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

[Tvrtko Ursulin]

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?

> 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 at windriver.com>
> ---
>   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.

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

Regards,

Tvrtko

>   		cond_resched();
>   	}
>   }
>