Re: [PATCH v2] drm/msm/dpu: Avoid ABBA deadlock between IRQ modules

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On 11/06/2021 20:00, Bjorn Andersson wrote:

Handling of the interrupt callback lists is done in dpu_core_irq.c,
under the "cb_lock" spinlock. When these operations results in the need
for enableing or disabling the IRQ in the hardware the code jumps to
dpu_hw_interrupts.c, which protects its operations with "irq_lock"
spinlock.

When an interrupt fires, dpu_hw_intr_dispatch_irq() inspects the
hardware state while holding the "irq_lock" spinlock and jumps to
dpu_core_irq_callback_handler() to invoke the registered handlers, which
traverses the callback list under the "cb_lock" spinlock.

As such, in the event that these happens concurrently we'll end up with
a deadlock.

Prior to '1c1e7763a6d4 ("drm/msm/dpu: simplify IRQ enabling/disabling")'
the enable/disable of the hardware interrupt was done outside the
"cb_lock" region, optimitically by using an atomic enable-counter for
each interrupt and an warning print if someone changed the list between
the atomic_read and the time the operation concluded.

Rather than re-introducing the large array of atomics, this change
embraces the fact that dpu_core_irq and dpu_hw_interrupts are deeply
entangled and make them share the single "irq_lock".

Following this step it's suggested that we squash the two parts into a
single irq handling thing.

Fixes: 1c1e7763a6d4 ("drm/msm/dpu: simplify IRQ enabling/disabling")
Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>


Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>


---

Changes since v1:
- Make dpu_core_irq use dpu_hw_interrupts' irq_lock instead of adding another
   mutex.

  drivers/gpu/drm/msm/disp/dpu1/dpu_core_irq.c  | 27 ++++-----
  .../gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c | 60 +++++++++++--------
  .../gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.h | 20 ++++++-
  drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h       |  2 -
  4 files changed, 63 insertions(+), 46 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_core_irq.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_core_irq.c
index 4f110c428b60..18557b9713b6 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_core_irq.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_core_irq.c
@@ -22,7 +22,6 @@ static void dpu_core_irq_callback_handler(void *arg, int irq_idx)
  	struct dpu_kms *dpu_kms = arg;
  	struct dpu_irq *irq_obj = &dpu_kms->irq_obj;
  	struct dpu_irq_callback *cb;
-	unsigned long irq_flags;
pr_debug("irq_idx=%d\n", irq_idx); @@ -34,11 +33,9 @@ static void dpu_core_irq_callback_handler(void *arg, int irq_idx) 
  	/*
  	 * Perform registered function callback
  	 */
-	spin_lock_irqsave(&dpu_kms->irq_obj.cb_lock, irq_flags);
  	list_for_each_entry(cb, &irq_obj->irq_cb_tbl[irq_idx], list)
  		if (cb->func)
  			cb->func(cb->arg, irq_idx);
-	spin_unlock_irqrestore(&dpu_kms->irq_obj.cb_lock, irq_flags);
  }
u32 dpu_core_irq_read(struct dpu_kms *dpu_kms, int irq_idx, bool clear) 
@@ -82,22 +79,21 @@ int dpu_core_irq_register_callback(struct dpu_kms *dpu_kms, int irq_idx,
DPU_DEBUG("[%pS] irq_idx=%d\n", __builtin_return_address(0), irq_idx); - spin_lock_irqsave(&dpu_kms->irq_obj.cb_lock, irq_flags); 
+	irq_flags = dpu_kms->hw_intr->ops.lock(dpu_kms->hw_intr);
  	trace_dpu_core_irq_register_callback(irq_idx, register_irq_cb);
  	list_del_init(&register_irq_cb->list);
  	list_add_tail(&register_irq_cb->list,
  			&dpu_kms->irq_obj.irq_cb_tbl[irq_idx]);
  	if (list_is_first(&register_irq_cb->list,
  			&dpu_kms->irq_obj.irq_cb_tbl[irq_idx])) {
-		int ret = dpu_kms->hw_intr->ops.enable_irq(
+		int ret = dpu_kms->hw_intr->ops.enable_irq_locked(
  				dpu_kms->hw_intr,
  				irq_idx);
  		if (ret)
  			DPU_ERROR("Fail to enable IRQ for irq_idx:%d\n",
  					irq_idx);
  	}
-
-	spin_unlock_irqrestore(&dpu_kms->irq_obj.cb_lock, irq_flags);
+	dpu_kms->hw_intr->ops.unlock(dpu_kms->hw_intr, irq_flags);
return 0; 
  }
@@ -127,12 +123,12 @@ int dpu_core_irq_unregister_callback(struct dpu_kms *dpu_kms, int irq_idx,
DPU_DEBUG("[%pS] irq_idx=%d\n", __builtin_return_address(0), irq_idx); - spin_lock_irqsave(&dpu_kms->irq_obj.cb_lock, irq_flags); 
+	irq_flags = dpu_kms->hw_intr->ops.lock(dpu_kms->hw_intr);
  	trace_dpu_core_irq_unregister_callback(irq_idx, register_irq_cb);
  	list_del_init(&register_irq_cb->list);
  	/* empty callback list but interrupt is still enabled */
  	if (list_empty(&dpu_kms->irq_obj.irq_cb_tbl[irq_idx])) {
-		int ret = dpu_kms->hw_intr->ops.disable_irq(
+		int ret = dpu_kms->hw_intr->ops.disable_irq_locked(
  				dpu_kms->hw_intr,
  				irq_idx);
  		if (ret)
@@ -140,7 +136,7 @@ int dpu_core_irq_unregister_callback(struct dpu_kms *dpu_kms, int irq_idx,
  					irq_idx);
  		DPU_DEBUG("irq_idx=%d ret=%d\n", irq_idx, ret);
  	}
-	spin_unlock_irqrestore(&dpu_kms->irq_obj.cb_lock, irq_flags);
+	dpu_kms->hw_intr->ops.unlock(dpu_kms->hw_intr, irq_flags);
return 0; 
  }
@@ -164,7 +160,8 @@ static void dpu_disable_all_irqs(struct dpu_kms *dpu_kms)
  #ifdef CONFIG_DEBUG_FS
  static int dpu_debugfs_core_irq_show(struct seq_file *s, void *v)
  {
-	struct dpu_irq *irq_obj = s->private;
+	struct dpu_kms *dpu_kms = s->private;
+	struct dpu_irq *irq_obj = &dpu_kms->irq_obj;
  	struct dpu_irq_callback *cb;
  	unsigned long irq_flags;
  	int i, irq_count, cb_count;
@@ -173,12 +170,12 @@ static int dpu_debugfs_core_irq_show(struct seq_file *s, void *v)
  		return 0;
for (i = 0; i < irq_obj->total_irqs; i++) { 
-		spin_lock_irqsave(&irq_obj->cb_lock, irq_flags);
+		irq_flags = dpu_kms->hw_intr->ops.lock(dpu_kms->hw_intr);
  		cb_count = 0;
  		irq_count = atomic_read(&irq_obj->irq_counts[i]);
  		list_for_each_entry(cb, &irq_obj->irq_cb_tbl[i], list)
  			cb_count++;
-		spin_unlock_irqrestore(&irq_obj->cb_lock, irq_flags);
+		dpu_kms->hw_intr->ops.unlock(dpu_kms->hw_intr, irq_flags);
if (irq_count || cb_count) 
  			seq_printf(s, "idx:%d irq:%d cb:%d\n",
@@ -193,7 +190,7 @@ DEFINE_SHOW_ATTRIBUTE(dpu_debugfs_core_irq);
  void dpu_debugfs_core_irq_init(struct dpu_kms *dpu_kms,
  		struct dentry *parent)
  {
-	debugfs_create_file("core_irq", 0600, parent, &dpu_kms->irq_obj,
+	debugfs_create_file("core_irq", 0600, parent, dpu_kms,
  		&dpu_debugfs_core_irq_fops);
  }
  #endif
@@ -207,8 +204,6 @@ void dpu_core_irq_preinstall(struct dpu_kms *dpu_kms)
  	dpu_disable_all_irqs(dpu_kms);
  	pm_runtime_put_sync(&dpu_kms->pdev->dev);
- spin_lock_init(&dpu_kms->irq_obj.cb_lock); 
-
  	/* Create irq callbacks for all possible irq_idx */
  	dpu_kms->irq_obj.total_irqs = dpu_kms->hw_intr->total_irqs;
  	dpu_kms->irq_obj.irq_cb_tbl = kcalloc(dpu_kms->irq_obj.total_irqs,
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c
index bf9a147ac245..996011e356f7 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c
@@ -211,10 +211,9 @@ static void dpu_hw_intr_dispatch_irq(struct dpu_hw_intr *intr,
  	spin_unlock_irqrestore(&intr->irq_lock, irq_flags);
  }
-static int dpu_hw_intr_enable_irq(struct dpu_hw_intr *intr, int irq_idx) 
+static int dpu_hw_intr_enable_irq_locked(struct dpu_hw_intr *intr, int irq_idx)
  {
  	int reg_idx;
-	unsigned long irq_flags;
  	const struct dpu_intr_reg *reg;
  	const char *dbgstr = NULL;
  	uint32_t cache_irq_mask;
@@ -227,10 +226,16 @@ static int dpu_hw_intr_enable_irq(struct dpu_hw_intr *intr, int irq_idx)
  		return -EINVAL;
  	}
+ /* 
+	 * The cache_irq_mask and hardware RMW operations needs to be done
+	 * under irq_lock and it's the caller's responsibility to ensure that's
+	 * held.
+	 */
+	assert_spin_locked(&intr->irq_lock);
+
  	reg_idx = DPU_IRQ_REG(irq_idx);
  	reg = &dpu_intr_set[reg_idx];
- spin_lock_irqsave(&intr->irq_lock, irq_flags); 
  	cache_irq_mask = intr->cache_irq_mask[reg_idx];
  	if (cache_irq_mask & DPU_IRQ_MASK(irq_idx)) {
  		dbgstr = "DPU IRQ already set:";
@@ -248,7 +253,6 @@ static int dpu_hw_intr_enable_irq(struct dpu_hw_intr *intr, int irq_idx)
intr->cache_irq_mask[reg_idx] = cache_irq_mask; 
  	}
-	spin_unlock_irqrestore(&intr->irq_lock, irq_flags);
pr_debug("%s MASK:0x%.8lx, CACHE-MASK:0x%.8x\n", dbgstr, 
  			DPU_IRQ_MASK(irq_idx), cache_irq_mask);
@@ -256,7 +260,7 @@ static int dpu_hw_intr_enable_irq(struct dpu_hw_intr *intr, int irq_idx)
  	return 0;
  }
-static int dpu_hw_intr_disable_irq_nolock(struct dpu_hw_intr *intr, int irq_idx) 
+static int dpu_hw_intr_disable_irq_locked(struct dpu_hw_intr *intr, int irq_idx)
  {
  	int reg_idx;
  	const struct dpu_intr_reg *reg;
@@ -271,6 +275,13 @@ static int dpu_hw_intr_disable_irq_nolock(struct dpu_hw_intr *intr, int irq_idx)
  		return -EINVAL;
  	}
+ /* 
+	 * The cache_irq_mask and hardware RMW operations needs to be done
+	 * under irq_lock and it's the caller's responsibility to ensure that's
+	 * held.
+	 */
+	assert_spin_locked(&intr->irq_lock);
+
  	reg_idx = DPU_IRQ_REG(irq_idx);
  	reg = &dpu_intr_set[reg_idx];
@@ -298,25 +309,6 @@ static int dpu_hw_intr_disable_irq_nolock(struct dpu_hw_intr *intr, int irq_idx) 
  	return 0;
  }
-static int dpu_hw_intr_disable_irq(struct dpu_hw_intr *intr, int irq_idx) 
-{
-	unsigned long irq_flags;
-
-	if (!intr)
-		return -EINVAL;
-
-	if (irq_idx < 0 || irq_idx >= intr->total_irqs) {
-		pr_err("invalid IRQ index: [%d]\n", irq_idx);
-		return -EINVAL;
-	}
-
-	spin_lock_irqsave(&intr->irq_lock, irq_flags);
-	dpu_hw_intr_disable_irq_nolock(intr, irq_idx);
-	spin_unlock_irqrestore(&intr->irq_lock, irq_flags);
-
-	return 0;
-}
-
  static int dpu_hw_intr_clear_irqs(struct dpu_hw_intr *intr)
  {
  	int i;
@@ -388,14 +380,30 @@ static u32 dpu_hw_intr_get_interrupt_status(struct dpu_hw_intr *intr,
  	return intr_status;
  }
+static unsigned long dpu_hw_intr_lock(struct dpu_hw_intr *intr) 
+{
+	unsigned long irq_flags;
+
+	spin_lock_irqsave(&intr->irq_lock, irq_flags);
+
+	return irq_flags;
+}
+
+static void dpu_hw_intr_unlock(struct dpu_hw_intr *intr, unsigned long irq_flags)
+{
+	spin_unlock_irqrestore(&intr->irq_lock, irq_flags);
+}
+
  static void __setup_intr_ops(struct dpu_hw_intr_ops *ops)
  {
-	ops->enable_irq = dpu_hw_intr_enable_irq;
-	ops->disable_irq = dpu_hw_intr_disable_irq;
+	ops->enable_irq_locked = dpu_hw_intr_enable_irq_locked;
+	ops->disable_irq_locked = dpu_hw_intr_disable_irq_locked;
  	ops->dispatch_irqs = dpu_hw_intr_dispatch_irq;
  	ops->clear_all_irqs = dpu_hw_intr_clear_irqs;
  	ops->disable_all_irqs = dpu_hw_intr_disable_irqs;
  	ops->get_interrupt_status = dpu_hw_intr_get_interrupt_status;
+	ops->lock = dpu_hw_intr_lock;
+	ops->unlock = dpu_hw_intr_unlock;
  }
static void __intr_offset(struct dpu_mdss_cfg *m, 
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.h
index 0073d32effc5..d90dac77c26f 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.h
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.h
@@ -46,7 +46,7 @@ struct dpu_hw_intr_ops {
  	 * @irq_idx:	Lookup irq index return from irq_idx_lookup
  	 * @return:	0 for success, otherwise failure
  	 */
-	int (*enable_irq)(
+	int (*enable_irq_locked)(
  			struct dpu_hw_intr *intr,
  			int irq_idx);
@@ -56,7 +56,7 @@ struct dpu_hw_intr_ops { 
  	 * @irq_idx:	Lookup irq index return from irq_idx_lookup
  	 * @return:	0 for success, otherwise failure
  	 */
-	int (*disable_irq)(
+	int (*disable_irq_locked)(
  			struct dpu_hw_intr *intr,
  			int irq_idx);
@@ -101,6 +101,22 @@ struct dpu_hw_intr_ops { 
  			struct dpu_hw_intr *intr,
  			int irq_idx,
  			bool clear);
+
+	/**
+	 * lock - take the IRQ lock
+	 * @intr:	HW interrupt handle
+	 * @return:	irq_flags for the taken spinlock
+	 */
+	unsigned long (*lock)(
+			struct dpu_hw_intr *intr);
+
+	/**
+	 * unlock - take the IRQ lock
+	 * @intr:	HW interrupt handle
+	 * @irq_flags:  the irq_flags returned from lock
+	 */
+	void (*unlock)(
+			struct dpu_hw_intr *intr, unsigned long irq_flags);
  };
/** 
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
index f6840b1af6e4..3034da1d2977 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
@@ -82,14 +82,12 @@ struct dpu_irq_callback {
   * struct dpu_irq: IRQ structure contains callback registration info
   * @total_irq:    total number of irq_idx obtained from HW interrupts mapping
   * @irq_cb_tbl:   array of IRQ callbacks setting
- * @cb_lock:      callback lock
   * @debugfs_file: debugfs file for irq statistics
   */
  struct dpu_irq {
  	u32 total_irqs;
  	struct list_head *irq_cb_tbl;
  	atomic_t *irq_counts;
-	spinlock_t cb_lock;
  };
struct dpu_kms { 




--
With best wishes
Dmitry
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