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Date:   Thu, 23 Jun 2022 15:47:10 +0200
From:   Juri Lelli <juri.lelli@redhat.com>
To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     linux-rt-users <linux-rt-users@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RT] WARNING at hrtimer_start_range_ns
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On 23/06/22 12:46, Sebastian Andrzej Siewior wrote:
> On 2022-06-15 16:53:55 [+0200], Juri Lelli wrote:
> > Hi,
> Hi,
> 
> > My understanding is that we have
> > 
> > fs/aio.c::read_events
> >   wait_event_interruptible_hrtimeout
> >     __wait_event_hrtimeout
> >       hrtimer_init_sleeper_on_stack <- this might mode |=HRTIMER_MODE_HARD on RT
> 
> will set HRTIMER_MODE_HARD  of might set HRTIMER_MODE_HARD if the task has elevated priority
> (RT/DL).
> 
> >         hrtimer_start_range_ns
> > 	  WARN_ON_ONCE(!(mode & HRTIMER_MODE_HARD) ^ !timer->is_hard)
> > 	  fires since the latter doesn't see the change of mode done by
> > 	  init_sleeper
> 
> correct.
> 
> > The attached patch seems to cure the problem, although I'm not entirely
> > sure it's the cleanest fix (if I'm right at all about it :).
> 
> The problem seems to be that __wait_event_hrtimeout() does
> hrtimer_start_range_ns() instead of hrtimer_sleeper_start_expires(). So
> if you switch that, then it should go away.

Ah, indeed. That looks simpler. :)

Will test and put a v2 together.

Thanks!
Juri