Commit 0ca33adb authored by Haneen Mohammed's avatar Haneen Mohammed Committed by Daniel Vetter
Browse files

drm/vkms: Fix race condition around accessing frame number 



crtc_state is accessed by both vblank_handle() and the ordered
work_struct handle vkms_crc_work_handle() to retrieve and or update
the frame number for computed CRC.

Since work_struct can fail, add frame_end to account for missing frame
numbers.

Use (frame_[start/end]) for synchronization between hrtimer callback
and ordered work_struct handle.

This patch passes the following subtests from igt kms_pipe_crc_basic test:
bad-source, read-crc-pipe-A, read-crc-pipe-A-frame-sequence,
nonblocking-crc-pipe-A, nonblocking-crc-pipe-A-frame-sequence

Signed-off-by: default avatarHaneen Mohammed <hamohammed.sa@gmail.com>
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180903211743.GA2773@haneenDRM
parent 428e15cc

drivers/gpu/drm/vkms/vkms_crc.c

+34 −2
Original line number Diff line number Diff line
@@ -34,6 +34,15 @@ out: 
	return crc;

}



/**

 * vkms_crc_work_handle - ordered work_struct to compute CRC

 *

 * @work: work_struct

 *

 * Work handler for computing CRCs. work_struct scheduled in

 * an ordered workqueue that's periodically scheduled to run by

 * _vblank_handle() and flushed at vkms_atomic_crtc_destroy_state().

 */

void vkms_crc_work_handle(struct work_struct *work)

{

	struct vkms_crtc_state *crtc_state = container_of(work,
@@ -45,8 +54,18 @@ void vkms_crc_work_handle(struct work_struct *work) 
						output);

	struct vkms_crc_data *primary_crc = NULL;

	struct drm_plane *plane;



	u32 crc32 = 0;

	u64 frame_start, frame_end;

	unsigned long flags;



	spin_lock_irqsave(&out->state_lock, flags);

	frame_start = crtc_state->frame_start;

	frame_end = crtc_state->frame_end;

	spin_unlock_irqrestore(&out->state_lock, flags);



	/* _vblank_handle() hasn't updated frame_start yet */

	if (!frame_start || frame_start == frame_end)

		goto out;



	drm_for_each_plane(plane, &vdev->drm) {

		struct vkms_plane_state *vplane_state;
@@ -67,7 +86,20 @@ void vkms_crc_work_handle(struct work_struct *work) 
	if (primary_crc)

		crc32 = _vkms_get_crc(primary_crc);



	drm_crtc_add_crc_entry(crtc, true, crtc_state->n_frame, &crc32);

	frame_end = drm_crtc_accurate_vblank_count(crtc);



	/* queue_work can fail to schedule crc_work; add crc for

	 * missing frames

	 */

	while (frame_start <= frame_end)

		drm_crtc_add_crc_entry(crtc, true, frame_start++, &crc32);



out:

	/* to avoid using the same value for frame number again */

	spin_lock_irqsave(&out->state_lock, flags);

	crtc_state->frame_end = frame_end;

	crtc_state->frame_start = 0;

	spin_unlock_irqrestore(&out->state_lock, flags);

}



static int vkms_crc_parse_source(const char *src_name, bool *enabled)

drivers/gpu/drm/vkms/vkms_crtc.c

+14 −2
Original line number Diff line number Diff line
@@ -22,8 +22,19 @@ static void _vblank_handle(struct vkms_output *output) 
		DRM_ERROR("vkms failure on handling vblank");



	if (state && output->crc_enabled) {

		state->n_frame = drm_crtc_accurate_vblank_count(crtc);

		queue_work(output->crc_workq, &state->crc_work);

		u64 frame = drm_crtc_accurate_vblank_count(crtc);



		/* update frame_start only if a queued vkms_crc_work_handle()

		 * has read the data

		 */

		spin_lock(&output->state_lock);

		if (!state->frame_start)

			state->frame_start = frame;

		spin_unlock(&output->state_lock);



		ret = queue_work(output->crc_workq, &state->crc_work);

		if (!ret)

			DRM_WARN("failed to queue vkms_crc_work_handle");

	}



	spin_unlock(&output->lock);
@@ -211,6 +222,7 @@ int vkms_crtc_init(struct drm_device *dev, struct drm_crtc *crtc, 
	drm_crtc_helper_add(crtc, &vkms_crtc_helper_funcs);



	spin_lock_init(&vkms_out->lock);

	spin_lock_init(&vkms_out->state_lock);



	vkms_out->crc_workq = alloc_ordered_workqueue("vkms_crc_workq", 0);

drivers/gpu/drm/vkms/vkms_drv.h

+6 −2
Original line number Diff line number Diff line
@@ -39,12 +39,14 @@ struct vkms_plane_state { 
 * vkms_crtc_state - Driver specific CRTC state

 * @base: base CRTC state

 * @crc_work: work struct to compute and add CRC entries

 * @n_frame: frame number for computed CRC

 * @n_frame_start: start frame number for computed CRC

 * @n_frame_end: end frame number for computed CRC

 */

struct vkms_crtc_state {

	struct drm_crtc_state base;

	struct work_struct crc_work;

	unsigned int n_frame;

	u64 frame_start;

	u64 frame_end;

};



struct vkms_output {
@@ -59,6 +61,8 @@ struct vkms_output { 
	struct workqueue_struct *crc_workq;

	/* protects concurrent access to crc_data */

	spinlock_t lock;

	/* protects concurrent access to crtc_state */

	spinlock_t state_lock;

};



struct vkms_device {

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