linux-kernel - Re: [PATCH 5.10-rt+] drm/i915/gt: transform irq_disable into local

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Message-ID: <20211009164908.GA21269@zipoli.concurrent-rt.com>
Date:   Sat, 9 Oct 2021 12:49:08 -0400
From:   Joe Korty <joe.korty@...current-rt.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Clark Williams <williams@...hat.com>,
        Jun Miao <jun.miao@...driver.com>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5.10-rt+] drm/i915/gt: transform irq_disable into
 local_lock.

On Thu, Oct 07, 2021 at 07:19:29PM +0200, Sebastian Andrzej Siewior wrote:
> On 2021-10-07 12:59:28 [-0400], Joe Korty wrote:
> > Convert IRQ blocking in intel_breadcrumbs_park() to a local lock.
> > 
> > Affects 5.10-rt and all later releases, up to and including when
> > rt was merged into mainline.
> 
> RT was merged into mainline? Nobody tells me anything anymore??? 
> 
> > This problem has been reported in two other linux-rt-users postings,
> >   
> >    [PREEMPT_RT] i915: fix PREEMPT_RT locking splats (Clark Williams)
> >    [linux-5.12.y-rt] drm/i915/gt: Fix a lockdep warning with interrupts enabled (Jun Miao)
> > 
> > Neither of these submit the obvious solution, nor,
> > AFAICT, has either yet been acted on.  So I muddy the
> > waters further by submitting this, a third fix.
> 
> 5.12 is longer maintained. Could you please take the latest devel tree
> for testing and participate in
>   https://lore.kernel.org/all/20211005150046.1000285-1-bigeasy@linutronix.de/
> 
> If anything I would prefer those patches backported into v5.10 if it is
> affected.


Hi Sebastian,
Please add my 'Tested-by' to the below patch.  

   [linux-5.12.y-rt] drm/i915/gt: Fix a lockdep warning with interrupts enabled (Jun Miao)

What was tested was a backport to 5.10-rt.  One reject
was encountered, trivially resolved.  No other adjustments
were made.

My regression tests of last night all passed without any
of the usual lockdep splats occuring.  Prior to this,
I could be assured of a large enough flood of splats to
overwhelm the kernel log.

My test stand is a Supermicro C7Z170-SQ.  This is tthe
only system I have on which I could trigger the problem.

I could not find this patch in the 5.12-rt or the 5.15-rt
tree, so I fetched a copy out of the linux-rt-users
archives, and backported that.

Tested-by: Joe Korty <joe.korty@...current-rt.com>