Hi Dave, On Saturday 21 August 2010 10:50:21 Dave Airlie wrote: > 2010/8/21 Oldřich Jedlička <[email protected]>: > > On Friday 20 August 2010 11:05:40 Christopher James Halse Rogers wrote: > >> On Fri, 2010-08-20 at 07:55 +0200, Oldřich Jedlička wrote: > >> > On Friday 20 August 2010 02:04:35 Christopher James Halse Rogers wrote: > >> > > On Thu, 2010-08-19 at 21:23 +0200, Oldřich Jedlička wrote: > >> > > > On Thursday 19 August 2010 10:57:21 Christopher James Halse Rogers > > > > wrote: > >> > > > > When a client calls ScheduleSwap we set up a kernel callback > >> > > > > when the relevent vblank event occurs. However, it's possible > >> > > > > for the client to go away between calling ScheduleSwap and the > >> > > > > vblank event, resulting in the buffers being destroyed before > >> > > > > they're passed to radeon_dri2_frame_event_handler. > >> > > > > >> > > > I was also thinking about the solution and did some xorg-server > >> > > > investigation. Personally I don't like comparing pointer values > >> > > > (ClientPtr), because it could be the same - sequence > >> > > > malloc/free/malloc could return the same pointer value. > >> > > > >> > > Yeah, there is a chance that a stray DRI2_SwapBuffersComplete event > >> > > could be written to an uninterested client. It certainly won't try > >> > > to write to an invalid client, though, so it shouldn't crash X. > >> > > And it is reasonably unlikely that a client will go away and a new > >> > > client will both fill the same slot *and* get the same memory > >> > > address - there's a lot of memory allocation going on in the > >> > > surrounding code. > >> > > >> > Question is if the client can handle this :-) > >> > > >> > > > Here are two other possible solutions: > >> > > > > >> > > > 1. Add a "uniqueId" (increasing number with each client) to > >> > > > ClientRec. Then you can compare something really unique. On the > >> > > > other hand this needs change in xorg-server. > >> > > > > >> > > > 2. Use AddCallback(&ClientStateCallback, > >> > > > our_client_state_changed_method, 0) during driver initialization > >> > > > to detect that any client went away and invalidate its events > >> > > > (add field "valid" in event). That would be even better than > >> > > > solution 1 - no change of xorg-server is needed. Each client > >> > > > could have private data too - double-linked list of pending > >> > > > events - registered with dixRegisterPrivateKey(). The event would > >> > > > be removed from the list only when it is valid (otherwise the > >> > > > prev/next list pointers would be invalid too). Invalid events > >> > > > would be ignored in the handler, they would be only freed. > >> > > > >> > > I thought about that, too. It seemed a bit excessive for the driver > >> > > to maintain a list of clients as they come and go just for the > >> > > purpose of not sending an event when a client quits. > >> > > >> > There is no need to have a list of clients. Each client would have the > >> > list of events kept in the client's devPrivate area (registered with > >> > dixRegisterPrivateKey, found by dixLookupPrivate) - ony the event list > >> > head is necessary: > >> > > >> > 1. The event would have "prev" and "next" pointers for the purposes of > >> > the list and a new "valid" boolean field. > >> > > >> > 2. Register Client State callback by the call to AddCallback and call > >> > dixRegisterPrivateKey in the driver initialization routine. Add > >> > RemoveCallback in the driver shut-down routine. > >> > > >> > 3. Whenever new client connects, the list head would be set to 0 (done > >> > in the Client State callback). This step is probably unnecessary if > >> > the area is set to 0 via calloc (I'm just not sure). > >> > > >> > 4. Whenever the new event is created, dixLookupPrivate would get the > >> > client's list head and the new event would be added to the list head. > >> > > >> > 5. Whenever the client dies (recognized in the Client State callback), > >> > the list would be walked-through and events invalidated (valid=false). > >> > > >> > 6. For valid events (valid==true) on event callback the event would be > >> > removed from the list (just modify the event's prev's "next" and > >> > event's next's "prev" pointers, eventually modifying the client's > >> > list head). > >> > > >> > 7. For invalid events (valid==false) the list would stay unmodified > >> > (because of the list head modification on freed client's memory), only > >> > the event would be freed. > >> > > >> > This looks to me like a few lines of code for each point, nothing big. > >> > >> Ah, right. That's the reverse of what I was thinking; it's more > >> reasonable. > >> > >> It still seems a bit heavyweight to me for this corner case. > > > > Yeah, looks so. I think it is now the ATI driver developpers turn to say > > what they want - if your patch is good or needs enhancing. > > > >> > > The pointer comparison is quick, cheap, and ensures we won't crash > >> > > X. > >> > > >> > Yes, that should work most of the time :-) But this might add some > >> > hard-to- reproduce problem with client getting unwanted message. > >> > > >> > > > Personally I like solution 2, because it fully uses xorg-server > >> > > > facilities. But I don't know if this isn't too much or if there > >> > > > exists a simpler solution. > >> > > > >> > > I think that there should actually be solution 3: the DRI2 extension > >> > > handles this for drivers as a part of the swapbuffers/waitmsc common > >> > > code. > >> > > >> > Yes, definitely. > >> > > >> > But it looks like the driver is currently scheduling the event (and > >> > holding wrong data - ClientPtr) and handling it, only notifying DRI2 > >> > on xserver about the result. So that would mean creating some common > >> > part that handles event creation/handling/invalidation. The driver > >> > would call xserver when the event arrives and xserver would call > >> > driver back if it still applies. Or something simillar... > >> > >> Well, the need to reference count buffers could easily be be removed by > >> having DRI2ScheduleSwap take a reference to the buffers and > >> DRI2SwapComplete decrement that, in the same way that it handles > >> pending_swaps and such already. > >> > >> Similarly, if we need to handle the Client gone fun it could be handled > >> there. > > > > That's right. Maybe somebody from xorg-devel list would be interrested. > > It would probably be better to move this discussion to xorg-devel, or > at least involve Kristian,. > > I'll try and review this thread next week if I can, I suck at dealing > with swapbuffers stuff
Alban Browaeys has implemented a patch that uses client's private area to keep the list of pending events and invalidating them when the client has gone. See bug 29065 (https://bugs.freedesktop.org/show_bug.cgi?id=29065) for the patch (for the xf86-video-ati package). Oldřich. > > Dave. _______________________________________________ xorg-driver-ati mailing list [email protected] http://lists.x.org/mailman/listinfo/xorg-driver-ati
