off-by: Gavin Guo <gavin.guo@canonical.com>
> ---
>  include/linux/mmdebug.h | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h
> index 580bd587d916..fa387ca7218c 100644
> --- a/include/linux/mmdebug.h
> +++ b/include/linux/mmdebug.h
> @@ -1,10 +1,19 @@
>  #ifndef LINUX_MM_DEBUG_H
>  #define LINUX_MM_DEBUG_H 1
>  
> +#include <linux/stringify.h>
>  #ifdef CONFIG_DEBUG_VM
>  #define VM_BUG_ON(cond) BUG_ON(cond)
> +#define VM_BUG_ON_PAGE(cond, page)					\
> +	do {								\
> +		if (unlikely(cond)) {					\
> +			dump_page(page, "VM_BUG_ON_PAGE(" __stringify(cond)")");\

But dump_page in 3.12 accepts only one parameter.

And this is not the commit which actually added VM_BUG_ON_PAGE. The one
which did, included also dump_page prototype in this header.

Instead, I would just change VM_BUG_ON_PAGE to VM_BUG_ON in the second
patch.

thanks,
-- 
js
suse labs