Re: [PATCH v2] drm/i915/guc: Clean up locks in GuC

[Nick Hoath <nicholas.hoath@intel.com>]

On 25/11/2015 19:29, Dai, Yu wrote:
> From: Alex Dai <yu.dai@intel.com>
>
> When GuC Work Queue is full, driver will wait GuC for avaliable
                                                         available
> space by delaying 1ms. The wait needs to be out of spinlockirq /
> unlock. Otherwise, lockup happens because jiffies won't be updated
> dur to irq is disabled. The unnecessary locks has been cleared.
   due        being                              have
> dev->struct_mutex is used instead where needed.
>
> Issue is found in igt/gem_close_race.
>
> v2: Clean up wq_lock too
> v1: Clean up host2guc lock as well
>
> Signed-off-by: Alex Dai <yu.dai@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_debugfs.c        | 12 +++++------
>   drivers/gpu/drm/i915/i915_guc_submission.c | 32 +++++++-----------------------
>   drivers/gpu/drm/i915/intel_guc.h           |  4 ----
>   3 files changed, 13 insertions(+), 35 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index a728ff1..d6b7817 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -2473,15 +2473,15 @@ static int i915_guc_info(struct seq_file *m, void *data)
>   	if (!HAS_GUC_SCHED(dev_priv->dev))
>   		return 0;
>
> +	if (mutex_lock_interruptible(&dev->struct_mutex))
> +		return 0;
> +
>   	/* Take a local copy of the GuC data, so we can dump it at leisure */
> -	spin_lock(&dev_priv->guc.host2guc_lock);
>   	guc = dev_priv->guc;
> -	if (guc.execbuf_client) {
> -		spin_lock(&guc.execbuf_client->wq_lock);
> +	if (guc.execbuf_client)
>   		client = *guc.execbuf_client;
> -		spin_unlock(&guc.execbuf_client->wq_lock);
> -	}
> -	spin_unlock(&dev_priv->guc.host2guc_lock);
> +
> +	mutex_unlock(&dev->struct_mutex);
>
>   	seq_printf(m, "GuC total action count: %llu\n", guc.action_count);
>   	seq_printf(m, "GuC action failure count: %u\n", guc.action_fail);
> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
> index ed9f100..97996e5 100644
> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
> @@ -86,7 +86,6 @@ static int host2guc_action(struct intel_guc *guc, u32 *data, u32 len)
>   		return -EINVAL;
>
>   	intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL);
> -	spin_lock(&dev_priv->guc.host2guc_lock);
>
>   	dev_priv->guc.action_count += 1;
>   	dev_priv->guc.action_cmd = data[0];
> @@ -119,7 +118,6 @@ static int host2guc_action(struct intel_guc *guc, u32 *data, u32 len)
>   	}
>   	dev_priv->guc.action_status = status;
>
> -	spin_unlock(&dev_priv->guc.host2guc_lock);
>   	intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);
>
>   	return ret;
> @@ -249,6 +247,7 @@ static int guc_ring_doorbell(struct i915_guc_client *gc)
>   	}
>
>   	kunmap_atomic(base);
> +
Unnecessary whitespace churn
>   	return ret;
>   }
>
> @@ -292,16 +291,12 @@ static uint32_t select_doorbell_cacheline(struct intel_guc *guc)
>   	const uint32_t cacheline_size = cache_line_size();
>   	uint32_t offset;
>
> -	spin_lock(&guc->host2guc_lock);
> -
>   	/* Doorbell uses a single cache line within a page */
>   	offset = offset_in_page(guc->db_cacheline);
>
>   	/* Moving to next cache line to reduce contention */
>   	guc->db_cacheline += cacheline_size;
>
> -	spin_unlock(&guc->host2guc_lock);
> -
>   	DRM_DEBUG_DRIVER("selected doorbell cacheline 0x%x, next 0x%x, linesize %u\n",
>   			offset, guc->db_cacheline, cacheline_size);
>
> @@ -322,13 +317,11 @@ static uint16_t assign_doorbell(struct intel_guc *guc, uint32_t priority)
>   	const uint16_t end = start + half;
>   	uint16_t id;
>
> -	spin_lock(&guc->host2guc_lock);
>   	id = find_next_zero_bit(guc->doorbell_bitmap, end, start);
>   	if (id == end)
>   		id = GUC_INVALID_DOORBELL_ID;
>   	else
>   		bitmap_set(guc->doorbell_bitmap, id, 1);
> -	spin_unlock(&guc->host2guc_lock);
>
>   	DRM_DEBUG_DRIVER("assigned %s priority doorbell id 0x%x\n",
>   			hi_pri ? "high" : "normal", id);
> @@ -338,9 +331,7 @@ static uint16_t assign_doorbell(struct intel_guc *guc, uint32_t priority)
>
>   static void release_doorbell(struct intel_guc *guc, uint16_t id)
>   {
> -	spin_lock(&guc->host2guc_lock);
>   	bitmap_clear(guc->doorbell_bitmap, id, 1);
> -	spin_unlock(&guc->host2guc_lock);
>   }
>
>   /*
> @@ -487,16 +478,13 @@ static int guc_get_workqueue_space(struct i915_guc_client *gc, u32 *offset)
>   	struct guc_process_desc *desc;
>   	void *base;
>   	u32 size = sizeof(struct guc_wq_item);
> -	int ret = 0, timeout_counter = 200;
> +	int ret = -ETIMEDOUT, timeout_counter = 200;
>
>   	base = kmap_atomic(i915_gem_object_get_page(gc->client_obj, 0));
>   	desc = base + gc->proc_desc_offset;
>
>   	while (timeout_counter-- > 0) {
> -		ret = wait_for_atomic(CIRC_SPACE(gc->wq_tail, desc->head,
> -				gc->wq_size) >= size, 1);
> -
> -		if (!ret) {
> +		if (CIRC_SPACE(gc->wq_tail, desc->head, gc->wq_size) >= size) {
>   			*offset = gc->wq_tail;
>
>   			/* advance the tail for next workqueue item */
> @@ -505,7 +493,11 @@ static int guc_get_workqueue_space(struct i915_guc_client *gc, u32 *offset)
>
>   			/* this will break the loop */
>   			timeout_counter = 0;
> +			ret = 0;
>   		}
> +
> +		if (timeout_counter)
> +			usleep_range(1000, 2000);
>   	};
>
>   	kunmap_atomic(base);
> @@ -597,15 +589,12 @@ int i915_guc_submit(struct i915_guc_client *client,
>   {
>   	struct intel_guc *guc = client->guc;
>   	enum intel_ring_id ring_id = rq->ring->id;
> -	unsigned long flags;
>   	int q_ret, b_ret;
>
>   	/* Need this because of the deferred pin ctx and ring */
>   	/* Shall we move this right after ring is pinned? */
>   	lr_context_update(rq);
>
> -	spin_lock_irqsave(&client->wq_lock, flags);
> -
>   	q_ret = guc_add_workqueue_item(client, rq);
>   	if (q_ret == 0)
>   		b_ret = guc_ring_doorbell(client);
> @@ -620,12 +609,8 @@ int i915_guc_submit(struct i915_guc_client *client,
>   	} else {
>   		client->retcode = 0;
>   	}
> -	spin_unlock_irqrestore(&client->wq_lock, flags);
> -
> -	spin_lock(&guc->host2guc_lock);
>   	guc->submissions[ring_id] += 1;
>   	guc->last_seqno[ring_id] = rq->seqno;
> -	spin_unlock(&guc->host2guc_lock);
>
>   	return q_ret;
>   }
> @@ -768,7 +753,6 @@ static struct i915_guc_client *guc_client_alloc(struct drm_device *dev,
>   	client->client_obj = obj;
>   	client->wq_offset = GUC_DB_SIZE;
>   	client->wq_size = GUC_WQ_SIZE;
> -	spin_lock_init(&client->wq_lock);
>
>   	client->doorbell_offset = select_doorbell_cacheline(guc);
>
> @@ -871,8 +855,6 @@ int i915_guc_submission_init(struct drm_device *dev)
>   	if (!guc->ctx_pool_obj)
>   		return -ENOMEM;
>
> -	spin_lock_init(&dev_priv->guc.host2guc_lock);
> -
>   	ida_init(&guc->ctx_ids);
>
>   	guc_create_log(guc);
> diff --git a/drivers/gpu/drm/i915/intel_guc.h b/drivers/gpu/drm/i915/intel_guc.h
> index 5ba5866..8229522 100644
> --- a/drivers/gpu/drm/i915/intel_guc.h
> +++ b/drivers/gpu/drm/i915/intel_guc.h
> @@ -42,8 +42,6 @@ struct i915_guc_client {
>
>   	uint32_t wq_offset;
>   	uint32_t wq_size;
> -
> -	spinlock_t wq_lock;		/* Protects all data below	*/
>   	uint32_t wq_tail;
>
>   	/* GuC submission statistics & status */
> @@ -95,8 +93,6 @@ struct intel_guc {
>
>   	struct i915_guc_client *execbuf_client;
>
> -	spinlock_t host2guc_lock;	/* Protects all data below	*/
> -
>   	DECLARE_BITMAP(doorbell_bitmap, GUC_MAX_DOORBELLS);
>   	uint32_t db_cacheline;		/* Cyclic counter mod pagesize	*/
>
>

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