linux-kernel - Re: [PATCH] tick/broadcast-hrtimer : Fix suspicious RCU usage in idle loop

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Message-ID: <20150302145354.GM21418@twins.programming.kicks-ass.net>
Date:	Mon, 2 Mar 2015 15:53:54 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc:	tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tick/broadcast-hrtimer : Fix suspicious RCU usage in
 idle loop

On Thu, Feb 26, 2015 at 08:52:02AM +0530, Preeti U Murthy wrote:
> The hrtimer mode of broadcast queues hrtimers in the idle entry
> path so as to wakeup cpus in deep idle states. 

Callgraph please...

> hrtimer_{start/cancel}
> functions call into tracing which uses RCU. But it is not legal to call
> into RCU in cpuidle because it is one of the quiescent states. Hence
> protect this region with RCU_NONIDLE which informs RCU that the cpu
> is momentarily non-idle.

It it not clear to me that every user of bc_set_next() is from IDLE.
>From what I can tell it ends up being clockevents_program_event() and
that is called quite a lot.

Why is bc_set_next() a good function to annotate?
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