Gregory Haskins wrote: >>>> On Tue, May 8, 2007 at 4:13 AM, in message <[EMAIL PROTECTED]>, >>>> > Avi Kivity <[EMAIL PROTECTED]> wrote: > >> Gregory Haskins wrote: >> >>> I am perhaps being a bit overzealous here. What I found in practice is >>> that >>> >> the LVTT can screw things up on shutdown, so I was being pretty conservative >> on the synchronization here. >> >>> >>> >> That may point out to a different sync problem. All pending timers >> ought to have been canceled before we reach here. Please check to make >> sure this isn't papering over another problem. >> >> > > You are definitely right there. I had added this logic in the early stage of > debugging. It turned out that I was missing an apic_dropref, which > effectively meant the hrtimer_cancel() was never being issued. That was the > root-cause of my "LVTT expiration after guest shutdown" bug. I left the sync > code in as a conservative measure, but I will clean this up. > >
Okay. An alternative to removing it is replacing it with a BUG_ON() so make sure the constraint is checked. >>> >>> >> I approach it from the other direction: to me, a locked assignment says >> that something is fundamentally wrong. Usually anything under a lock is >> a read- modify- write operation, otherwise the writes just stomp on each >> other. >> >> > > Interesting. That makes sense. So if I replace the assignment cases with > wmb, do I need to sprinkle rmbs anywhere or is that take care of naturally by > the places where we take the lock for a compound operation? > I was going to say yes, but I'm not so sure now. In any case I'm still uneasy about the lack of rmw in there. See Documentation/memory-barriers.txt for an interesting, if difficult, discussion of the subject. >>> >>> >> No, you are correct wrt the vcpu migrating to another cpu. >> >> What about vs. exit to userspace where we may sleep? >> > > My logic being correct is predicated on the assumption that you and I made a > week or two ago: That the user-space will not sleep for anything but HLT. > If userspace *can* sleep on other things besides HLT, I agree that there is a > race here. If it is limited to HLT, we will be taken care of by the virtue > of the fact that irq.pending be set before the handle_halt() logic is > checked. I admit that I was coding against an assumption that I do not yet > know for a fact to be true. I will update the comments to note this > assumption so its clearer, and we can address it in the future if its ever > revealed to be false. > Yeah, I keep forgetting this. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
