Re: [PATCH] drm/xlnx: fix kmemleak by sending vblank_event in atomic_disable

[Daniel Vetter]

On Tue, Feb 02, 2021 at 02:41:21PM +0800, quanyang.wang@xxxxxxxxxxxxx wrote:
> From: Quanyang Wang <quanyang.wang@xxxxxxxxxxxxx>
> 
> When running xrandr to change resolution of DP, the kmemleak as below
> can be observed:
> 
> unreferenced object 0xffff00080a351000 (size 256):
>   comm "Xorg", pid 248, jiffies 4294899614 (age 19.960s)
>   hex dump (first 32 bytes):
>     98 a0 bc 01 08 00 ff ff 01 00 00 00 00 00 00 00  ................
>     ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace:
>     [<00000000e0bd0f69>] kmemleak_alloc+0x30/0x40
>     [<00000000cde2f318>] kmem_cache_alloc+0x3d4/0x588
>     [<0000000088ea9bd7>] drm_atomic_helper_setup_commit+0x84/0x5f8
>     [<000000002290a264>] drm_atomic_helper_commit+0x58/0x388
>     [<00000000f6ea78c3>] drm_atomic_commit+0x4c/0x60
>     [<00000000c8e0725e>] drm_atomic_connector_commit_dpms+0xe8/0x110
>     [<0000000020ade187>] drm_mode_obj_set_property_ioctl+0x1b0/0x450
>     [<00000000918206d6>] drm_connector_property_set_ioctl+0x3c/0x68
>     [<000000008d51e7a5>] drm_ioctl_kernel+0xc4/0x118
>     [<000000002a819b75>] drm_ioctl+0x214/0x448
>     [<000000008ca4e588>] __arm64_sys_ioctl+0xa8/0xf0
>     [<0000000034e15a35>] el0_svc_common.constprop.0+0x74/0x190
>     [<000000001b93d916>] do_el0_svc+0x24/0x90
>     [<00000000ce9230e0>] el0_svc+0x14/0x20
>     [<00000000e3607d82>] el0_sync_handler+0xb0/0xb8
>     [<000000003e79c15f>] el0_sync+0x174/0x180
> 
> This is because there is a scenario that a drm_crtc_commit commit is
> allocated but not freed. The drm subsystem require/release references
> to a CRTC commit by calling drm_crtc_commit_get/put, and when
> drm_crtc_commit_put find that commit.ref.refcount is zero, it will
> call __drm_crtc_commit_free to free this CRTC commit. Among these
> drm_crtc_commit_get/put pairs, there is a drm_crtc_commit_get in
> drm_atomic_helper_setup_commit as below:
> 
> ...
> new_crtc_state->event->base.completion = &commit->flip_done;
> new_crtc_state->event->base.completion_release = release_crtc_commit;
> drm_crtc_commit_get(commit);
> ...
> 
> This reference to the CRTC commit should be released at the function
> release_crtc_commit by calling e->completion_release(e->completion) in
> drm_send_event_locked. So we need to call drm_send_event_locked at
> two places: handling vblank event in the irq handler and the crtc disable
> helper. But in zynqmp_disp_crtc_atomic_disable, it only marks the flip
> is done and not call drm_crtc_commit_put. This result that the refcount
> of this commit is always non-zero and this commit will never be freed.
> 
> Since the function drm_crtc_send_vblank_event has operations both sending
> a flip_done signal and releasing reference to the CRTC commit, let's use
> it instead.
> 
> Signed-off-by: Quanyang Wang <quanyang.wang@xxxxxxxxxxxxx>

Yeah that's the way to do it, not the hack. Thanks for your patch, I'll
push it to drm-misc-fixes with Cc: stable@xxxxxxxxxxxxxxx

Cheers, Daniel


> ---
>  drivers/gpu/drm/xlnx/zynqmp_disp.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xlnx/zynqmp_disp.c b/drivers/gpu/drm/xlnx/zynqmp_disp.c
> index 68cc4ffff969..ee7657a48e6a 100644
> --- a/drivers/gpu/drm/xlnx/zynqmp_disp.c
> +++ b/drivers/gpu/drm/xlnx/zynqmp_disp.c
> @@ -1396,19 +1396,11 @@ static void zynqmp_disp_enable(struct zynqmp_disp *disp)
>   */
>  static void zynqmp_disp_disable(struct zynqmp_disp *disp)
>  {
> -	struct drm_crtc *crtc = &disp->crtc;
> -
>  	zynqmp_disp_audio_disable(&disp->audio);
>  
>  	zynqmp_disp_avbuf_disable_audio(&disp->avbuf);
>  	zynqmp_disp_avbuf_disable_channels(&disp->avbuf);
>  	zynqmp_disp_avbuf_disable(&disp->avbuf);
> -
> -	/* Mark the flip is done as crtc is disabled anyway */
> -	if (crtc->state->event) {
> -		complete_all(crtc->state->event->base.completion);
> -		crtc->state->event = NULL;
> -	}
>  }
>  
>  static inline struct zynqmp_disp *crtc_to_disp(struct drm_crtc *crtc)
> @@ -1499,6 +1491,13 @@ zynqmp_disp_crtc_atomic_disable(struct drm_crtc *crtc,
>  
>  	drm_crtc_vblank_off(&disp->crtc);
>  
> +	spin_lock_irq(&crtc->dev->event_lock);
> +	if (crtc->state->event) {
> +		drm_crtc_send_vblank_event(crtc, crtc->state->event);
> +		crtc->state->event = NULL;
> +	}
> +	spin_unlock_irq(&crtc->dev->event_lock);
> +
>  	clk_disable_unprepare(disp->pclk);
>  	pm_runtime_put_sync(disp->dev);
>  }
> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch