From: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
To: Bjorn Andersson <bjorn.andersson@linaro.org>,
Rob Clark <robdclark@gmail.com>, Sean Paul <sean@poorly.run>,
David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
Abhinav Kumar <abhinavk@codeaurora.org>
Cc: linux-arm-msm@vger.kernel.org, freedreno@lists.freedesktop.org,
linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] drm/msm/dpu: Avoid ABBA deadlock between IRQ modules
Date: Thu, 10 Jun 2021 14:46:00 +0300 [thread overview]
Message-ID: <faf0dbb2-a219-51fe-5cbd-752848a0286f@linaro.org> (raw)
In-Reply-To: <20210609231507.3031904-1-bjorn.andersson@linaro.org>
On 10/06/2021 02:15, 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, serialize the
> register/unregister operations under a single mutex.
>
> Fixes: 1c1e7763a6d4 ("drm/msm/dpu: simplify IRQ enabling/disabling")
> Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
I have been thinking about this for quite some time. I'm still not
confident about the proposed scheme.
What more intrusive, but more obvious change:
- Drop dpu_kms->irq_obj.cb_lock alltogether. Use hw_intr's irq_lock
instead in the register/unregister path and no locks in the callback itself.
- Do not take locks in the dpu_hw_intr_enable_irq/disable_irq (as we
are already locked outside).
The core_irq is the only user of the hw_intr framework. In fact I'd like
to squash them together at some point (if I get some time, I'll send
patches during this cycle).
> ---
> drivers/gpu/drm/msm/disp/dpu1/dpu_core_irq.c | 10 +++++++---
> drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h | 2 ++
> 2 files changed, 9 insertions(+), 3 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..62bbe35eff7b 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_core_irq.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_core_irq.c
> @@ -82,11 +82,13 @@ 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);
>
> + mutex_lock(&dpu_kms->irq_obj.hw_enable_lock);
> spin_lock_irqsave(&dpu_kms->irq_obj.cb_lock, irq_flags);
> trace_dpu_core_irq_register_callback(irq_idx, register_irq_cb);
> list_del_init(®ister_irq_cb->list);
> list_add_tail(®ister_irq_cb->list,
> &dpu_kms->irq_obj.irq_cb_tbl[irq_idx]);
> + spin_unlock_irqrestore(&dpu_kms->irq_obj.cb_lock, irq_flags);
> if (list_is_first(®ister_irq_cb->list,
> &dpu_kms->irq_obj.irq_cb_tbl[irq_idx])) {
> int ret = dpu_kms->hw_intr->ops.enable_irq(
> @@ -96,8 +98,7 @@ int dpu_core_irq_register_callback(struct dpu_kms *dpu_kms, int irq_idx,
> DPU_ERROR("Fail to enable IRQ for irq_idx:%d\n",
> irq_idx);
> }
> -
> - spin_unlock_irqrestore(&dpu_kms->irq_obj.cb_lock, irq_flags);
> + mutex_unlock(&dpu_kms->irq_obj.hw_enable_lock);
>
> return 0;
> }
> @@ -127,9 +128,11 @@ 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);
>
> + mutex_lock(&dpu_kms->irq_obj.hw_enable_lock);
> spin_lock_irqsave(&dpu_kms->irq_obj.cb_lock, irq_flags);
> trace_dpu_core_irq_unregister_callback(irq_idx, register_irq_cb);
> list_del_init(®ister_irq_cb->list);
> + spin_unlock_irqrestore(&dpu_kms->irq_obj.cb_lock, irq_flags);
> /* 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(
> @@ -140,7 +143,7 @@ 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);
> + mutex_unlock(&dpu_kms->irq_obj.hw_enable_lock);
>
> return 0;
> }
> @@ -207,6 +210,7 @@ void dpu_core_irq_preinstall(struct dpu_kms *dpu_kms)
> dpu_disable_all_irqs(dpu_kms);
> pm_runtime_put_sync(&dpu_kms->pdev->dev);
>
> + mutex_init(&dpu_kms->irq_obj.hw_enable_lock);
> spin_lock_init(&dpu_kms->irq_obj.cb_lock);
>
> /* Create irq callbacks for all possible irq_idx */
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
> index f6840b1af6e4..5a162caea29d 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
> @@ -83,6 +83,7 @@ struct dpu_irq_callback {
> * @total_irq: total number of irq_idx obtained from HW interrupts mapping
> * @irq_cb_tbl: array of IRQ callbacks setting
> * @cb_lock: callback lock
> + * @hw_enable_lock: lock to synchronize callback register and unregister
> * @debugfs_file: debugfs file for irq statistics
> */
> struct dpu_irq {
> @@ -90,6 +91,7 @@ struct dpu_irq {
> struct list_head *irq_cb_tbl;
> atomic_t *irq_counts;
> spinlock_t cb_lock;
> + struct mutex hw_enable_lock;
> };
>
> struct dpu_kms {
>
--
With best wishes
Dmitry
next prev parent reply other threads:[~2021-06-10 11:46 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-09 23:15 [PATCH] drm/msm/dpu: Avoid ABBA deadlock between IRQ modules Bjorn Andersson
2021-06-10 11:46 ` Dmitry Baryshkov [this message]
2021-06-10 14:44 ` Bjorn Andersson
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