[Intel-gfx] [PATCH] drm/atomic: Make drm_atomic_legacy_backoff reset crtc->acquire_ctx

[Daniel Vetter]

On Thu, Jun 23, 2016 at 01:45:06PM +0200, Maarten Lankhorst wrote:
> Atomic updates may acquire more state than initially locked through
> drm_modeset_lock_crtc, running with heavy stress can cause a
> WARN_ON(crtc->acquire_ctx) in drm_modeset_lock_crtc:
> 
> [  601.491296] ------------[ cut here ]------------
> [  601.491366] WARNING: CPU: 0 PID: 2411 at
> drivers/gpu/drm/drm_modeset_lock.c:191 drm_modeset_lock_crtc+0xeb/0xf0 [drm]
> [  601.491369] Modules linked in: drm i915 drm_kms_helper
> [  601.491414] CPU: 0 PID: 2411 Comm: kms_cursor_lega Tainted: G     U 4.7.0-rc4-patser+ #4798
> [  601.491417] Hardware name: Intel Corporation Skylake Client
> [  601.491420]  0000000000000000 ffff88044d153c98 ffffffff812ead28 0000000000000000
> [  601.491425]  0000000000000000 ffff88044d153cd8 ffffffff810868e6 000000bf58058030
> [  601.491431]  ffff880088b415e8 ffff880458058030 ffff88008a271548 ffff88008a271568
> [  601.491436] Call Trace:
> [  601.491443]  [<ffffffff812ead28>] dump_stack+0x4d/0x65
> [  601.491447]  [<ffffffff810868e6>] __warn+0xc6/0xe0
> [  601.491452]  [<ffffffff81086968>] warn_slowpath_null+0x18/0x20
> [  601.491472]  [<ffffffffc00d4ffb>] drm_modeset_lock_crtc+0xeb/0xf0 [drm]
> [  601.491491]  [<ffffffffc00c5526>] drm_mode_cursor_common+0x66/0x180 [drm]
> [  601.491509]  [<ffffffffc00c91cc>] drm_mode_cursor_ioctl+0x3c/0x40 [drm]
> [  601.491524]  [<ffffffffc00bc94d>] drm_ioctl+0x14d/0x530 [drm]
> [  601.491540]  [<ffffffffc00c9190>] ? drm_mode_setcrtc+0x520/0x520 [drm]
> [  601.491545]  [<ffffffff81176aeb>] ? handle_mm_fault+0x106b/0x1430
> [  601.491550]  [<ffffffff81108441>] ? stop_one_cpu+0x61/0x70
> [  601.491556]  [<ffffffff811bb71d>] do_vfs_ioctl+0x8d/0x570
> [  601.491560]  [<ffffffff81290d7e>] ? security_file_ioctl+0x3e/0x60
> [  601.491565]  [<ffffffff811bbc74>] SyS_ioctl+0x74/0x80
> [  601.491571]  [<ffffffff810e321c>] ? posix_get_monotonic_raw+0xc/0x10
> [  601.491576]  [<ffffffff8175b11b>] entry_SYSCALL_64_fastpath+0x13/0x8f
> [  601.491581] ---[ end trace 56f3d3d85f000d00 ]---
> 
> For good measure, test mode_config.acquire_ctx too, although this should
> never happen.
> 
> Testcase: kms_cursor_legacy
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>

It's kinda a bug in the skl wm code which unecessarily looks at other
plane state.

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Given that this is fairly hard to hit, but will blow in really strange
ways in practice I think also justified for backporting.

Cc: stable at vger.kernel.org

Dave, can you pls pick up for -fixes directly?

Thanks, Daniel

> ---
>  drivers/gpu/drm/drm_atomic.c | 27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index d99ab2f6663f..3cee084e9d28 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -1299,14 +1299,39 @@ EXPORT_SYMBOL(drm_atomic_add_affected_planes);
>   */
>  void drm_atomic_legacy_backoff(struct drm_atomic_state *state)
>  {
> +	struct drm_device *dev = state->dev;
> +	unsigned crtc_mask = 0;
> +	struct drm_crtc *crtc;
>  	int ret;
> +	bool global = false;
> +
> +	drm_for_each_crtc(crtc, dev) {
> +		if (crtc->acquire_ctx != state->acquire_ctx)
> +			continue;
> +
> +		crtc_mask |= drm_crtc_mask(crtc);
> +		crtc->acquire_ctx = NULL;
> +	}
> +
> +	if (WARN_ON(dev->mode_config.acquire_ctx == state->acquire_ctx)) {
> +		global = true;
> +
> +		dev->mode_config.acquire_ctx = NULL;
> +	}
>  
>  retry:
>  	drm_modeset_backoff(state->acquire_ctx);
>  
> -	ret = drm_modeset_lock_all_ctx(state->dev, state->acquire_ctx);
> +	ret = drm_modeset_lock_all_ctx(dev, state->acquire_ctx);
>  	if (ret)
>  		goto retry;
> +
> +	drm_for_each_crtc(crtc, dev)
> +		if (drm_crtc_mask(crtc) & crtc_mask)
> +			crtc->acquire_ctx = state->acquire_ctx;
> +
> +	if (global)
> +		dev->mode_config.acquire_ctx = state->acquire_ctx;
>  }
>  EXPORT_SYMBOL(drm_atomic_legacy_backoff);
>  
> -- 
> 2.5.5
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch