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

From: Josh Triplett
Date: Mon Jan 07 2013 - 10:58:04 EST

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@xxxxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>

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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