linux-kernel - Re: [PATCH RT 3/3 - take two ] fix get_monotonic

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Date:	Sat, 25 Aug 2007 07:06:54 -0400
From:	fche@...hat.com (Frank Ch. Eigler)
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	john stultz <johnstul@...ibm.com>
Subject: Re: [PATCH RT 3/3 - take two ] fix get_monotonic_cycles for latency tracer


Steven Rostedt <rostedt@...dmis.org> writes:

> [...]
> +		 * [...] We don't need to grab
> +		 * any locks, we just keep trying until get all the
> +		 * calculations together in one state.
> +		 *
> +		 * In fact, we __cant__ grab any locks. This
> +		 * function is called from the latency_tracer which can
> +		 * be called anywhere. To grab any locks (including
> +		 * seq_locks) we risk putting ourselves into a deadlock.

Perhaps you could add a comment about why the loop, which appears
potentially infinite as written, avoids livelock.  (It looks rather
like a seqlock read loop.)

- FChE
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