linux-kernel - Re: [RFC PATCH 1/2] rcu: sysctl: Panic on RCU Stall

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Date:	Tue, 31 May 2016 19:49:41 -0300
From:	Daniel Bristot de Oliveira <daolivei@...hat.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	"Luis Claudio R. Goncalves" <lgoncalv@...hat.com>
Subject: Re: [RFC PATCH 1/2] rcu: sysctl: Panic on RCU Stall

On 05/31/2016 04:23 PM, Josh Triplett wrote:

Hi Josh,

> Sorry, realized something else a moment after sending: I don't think
> this will build if you use the tiny RCU implementation.  That
> implementation *does* support tracing, and if you enable tracing,
> you'll have CONFIG_RCU_STALL_COMMON=y, but you won't build tree.c where
> the variable definition lives.  So, the sysctl code will reference a
> variable that doesn't exist.

Good catch!

[root@f23 linux]# egrep '(TINY_RCU|RCU_TRACE)' .config
CONFIG_TINY_RCU=y
# CONFIG_TREE_RCU_TRACE is not set
CONFIG_RCU_TRACE=y
[root@f23 linux]# make
...
kernel/built-in.o:(.data+0x4688): undefined reference to `sysctl_panic_on_rcu_stall'
Makefile:937: recipe for target 'vmlinux' failed
make: *** [vmlinux] Error 1

How about this change in the condition:
-#ifdef CONFIG_RCU_STALL_COMMON
+#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)

It worked fine here, but I may be missing something, so I better
check with the experts :-).

Thanks for reviewing the patch set!

-- Daniel