[ 57/79] drm/i915: Fix spurious -EIO/SIGBUS on wedged gpus

[Greg Kroah-Hartman]

3.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Vetter <daniel.vetter@xxxxxxxx>

commit 7abb690a0e095717420ba78dcab4309abbbec78a upstream.

Chris Wilson noticed that since

commit 1f83fee08d625f8d0130f9fe5ef7b17c2e022f3c [v3.9]
Author: Daniel Vetter <daniel.vetter@xxxxxxxx>
Date:   Thu Nov 15 17:17:22 2012 +0100

    drm/i915: clear up wedged transitions

X can again get -EIO when it does not expect it. And even worse score
a SIGBUS when accessing gtt mmaps. The established ABI is that we
_only_ return an -EIO from execbuf - all other ioctls should just
work. And since the reset code moves all bos out of gpu domains and
clears out all the last_seqno/ring tracking there really shouldn't be
any reason for non-execbuf code to ever touch the hw and see an -EIO.

After some extensive discussions we've noticed that these spurios -EIO
are caused by i915_gem_wait_for_error:

http://www.mail-archive.com/intel-gfx@xxxxxxxxxxxxxxxxxxxxx/msg20540.html

That is easy to fix by returning 0 instead of -EIO, since grabbing the
dev->struct_mutex does not yet mean that we actually want to touch the
hw. And so there is no reason at all to fail with -EIO.

But that's not the entire since, since often (at least it's easily
googleable) dmesg indicates that the reset fails and we declare the
gpu wedged. Then, quite a bit later X wakes up with the "Timed out
waiting for the gpu reset to complete" DRM_ERROR message in
wait_for_errror and brings down the desktop with an -EIO/SIGBUS.

So clearly we're missing a wakeup somewhere, since the gpu reset just
doesn't take 10 seconds to complete. And indeed we're do handle the
terminally wedged state wrong.

Fix this all up.

Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Damien Lespiau <damien.lespiau@xxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/i915/i915_gem.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -91,14 +91,11 @@ i915_gem_wait_for_error(struct i915_gpu_
 {
 	int ret;
 
-#define EXIT_COND (!i915_reset_in_progress(error))
+#define EXIT_COND (!i915_reset_in_progress(error) || \
+		   i915_terminally_wedged(error))
 	if (EXIT_COND)
 		return 0;
 
-	/* GPU is already declared terminally dead, give up. */
-	if (i915_terminally_wedged(error))
-		return -EIO;
-
 	/*
 	 * Only wait 10 seconds for the gpu reset to complete to avoid hanging
 	 * userspace. If it takes that long something really bad is going on and


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