On Fri, 1 Feb 2008, Andrea Arcangeli wrote: > On Thu, Jan 31, 2008 at 02:21:58PM -0800, Christoph Lameter wrote: > > Is this okay for KVM too? > > ->release isn't implemented at all in KVM, only the list_del generates > complications.
Why would the list_del generate problems? > I think current code could be already safe through the mm_count pin, > becasue KVM relies on the fact anybody pinning through mm_count like > KVM does, is forbidden to call unregister and it's forced to wait the > auto-disarming when mm_users hits zero, but I feel like something's > still wrong if I think that I'm not using call_rcu to free the > notifier (OTOH we agreed the list had to be frozen and w/o readers > (modulo _release) before _release is called, so if this initial > assumption is ok it seems I may be safe w/o call_rcu?). You could pin via mm_users? Then it would be entirely safe and no need for rcu tricks? OTOH if there are mm_count users like in KVM: Could we guarantee that they do not perform any operations with the mmu notifier list? Then we would be safe as well. > too soon ;) so let's concentrate on the rest first. I can say > hlist_del_init doesn't seem to provide any benefit given nobody could > possibly decide to call register or unregister after _release run. It is useful if a device driver has a list of data segments that contain struct mmu_notifiers. The device driver can inspect the mmu_notifier and reliably conclude that the beast is inactive. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
