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From:   Jun Miao <jun.miao@windriver.com>
To:     airlied@linux.ie, daniel@ffwll.ch
Cc:     jani.nikula@linux.intel.com, intel-gfx@lists.freedesktop.org,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: [V3] drm/i915/gt: Fix a lockdep warning with interrupts enabled
Date:   Fri, 16 Apr 2021 17:08:52 +0800
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Don`t simplely disable local interrupt delivery of CPU hardware irq, should race
the region inside signal_irq_work, include intel_breadcrumbs_disarm_irq/intel_breadcrumbs_arm_irq.

RT complains about might sleep inside signal_irq_work() because spin_lock will
be invoked after disabling interrupts.

Thanks to Tvrtko Ursulin for his expert opinions and suggestions.

BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:969
  #0: ffff89c4c00ca970 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x1cf/0x6d0
  #1: ffffa433c1f53e60 ((work_completion)(&engine->retire_work)){+.+.}-{0:0}, at: process_one_work+0x1cf 0x6d
  #2: ffff89c4ccb0a0a8 (kernel_context){+.+.}-{0:0}, at: engine_retire+0x62/0x110 [i915]
  #3: ffff89c4cf682300 (wakeref.mutex#3){+.+.}-{0:0}, at: __intel_wakeref_put_last+0x20/0x60 [i915]
  #4: ffff89c4ccb08398 (&b->irq_lock){+.+.}-{0:0}, at: intel_breadcrumbs_disarm_irq+0x20/0xd0 [i915]
 irq event stamp: 2126
 hardirqs last  enabled at (2125): [<ffffffffbb134739>] cancel_delayed_work+0xa9/0xc0
 hardirqs last disabled at (2126): [<ffffffffc0507fe6>] __intel_breadcrumbs_park+0x76/0x80 [i915]
 softirqs last  enabled at (0): [<ffffffffbb1099ce>] copy_process+0x63e/0x1630
 softirqs last disabled at (0): [<0000000000000000>] 0x0
 CPU: 3 PID: 281 Comm: kworker/3:3 Not tainted 5.10.27-rt34-yocto-preempt-rt #1
 Hardware name: Intel(R) Client Systems NUC7i5DNKE/NUC7i5DNB, BIOS DNKBLi5v.86A.0064.2019.0523.1933 05/23 2019
 Workqueue: events engine_retire [i915]
 Call Trace:
  show_stack+0x52/0x58
  dump_stack+0x7d/0x9f
  ___might_sleep.cold+0xe3/0xf4
  rt_spin_lock+0x3f/0xc0
  ? intel_breadcrumbs_disarm_irq+0x20/0xd0 [i915]
  intel_breadcrumbs_disarm_irq+0x20/0xd0 [i915]
  signal_irq_work+0x241/0x660 [i915]
  ? __this_cpu_preempt_check+0x13/0x20
  ? lockdep_hardirqs_off+0x106/0x120
  __intel_breadcrumbs_park+0x3f/0x80 [i915]
  __engine_park+0xbd/0xe0 [i915]
  ____intel_wakeref_put_last+0x22/0x60 [i915]
  __intel_wakeref_put_last+0x50/0x60 [i915]
  intel_context_exit_engine+0x5f/0x70 [i915]
  i915_request_retire+0x139/0x2d0 [i915]
  engine_retire+0xb0/0x110 [i915]
  process_one_work+0x26d/0x6d0
  worker_thread+0x53/0x330
  kthread+0x1b0/0x1d0
  ? process_one_work+0x6d0/0x6d0
  ? __kthread_parkme+0xc0/0xc0
  ret_from_fork+0x22/0x30

Fixes: 9d5612ca165a ("drm/i915/gt: Defer enabling the breadcrumb interrupt to after submission")
Signed-off-by: Jun Miao <jun.miao@windriver.com>
---
 drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
index 34a645d..01eb18e 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
@@ -82,13 +82,15 @@ static void __intel_breadcrumbs_arm_irq(struct intel_breadcrumbs *b)
 
 static void intel_breadcrumbs_arm_irq(struct intel_breadcrumbs *b)
 {
+	unsigned long flags;
+
 	if (!b->irq_engine)
 		return;
 
-	spin_lock(&b->irq_lock);
+	spin_lock_irqsave(&b->irq_lock, flags);
 	if (!b->irq_armed)
 		__intel_breadcrumbs_arm_irq(b);
-	spin_unlock(&b->irq_lock);
+	spin_unlock_irqrestore(&b->irq_lock, flags);
 }
 
 static void __intel_breadcrumbs_disarm_irq(struct intel_breadcrumbs *b)
@@ -103,10 +105,12 @@ static void __intel_breadcrumbs_disarm_irq(struct intel_breadcrumbs *b)
 
 static void intel_breadcrumbs_disarm_irq(struct intel_breadcrumbs *b)
 {
-	spin_lock(&b->irq_lock);
+	unsigned long flags;
+
+	spin_lock_irqsave(&b->irq_lock, flags);
 	if (b->irq_armed)
 		__intel_breadcrumbs_disarm_irq(b);
-	spin_unlock(&b->irq_lock);
+	spin_unlock_irqrestore(&b->irq_lock, flags);
 }
 
 static void add_signaling_context(struct intel_breadcrumbs *b,
@@ -200,6 +204,7 @@ static void signal_irq_work(struct irq_work *work)
 	const ktime_t timestamp = ktime_get();
 	struct llist_node *signal, *sn;
 	struct intel_context *ce;
+	unsigned long flags;
 
 	signal = NULL;
 	if (unlikely(!llist_empty(&b->signaled_requests)))
@@ -278,11 +283,11 @@ static void signal_irq_work(struct irq_work *work)
 			llist_entry(signal, typeof(*rq), signal_node);
 		struct list_head cb_list;
 
-		spin_lock(&rq->lock);
+		spin_lock_irqsave(&rq->lock, flags);
 		list_replace(&rq->fence.cb_list, &cb_list);
 		__dma_fence_signal__timestamp(&rq->fence, timestamp);
 		__dma_fence_signal__notify(&rq->fence, &cb_list);
-		spin_unlock(&rq->lock);
+		spin_unlock_irqrestore(&rq->lock, flags);
 
 		i915_request_put(rq);
 	}
@@ -337,9 +342,7 @@ void __intel_breadcrumbs_park(struct intel_breadcrumbs *b)
 	/* Kick the work once more to drain the signalers, and disarm the irq */
 	irq_work_sync(&b->irq_work);
 	while (READ_ONCE(b->irq_armed) && !atomic_read(&b->active)) {
-		local_irq_disable();
 		signal_irq_work(&b->irq_work);
-		local_irq_enable();
 		cond_resched();
 	}
 }
-- 
2.7.4