[Intel-gfx] [PATCH] drm/i915: rework dev->first_error locking

[Daniel Vetter]

- reduce the irq disabled section, even for a debugfs file this was
  way too long.
- always disable irqs when taking the lock.

v2: Thou shalt not mistake locking for reference counting, so:
- reference count the error_state to protect from concurent freeeing.
  This will be only really used in the next patch.

Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/i915/i915_debugfs.c |   13 ++++++++-----
 drivers/gpu/drm/i915/i915_drv.h     |    4 ++++
 drivers/gpu/drm/i915/i915_irq.c     |   17 ++++++++++-------
 3 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index a4dfab4..84ebbd6 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -769,12 +769,16 @@ static int i915_error_state(struct seq_file *m, void *unused)
 	int i, page, offset, elt;
 
 	spin_lock_irqsave(&dev_priv->error_lock, flags);
-	if (!dev_priv->first_error) {
+	error = dev_priv->first_error;
+	if (error)
+		kref_get(&error->ref);
+	spin_unlock_irqrestore(&dev_priv->error_lock, flags);
+
+	if (!error) {
 		seq_printf(m, "no error state collected\n");
-		goto out;
+		return 0;
 	}
 
-	error = dev_priv->first_error;
 
 	seq_printf(m, "Time: %ld s %ld us\n", error->time.tv_sec,
 		   error->time.tv_usec);
@@ -845,8 +849,7 @@ static int i915_error_state(struct seq_file *m, void *unused)
 	if (error->display)
 		intel_display_print_error_state(m, dev, error->display);
 
-out:
-	spin_unlock_irqrestore(&dev_priv->error_lock, flags);
+	kref_put(&error->ref, i915_error_state_free);
 
 	return 0;
 }
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 7be1474..005a062 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -37,6 +37,7 @@
 #include <linux/i2c.h>
 #include <drm/intel-gtt.h>
 #include <linux/backlight.h>
+#include <linux/kref.h>
 
 /* General customization:
  */
@@ -149,6 +150,7 @@ struct sdvo_device_mapping {
 struct intel_display_error_state;
 
 struct drm_i915_error_state {
+	struct kref ref;
 	u32 eir;
 	u32 pgtbl_er;
 	u32 pipestat[I915_MAX_PIPES];
@@ -387,6 +389,7 @@ typedef struct drm_i915_private {
 	unsigned int fsb_freq, mem_freq, is_ddr3;
 
 	spinlock_t error_lock;
+	/* Protected by dev->error_lock. */
 	struct drm_i915_error_state *first_error;
 	struct work_struct error_work;
 	struct completion error_completion;
@@ -1050,6 +1053,7 @@ extern int i915_vblank_pipe_get(struct drm_device *dev, void *data,
 				struct drm_file *file_priv);
 extern int i915_vblank_swap(struct drm_device *dev, void *data,
 			    struct drm_file *file_priv);
+void i915_error_state_free(struct kref *error_ref);
 
 void
 i915_enable_pipestat(drm_i915_private_t *dev_priv, int pipe, u32 mask);
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index a04d606..17f3ded 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -764,10 +764,11 @@ i915_error_object_free(struct drm_i915_error_object *obj)
 	kfree(obj);
 }
 
-static void
-i915_error_state_free(struct drm_device *dev,
-		      struct drm_i915_error_state *error)
+void
+i915_error_state_free(struct kref *error_ref)
 {
+	struct drm_i915_error_state *error = container_of(error_ref,
+							  typeof(*error), ref);
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(error->batchbuffer); i++)
@@ -941,6 +942,7 @@ static void i915_capture_error_state(struct drm_device *dev)
 	DRM_INFO("capturing error event; look for more information in /debug/dri/%d/i915_error_state\n",
 		 dev->primary->index);
 
+	kref_init(&error->ref);
 	error->eir = I915_READ(EIR);
 	error->pgtbl_er = I915_READ(PGTBL_ER);
 	for_each_pipe(pipe)
@@ -1017,21 +1019,22 @@ static void i915_capture_error_state(struct drm_device *dev)
 	spin_unlock_irqrestore(&dev_priv->error_lock, flags);
 
 	if (error)
-		i915_error_state_free(dev, error);
+		i915_error_state_free(&error->ref);
 }
 
 void i915_destroy_error_state(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct drm_i915_error_state *error;
+	unsigned long flags;
 
-	spin_lock(&dev_priv->error_lock);
+	spin_lock_irqsave(&dev_priv->error_lock, flags);
 	error = dev_priv->first_error;
 	dev_priv->first_error = NULL;
-	spin_unlock(&dev_priv->error_lock);
+	spin_unlock_irqrestore(&dev_priv->error_lock, flags);
 
 	if (error)
-		i915_error_state_free(dev, error);
+		kref_put(&error->ref, i915_error_state_free);
 }
 #else
 #define i915_capture_error_state(x)
-- 
1.7.6.3