linux-kernel - Re: [ANNOUNCE] v5.4.17-rt9

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Message-ID: <a6a9ba66-4e63-8156-2e49-291087d9e847@ccrma.stanford.edu>
Date:   Thu, 6 Feb 2020 22:13:46 -0800
From:   Fernando Lopez-Lezcano <nando@...ma.Stanford.EDU>
To:     Mike Galbraith <efault@....de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     nando@...ma.Stanford.EDU, LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [ANNOUNCE] v5.4.17-rt9

On 2/6/20 10:11 PM, Mike Galbraith wrote:
> On Thu, 2020-02-06 at 15:59 -0800, Fernando Lopez-Lezcano wrote:
>> On 2/4/20 8:58 AM, Sebastian Andrzej Siewior wrote:
>>> Dear RT folks!
>>>
>>> I'm pleased to announce the v5.4.17-rt9 patch set.
>>
>> Thanks!
>> I see a continuous stream of these:
> 
> (snips gripage)
> 
> Yup, d67739268cf0 annoys RT locking if lockdep is enabled.  The below
> shut it up for my i915 equipped lappy.

Wow, Mike, thanks!, will try it out and report...
(might take me a couple of days)

-- Fernando


> drm/i915/gt: use a LOCAL_IRQ_LOCK in __timeline_mark_lock()
> 
> Quoting drm/i915/gt: Mark up the nested engine-pm timeline lock as irqsafe
> 
>      We use a fake timeline->mutex lock to reassure lockdep that the timeline
>      is always locked when emitting requests. However, the use inside
>      __engine_park() may be inside hardirq and so lockdep now complains about
>      the mixed irq-state of the nested locked. Disable irqs around the
>      lockdep tracking to keep it happy.
> 
> This lockdep appeasement breaks RT because we take sleeping locks between
> __timeline_mark_lock()/unlock().  Use a LOCAL_IRQ_LOCK instead.
> 
> Signed-off-by: Mike Galbraith <efaukt@....de>
> ---
>   drivers/gpu/drm/i915/gt/intel_engine_pm.c |    7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> @@ -38,12 +38,15 @@ static int __engine_unpark(struct intel_
>   }
> 
>   #if IS_ENABLED(CONFIG_LOCKDEP)
> +#include <linux/locallock.h>
> +
> +static DEFINE_LOCAL_IRQ_LOCK(timeline_lock);
> 
>   static inline unsigned long __timeline_mark_lock(struct intel_context *ce)
>   {
>   	unsigned long flags;
> 
> -	local_irq_save(flags);
> +	local_lock_irqsave(timeline_lock, flags);
>   	mutex_acquire(&ce->timeline->mutex.dep_map, 2, 0, _THIS_IP_);
> 
>   	return flags;
> @@ -53,7 +56,7 @@ static inline void __timeline_mark_unloc
>   					  unsigned long flags)
>   {
>   	mutex_release(&ce->timeline->mutex.dep_map, 0, _THIS_IP_);
> -	local_irq_restore(flags);
> +	local_unlock_irqrestore(timeline_lock, flags);
>   }
> 
>   #else
> 
>