On 26/2/07 23:31, "Hollis Blanchard" <[EMAIL PROTECTED]> wrote:
> > Hi Yamahata-san, thanks very much for your patch! > > I'm confused about one thing though: why do we need to take a lock to > read d->grant_table->nr_grant_frames? It's a simple integer, so no lock > is required or useful. I haven't got the ppc code immediately to hand but the x86 code will dynamically grow the grant table based on requests made via the add_to_physmap hypercall, hence it needs to take the lock. I see ia64 takes it also even though it only reads from nr_grant_frames (it won;t dynamically expand via the add_to_physmap hypercall). That's possibly overkill although there is some concern over reading nr_grant_frames versus looking up a grant-table page that appears within the range [0, nr_grant_frames-1] which taking the lock trivially sidesteps. If ia64 didn't take the lock it might be possible to see an increased value of nr_grant_frames that the expand function hadn't yet fully installed the new grant-table pages for yet. -- Keir _______________________________________________ Xen-ppc-devel mailing list Xen-ppc-devel@lists.xensource.com http://lists.xensource.com/xen-ppc-devel
