linux-kernel - [PATCH tip/core/rcu 11/11] rcu: Fix CONFIG_RCU_NOCB_CPU_ALL panic on machines with sparse CPU mask

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Message-Id: <1380072561-31134-11-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Tue, 24 Sep 2013 18:29:21 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
	sbw@....edu, Kirill Tkhai <tkhai@...dex.ru>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 11/11] rcu: Fix CONFIG_RCU_NOCB_CPU_ALL panic on machines with sparse CPU mask

From: Kirill Tkhai <tkhai@...dex.ru>

Some architectures have sparse cpu mask. UltraSparc's cpuinfo for example:

CPU0: online
CPU2: online

So, set only possible CPUs when CONFIG_RCU_NOCB_CPU_ALL is enabled.

Also, check that user passes right 'rcu_nocbs=' option.

Signed-off-by: Kirill Tkhai <tkhai@...dex.ru>
CC: Dipankar Sarma <dipankar@...ibm.com>
[ paulmck: Fix pr_info() issue noted by scripts/checkpatch.pl. ]
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcutree_plugin.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index c684f7a..1855d66 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -96,10 +96,15 @@ static void __init rcu_bootup_announce_oddness(void)
 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
 #ifdef CONFIG_RCU_NOCB_CPU_ALL
 	pr_info("\tOffload RCU callbacks from all CPUs\n");
-	cpumask_setall(rcu_nocb_mask);
+	cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
 	if (have_rcu_nocb_mask) {
+		if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
+			pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
+			cpumask_and(rcu_nocb_mask, cpu_possible_mask,
+				    rcu_nocb_mask);
+		}
 		cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
 		pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
 		if (rcu_nocb_poll)
-- 
1.8.1.5

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