Created attachment 29769 [details]
lspci -vv output for the video card

When eg. moving cursor over kde menu, or moving a window, X hangs, and starts using 100% cpu. Sometimes it even hangs before kde has finished loading. It pretty much hangs in under a minute if i do anything at all.
The cursor still moves, but nothing else works.

More specific info, as obtained from "gdb --pid `pidof X`", follows.
The hanged X sometimes shuts down after i detach from it, the odds seem to rise the more i have used stepi in gdb.

Backtrace: (gdb's parameter string expansions removed, as they contained garbage. They are visible in the attached gdb-full.log, though)
#0  0x00007fc4c3af5127 in ioctl () from /lib/libc.so.6
#1  0x00007fc4c2d8bb26 in drmIoctl (fd=9, request=1074291845, arg=0x7fffec89f5c0) at xf86drm.c:188
#2  0x00007fc4c2d8bd3f in drmCommandWrite (fd=9, drmCommandIndex=<value optimized out>, data=0x7fffec89f5c0, size=18446744073709551615) at xf86drm.c:2402
#3  0x00007fc4c2930011 in nouveau_bo_wait (bo=0x2397790, cpu_write=0, no_wait=0, no_block=0) at nouveau_bo.c:399
#4  0x00007fc4c29301d5 in nouveau_bo_map_range (bo=0x2397790, delta=0, size=<value optimized out>, flags=0) at nouveau_bo.c:442
#5  0x00007fc4c2b43ce5 in NVAccelDownloadM2MF (pspix=0x2614d70, x=<value optimized out>, y=0, w=156, h=102,
    dst=0x2614db0, dst_pitch=624) at nouveau_exa.c:125
#6  0x00007fc4c2b44d1e in nouveau_exa_download_from_screen (pspix=0x2614d70, x=0, y=0, w=156, h=102,
    dst=0x2614db0, dst_pitch=624) at nouveau_exa.c:480
#7  0x00007fc4c10d271a in exaCopyDirty (migrate=0x7fffec89f950, pValidDst=0x2517ee8, pValidSrc=<value optimized out>, transfer=0x7fc4c2b44ca7 <nouveau_exa_download_from_screen>,
    fallback_src=0x7fc4b9000b00 <Address 0x7fc4b9000b00 out of bounds>,
--
#8  0x00007fc4c10d2a69 in exaDoMoveOutPixmap (migrate=0x7fffec89f950) at exa_migration.c:256
#9  0x00007fc4c10d30b5 in exaDoMigration (pixmaps=0x7fffec89f950, npixmaps=1, can_accel=0) at exa_migration.c:677
#10 0x00007fc4c10cf329 in exaGetImage (pDrawable=0x2614d70, x=0, y=0, w=156, h=102, format=2, planeMask=4294967295, d=0x2624660) at exa_accel.c:1331
#11 0x00000000004cc141 in miSpriteGetImage (pDrawable=0x2614d70, sx=0, sy=0, w=156, h=102, format=2, planemask=4294967295, pdstLine=0x2624660) at misprite.c:281
#12 0x0000000000446116 in ProcGetImage (client=0x2528750) at dispatch.c:2067
#13 0x0000000000447c4a in Dispatch () at dispatch.c:454
#14 0x000000000043069d in main (argc=9, argv=0x7fffec89fc78, envp=<value optimized out>) at main.c:438

I've gotten the above(ish) backtrace multiple times, the last few functions are always the same:
ioctl()
drmIoctl()
drmCommandWrite()
nouveau_bo_wait() (was "?? ()" before i compiled everything with -ggdb, but probably same)
nouveau_bo_map_range()

Right next in the stack trace after these, i have seen NVAccelDownloadM2MF and NVAccelUploadM2MF thus far. (again before recompile with -ggdb, it was always "?? ()", so i might've missed some callers, but probably mostly the same functions)

If i step the code one instruction at a time with 'stepi', the execution loops these:

ioctl () from /lib/libc.so.6
0x7fc4c3af5127 <ioctl+7>:       cmp    $0xfffffffffffff001,%rax

utils.c
0x4df396 <SmartScheduleTimer>:  mov    0x2b47a3(%rip),%rax        # 0x793b40 <_DYNAMIC+3496>
0x4df39d <SmartScheduleTimer+7>:        mov    0x2b4b54(%rip),%rdx        # 0x793ef8 <_DYNAMIC+4448>
0x4df3a4 <SmartScheduleTimer+14>:       mov    (%rdx),%rdx
0x4df3a7 <SmartScheduleTimer+17>:       add    %rdx,(%rax)
0x4df3aa <SmartScheduleTimer+20>:       retq

<signal handler called>
0x7fc4c5b8ea10 <__restore_rt>:  mov    $0xf,%rax
0x7fc4c5b8ea17 <__restore_rt+7>:        syscall

So the line in ioctl() never seems to get executed. The assembly lines looped have so far been the same every time i have looked at X with gdb after a hang.

I am using 64bit gentoo, the git revisions of the installed packages are:
xf86-video-nouveau df94ebdbcd89c1678ac243217e7f5b20cbbe857c
nouveau-drm 3d6747a2b1576782fe74975a353b356cfc936505
libdrm ac71f0849928f4b2fbb69c01304ac6f9df8916a1

Like i said, it's very easy to trigger the hang, so on the positive side, i'm able to test patches quickly (as soon as i figure out how to tell emerge to use them :)