Re: Xen 4.6.0-rc1 build with lock_profile=y crash_debug=y, frame_pointer=y and domain.c:241: error: negative width in bit-field ‘<anonymous>’

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Aug 25, 2015 at 05:48:58PM +0100, Andrew Cooper wrote:
> On 25/08/15 17:43, Konrad Rzeszutek Wilk wrote:
> > I am troubleshooting an locking issue and figured I would enable extra options.
> >
> > But now I am hitting this build issue:
> >
> > domain.c:241: error: negative width in bit-field ‘<anonymous>’
> >
> > Which is:
> >
> >  229 struct domain *alloc_domain_struct(void)
> >  230 {
> >  231     struct domain *d;
> > ...
> >  241     BUILD_BUG_ON(sizeof(*d) > PAGE_SIZE);
> >
> > Thoughts?
> 
> That is to catch the case where sizeof struct domain exceeds PAGE_SIZE.
> 
> The logic behind this was to prevent needing order 1 allocations for
> domains or vcpus, and therefore allocation failures in heavily memory
> fragmented situations.
> 
> It means we will probably need to find some other areas of struct domain
> to shrink, or move out into a separate xmalloc().
> 
> For straight debugging, it is acceptable to drop the BUILD_BUG_ON().  If
> we can't drop the size of struct domain, we might want to move to using
> vmalloc() instead.

It is big. pahole says:

   /* size: 4352, cachelines: 68, members: 74 */ 
    /* sum members: 4238, holes: 9, sum holes: 34 */ 
    /* padding: 80 */ 
    /* paddings: 1, sum paddings: 4 */

Would this patch be OK then:
diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 045f6ff..cc9ce0b 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -238,7 +238,9 @@ struct domain *alloc_domain_struct(void)
     if ( unlikely(!bits) )
          bits = _domain_struct_bits();
 
+#ifndef LOCK_PROFILE
     BUILD_BUG_ON(sizeof(*d) > PAGE_SIZE);
+#endif
     d = alloc_xenheap_pages(0, MEMF_bits(bits));
     if ( d != NULL )
         clear_page(d);

(not compile tested nor runtime tested)

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