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

[Abhinav Kumar]

On 7/7/2022 9:20 AM, Rob Clark wrote:
> From: Rob Clark <robdclark at 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 at chromium.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk at quicinc.com>
> ---
>   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);
>