Application that renders using libva/vdpau/opengl hangs after a few minutes of operation (always reproducible within 1-15 minutes usually).
 
I see a hang in xcb_wait_for_reply() for request #31161:
 
Possibly relevant part of xtrace:
000:>:4d8a:32: Reply to SwapBuffers: swap_hi=0 swap_lo=31161
000:>:4d8b:32: Reply to GetInputFocus: revert-to=Parent(0x02) focus=0x02e000e0
000:<:24d8c: 20: DRI2-Request(155,7): GetBuffersWithFormat drawable=0x04400006 attachments={attachment=BackLeft(0x00000001) format=0x00000020};
000:>:24d8c: Event DRI2-BufferSwapComplete(102) drawable=0x00000002 ust_hi=71303174 ust_lo=0 msc_hi=1858207713 msc_lo=0 sbc_hi=109393 sbc_lo=31161
 
And:
000:<:31161:  4: Request(43): GetInputFocus  
000:>:31161: Event DRI2-InvalidateBuffers(103) drawable=0x04400006
 
Backtrace of thread waiting in xcb_wait_for_reply():
 
Thread 8 (Thread 0x7fca1f778700 (LWP 3580)):
#0  0x00007fca55a3e12d in poll () at ../sysdeps/unix/syscall-template.S:81
#1  0x00007fca5316b262 in poll (__timeout=-1, __nfds=1, __fds=0x7fca1f776a20) at
    /usr/include/x86_64-linux-gnu/bits/poll2.h:46
#2  _xcb_conn_wait (c=c@entry=0x2885500, cond=cond@entry=0x7fca1f776b40,
        vector=vector@entry=0x0, count=count@entry=0x0) at xcb_conn.c:459
#3  0x00007fca5316cadf in wait_for_reply (c=c@entry=0x2885500, request=31161,
        e=e@entry=0x0) at xcb_in.c:491
#4  0x00007fca5316cbf2 in xcb_wait_for_reply (c=0x2885500, request=31161, e=0x0)
at xcb_in.c:521
#5  0x00007fca419b8004 in vl_dri2_get_flush_reply (scrn=0x2653600) at
../../../../../src/gallium/auxiliary/vl/vl_winsys_dri.c:110
#6  0x00007fca419b8101 in vl_dri2_destroy_drawable (scrn=0x2653600) at
../../../../../src/gallium/auxiliary/vl/vl_winsys_dri.c:153
#7  0x00007fca419b8185 in vl_dri2_set_drawable (scrn=0x2653600,
        drawable=71303307) at
../../../../../src/gallium/auxiliary/vl/vl_winsys_dri.c:176
#8  0x00007fca419b82c8 in vl_dri2_screen_texture_from_drawable
(vscreen=0x2653600, drawable=0x440008b) at
../../../../../src/gallium/auxiliary/vl/vl_winsys_dri.c:193
#9  0x00007fca419b61ab in vlVdpPresentationQueueDisplay
(presentation_queue=<optimized out>, surface=5, clip_width=1280,
 clip_height=720, earliest_presentation_time=0)
        at ../../../../../../src/gallium/state_trackers/vdpau/presentation.c:234
#10 0x00007fca423ca6a3 in flip_surface_unlocked
        (driver_data=driver_data@entry=0x2650c90,
         obj_output=obj_output@entry=0x291a2b0) at vdpau_video_x11.c:583
#11 0x00007fca423cb2e1 in queue_surface_unlocked (obj_surface=<optimized out>,
        obj_output=0x291a2b0, driver_data=0x2650c90) at vdpau_video_x11.c:610
#12 put_surface_unlocked (flags=32, target_rect=0x7fca1f776f90,
        source_rect=0x7fca1f776f80, obj_output=0x291a2b0, obj_surface=0x2919bf0,
        driver_data=0x2650c90) at vdpau_video_x11.c:689
#13 put_surface (driver_data=driver_data@entry=0x2650c90,
        surface=surface@entry=50331655, drawable=drawable@entry=71303307,
        drawable_width=<optimized out>, drawable_height=720,
            source_rect=source_rect@entry=0x7fca1f776f80,
            target_rect=target_rect@entry=0x7fca1f776f90, flags=flags@entry=32)
at vdpau_video_x11.c:755
#14 0x00007fca423cb59c in vdpau_PutSurface (ctx=<optimized out>,
        surface=50331655, draw=0x440008b, srcx=<optimized out>, srcy=<optimized
        out>, srcw=<optimized out>, srch=720, destx=0, desty=0,
            destw=1280, desth=720, cliprects=0x0, number_cliprects=0, flags=32)
at vdpau_video_x11.c:808
#15 0x000000000040eed2 in on_client_draw (glsink=<optimized out>, buf=<optimized
        out>, data=0x626d40 <video>) at video.c:619


Full backtrace at: http://pastebin.com/rQCJm64C

Using:

libX11 1.6.2
libxcb 1.10 or 1.11
mesa 11.0 (11.0~git1508070730.42d283~gd~t from oibaf/graphics-drivers ppa)
xserver-xorg-video-radeon 1:7.5.99+git1508070731.3791fc~gd~t (same ppa)