From f1925f3309d13d431f70e7b6b72ba59cae90fdff Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Fri, 13 Dec 2019 16:03:47 +0000
Subject: [PATCH] drm/i915: Use EAGAIN for trylock failures
Git-commit: f1925f3309d13d431f70e7b6b72ba59cae90fdff
Patch-mainline: v5.6-rc1
References: bsc#1174737

While not good behaviour, it is, however, established behaviour that we
can punt EAGAIN to userspace if we need to retry the ioctl. When trying
to acquire a mutex, prefer to use EAGAIN to propagate losing the race
so that if it does end up back in userspace, we try again.

Fixes: c81471f5e95c ("drm/i915: Copy across scheduler behaviour flags across submit fences")
Closes: https://gitlab.freedesktop.org/drm/intel/issues/800
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191213160347.1789004-1-chris@chris-wilson.co.uk
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/i915/i915_request.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -800,7 +800,7 @@ i915_request_await_start(struct i915_req
 	if (!tl) /* already started or maybe even completed */
 		return 0;
 
-	fence = ERR_PTR(-EBUSY);
+	fence = ERR_PTR(-EAGAIN);
 	if (mutex_trylock(&tl->mutex)) {
 		fence = NULL;
 		if (!i915_request_started(signal) &&