[PATCH] drm/msm/mdp5: Fix global state lock backoff

From: Rob Clark <robdclark@gmail.com>
To: dri-devel@lists.freedesktop.org
Cc: freedreno@lists.freedesktop.org, linux-arm-msm@vger.kernel.org,
	Rob Clark <robdclark@chromium.org>,
	Rob Clark <robdclark@gmail.com>,
	Abhinav Kumar <quic_abhinavk@quicinc.com>,
	Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
	Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
	Daniel Vetter <daniel@ffwll.ch>,
	Jessica Zhang <quic_jesszhan@quicinc.com>,
	linux-kernel@vger.kernel.org (open list)
Subject: [PATCH] drm/msm/mdp5: Fix global state lock backoff
Date: Thu,  7 Jul 2022 09:20:37 -0700	[thread overview]
Message-ID: <20220707162040.1594855-1-robdclark@gmail.com> (raw)

From: Rob Clark <robdclark@chromium.org>

We need to grab the lock after the early return for !hwpipe case.
Otherwise, we could have hit contention yet still returned 0.

Fixes an issue that the new CONFIG_DRM_DEBUG_MODESET_LOCK stuff flagged
in CI:

   WARNING: CPU: 0 PID: 282 at drivers/gpu/drm/drm_modeset_lock.c:296 drm_modeset_lock+0xf8/0x154
   Modules linked in:
   CPU: 0 PID: 282 Comm: kms_cursor_lega Tainted: G        W         5.19.0-rc2-15930-g875cc8bc536a #1
   Hardware name: Qualcomm Technologies, Inc. DB820c (DT)
   pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
   pc : drm_modeset_lock+0xf8/0x154
   lr : drm_atomic_get_private_obj_state+0x84/0x170
   sp : ffff80000cfab6a0
   x29: ffff80000cfab6a0 x28: 0000000000000000 x27: ffff000083bc4d00
   x26: 0000000000000038 x25: 0000000000000000 x24: ffff80000957ca58
   x23: 0000000000000000 x22: ffff000081ace080 x21: 0000000000000001
   x20: ffff000081acec18 x19: ffff80000cfabb80 x18: 0000000000000038
   x17: 0000000000000000 x16: 0000000000000000 x15: fffffffffffea0d0
   x14: 0000000000000000 x13: 284e4f5f4e524157 x12: 5f534b434f4c5f47
   x11: ffff80000a386aa8 x10: 0000000000000029 x9 : ffff80000cfab610
   x8 : 0000000000000029 x7 : 0000000000000014 x6 : 0000000000000000
   x5 : 0000000000000001 x4 : ffff8000081ad904 x3 : 0000000000000029
   x2 : ffff0000801db4c0 x1 : ffff80000cfabb80 x0 : ffff000081aceb58
   Call trace:
    drm_modeset_lock+0xf8/0x154
    drm_atomic_get_private_obj_state+0x84/0x170
    mdp5_get_global_state+0x54/0x6c
    mdp5_pipe_release+0x2c/0xd4
    mdp5_plane_atomic_check+0x2ec/0x414
    drm_atomic_helper_check_planes+0xd8/0x210
    drm_atomic_helper_check+0x54/0xb0
    ...
   ---[ end trace 0000000000000000 ]---
   drm_modeset_lock attempting to lock a contended lock without backoff:
      drm_modeset_lock+0x148/0x154
      mdp5_get_global_state+0x30/0x6c
      mdp5_pipe_release+0x2c/0xd4
      mdp5_plane_atomic_check+0x290/0x414
      drm_atomic_helper_check_planes+0xd8/0x210
      drm_atomic_helper_check+0x54/0xb0
      drm_atomic_check_only+0x4b0/0x8f4
      drm_atomic_commit+0x68/0xe0

Fixes: d59be579fa93 ("drm/msm/mdp5: Return error code in mdp5_pipe_release when deadlock is detected")
Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.c
index a4f5cb90f3e8..e4b8a789835a 100644
--- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.c
+++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.c
@@ -123,12 +123,13 @@ int mdp5_pipe_release(struct drm_atomic_state *s, struct mdp5_hw_pipe *hwpipe)
 {
 	struct msm_drm_private *priv = s->dev->dev_private;
 	struct mdp5_kms *mdp5_kms = to_mdp5_kms(to_mdp_kms(priv->kms));
-	struct mdp5_global_state *state = mdp5_get_global_state(s);
+	struct mdp5_global_state *state;
 	struct mdp5_hw_pipe_state *new_state;
 
 	if (!hwpipe)
 		return 0;
 
+	state = mdp5_get_global_state(s);
 	if (IS_ERR(state))
 		return PTR_ERR(state);
 
-- 
2.36.1

