X "Hangs" with RS690 + 2.6.26

[Jonathan McDowell]

Hi.

I've started to see "hangs" with X on an ATI RS690 with a 2.6.26 kernel.
The symptoms are that load average goes up, X stops accepting keypresses
or mouse clicks, but the cursor still moves around the screen in
response to the mouse being moved. I can't switch to a VT but can ssh in
remotely to see that things are still running. I don't seem to be able
to kill X but "shutdown -r now" cleanly reboots.

gdb fails to attach - complains about an internal error. strace shows
lots of ioctls against the DRM device all returning EBUSY.

2.6.25 appears to work fine. I originally had PAT enabled under 2.6.26
but have seen a patch fixing that go into git, so disabled it for my
2.6.26 kernel to see if that was the issue; no change AFAICT.

Enabling DRM debug (echo 1 > /sys/module/drm/parameters/debug) gives
lots of output from radeon_freelist_get, after the following ioctl is
received:

Jul 25 10:11:14 meepok kernel: [drm:drm_ioctl] pid=3302, cmd=0xc0406429, nr=0x29 , dev 0xe200, auth=1

and then a returning NULL message.

radeon driver is recent git - 1c5858484da4fb1c9bc3ac3b4d7a97863ab99730
but I've seen it with older revisions too.

It can take a couple of days for me to hit the problem, so a git bisect
could be a lengthy process. If anyone has any suggestions about faster
ways to track down the issue I'd like to hear them.

Machine is a dual core AMD64 with 4GB of RAM running Debian unstable,
card is:

01:05.0 VGA compatible controller [0300]: ATI Technologies Inc RS690 [Radeon X1200 Series] [1002:791e]

Kernel configs at:

http://the.earth.li/~noodles/radeon-2.6.26-hang/config-2.6.25
http://the.earth.li/~noodles/radeon-2.6.26-hang/config-2.6.26

Debug log from enabling drm debug:

http://the.earth.li/~noodles/radeon-2.6.26-hang/debug

Full dmesg (no obvious errors):

http://the.earth.li/~noodles/radeon-2.6.26-hang/meepok.dmesg

Xorg log file (no obvious errors):

http://the.earth.li/~noodles/radeon-2.6.26-hang/Xorg.0.log

J.

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