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From: Daniel Bristot de Oliveira <daolivei@redhat.com>
X-Google-Original-From: Daniel Bristot de Oliveira <bristot@redhat.com>
Subject: Re: [RFC PATCH 1/2] rcu: sysctl: Panic on RCU Stall
To: Josh Triplett <josh@joshtriplett.org>
References: <cover.1464652607.git.bristot@redhat.com>
 <fba2e213f572f16d8915d709f19c368f04ebdb93.1464652607.git.bristot@redhat.com>
 <20160531191827.GA4574@x> <20160531192325.GA4851@x>
Cc: linux-kernel@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        "Luis Claudio R. Goncalves" <lgoncalv@redhat.com>
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Date: Tue, 31 May 2016 19:49:41 -0300
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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