Re: [PATCH] x86/mm: print domain IDs instead of pointers

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 05/06/15 11:27, Jan Beulich wrote:
> Printing pointers to struct domain isn't really useful for initial
> problem analysis. In get_page() also drop the page only after issuing
> the log message, so that at the time of printing the state can be
> considered reasonably consistent.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

There are a few areas of code which seem overzealous with printing Xen
pointers.

> ---
> It also slightly concerns me that page_get_owner_and_reference() can
> (at least theoretically) return NULL even after having taken a page
> reference (when ->v.inuse._domain is clear), in which case that
> reference would never get dropped again. One case where this might be a
> problem is sh_set_allocation(), which - other than all other uses of
> page_set_owner(, NULL) - doesn't zap the refcount.

Looks as if page_get_owner_and_reference() should drop the ref itself if
->v.inuse._domain is clear.

Alternatively, the implication is that page_get_owner_and_reference() is
called on a page with a real owner, which might justify an ASSERT/BUG.

A different area which concerns me is __acquire_grant_for_copy() which
ignores the return value.  The caller of __acquire_grant_for_copy() cant
actually be certain that a ref was taken on the page, based on a return
value of GNTST_okay.

~Andrew