linux-kernel - Re: [PATCH tip/core/rcu 1/1] Tiny RCU changes for 3.9

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Message-ID: <20130107155810.GC11145@leaf>
Date:	Mon, 7 Jan 2013 07:58:10 -0800
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...icios.com, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, edumazet@...gle.com, darren@...art.com,
	fweisbec@...il.com, sbw@....edu, patches@...aro.org
Subject: Re: [PATCH tip/core/rcu 1/1] Tiny RCU changes for 3.9

On Sat, Jan 05, 2013 at 09:50:59AM -0800, Paul E. McKenney wrote:
> rcu: Provide RCU CPU stall warnings for tiny RCU
> 
> Tiny RCU has historically omitted RCU CPU stall warnings in order to
> reduce memory requirements, however, lack of these warnings caused Thomas
> Gleixner some debugging pain recently.  Therefore, this commit adds RCU
> CPU stall warnings to tiny RCU if RCU_TRACE=y.  This keeps the memory
> footprint small, while still enabling CPU stall warnings in kernels
> built to enable them.
> 
> This is still a bit on the high-risk side, so running this will likely
> be a debugging exercise.
> 
> Reported-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

Did you generate this patch with something other than git?  The
formatting seems a bit off: it doesn't have a diffstat or the usual
"---" line between the commit message and the patch.

This patch seems reasonable to me, but the repeated use of #if
defined(CONFIG_SMP) || defined(CONFIG_RCU_TRACE) seems somewhat
annoying, and fragile if you ever decide to change the conditions.  How
about defining an appropriate symbol in Kconfig for stall warnings, and
using that?

- Josh Triplett
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