linux-kernel - Re: Possible issue with commit 4961b6e11825?

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Message-ID: <20151206023647.GX3430@ubuntu>
Date:	Sun, 6 Dec 2015 08:06:47 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	tglx@...utronix.de, peterz@...radead.org,
	preeti@...ux.vnet.ibm.com, mtosatti@...hat.com, fweisbec@...il.com,
	linux-kernel@...r.kernel.org, sasha.levin@...cle.com
Subject: Re: Possible issue with commit 4961b6e11825?

On 05-12-15, 11:01, Paul E. McKenney wrote:
> And it was getting lucky.  In a set of 24 two-hour runs (triple parallel)
> on an earlier commit (not 3497d206c4d9, no clue what I was thinking) got
> me two failed runs, for a total of 49 reports of one of RCU's grace-period
> kthreads being starved, no reports of rcutorture's kthreads being starved,
> and no hangs on shutdown.  So much lower failure rate, but still failures.
> 
> At this point, I am a bit disgusted with bisection, so my next test cycle
> (36 two-hour runs on a system capable of doing three concurrently) is on
> the most recent -rcu, but with CPU hotplug disabled.  If that shows failures,
> then I hammer 3497d206c4d9 hard.
> 
> Anyway, if you have any ideas as to what might be happening, please don't
> keep them a secret!

I can be the least helpful here (based on knowledge), but I am not
able to find a reason for this diff in 3497d206c4d9:

-       if (!hrtimer_callback_running(hr))
-               __hrtimer_start_range_ns(hr, cpuctx->hrtimer_interval,
-                                        0, HRTIMER_MODE_REL_PINNED, 0);
+       hrtimer_start(hr, cpuctx->hrtimer_interval, HRTIMER_MODE_REL_PINNED);

The commit talks *only* about s/__hrtimer_start_range_ns/hrtimer_start
but not at all on why !hrtimer_callback_running(hr) was removed.
Perhaps there was a reason :)

-- 
viresh
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