Re: [PATCH][V2] drm/i915/gt: Fix a lockdep warning on RT kernel

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On 4/15/21 7:12 PM, Tvrtko Ursulin wrote:
[Please note: This e-mail is from an EXTERNAL e-mail address]

Hi,

On 14/04/2021 15:48, Jun Miao wrote:
Don`t simple disable all the HD-irq, should race the region in the
intel_breadcrumbs_disarm_irq() only.


What is HD-irq, I am, not familiar with that term?

Disable local interrupt delivery from Hardware of cpu.:-)

Thanks,

Jun


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@xxxxxxxxxxxxx>
---
  drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 8 ++++----
  1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
index 34a645d..0589b1a 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
@@ -103,10 +103,12 @@ 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,
@@ -337,9 +339,7 @@ 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();

Unfortunately there is another lock inside signal_irq_work (rq->lock)
which needs to be taken irq safe.

Ok, i will change the left spin_lock -> spin_lock_irqsave.

In fact,  inside signal_irq_work,  intel_breadcrumbs_arm_irq (&b->irq_lock)  which also needs to be taken irq safe.

Thanks,

Jun

RT patches are in tree or out of the tree these days?

I base on the mainline kernel tree, and this BUG warning will not happen.  But RT v5.10 will complain "BUG warning", so i want this patch will solve RT WARNING without affecting mainline performance in mainline tree.

Thanks,

Jun



Regards,

Tvrtko

              cond_resched();
      }
  }

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