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

[Dmitry Baryshkov]

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