drm/i915: Move debug only per-request pid tracking from request to ctx

Since contexts are not currently shared between userspace processes, we
have an exact correspondence between context creator and guilty batch
submitter. Therefore we can save some per-batch work by inspecting the
context->pid upon error instead. Note that we take the context's
creator's pid rather than the file's pid in order to better track fd
passed over sockets.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471254551-25805-29-git-send-email-chris@chris-wilson.co.uk
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index bd58878..d9f2924 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -782,6 +782,7 @@
 
 		struct drm_i915_error_request {
 			long jiffies;
+			pid_t pid;
 			u32 seqno;
 			u32 head;
 			u32 tail;
@@ -880,6 +881,7 @@
 	struct drm_i915_private *i915;
 	struct drm_i915_file_private *file_priv;
 	struct i915_hw_ppgtt *ppgtt;
+	struct pid *pid;
 
 	struct i915_ctx_hang_stats hang_stats;