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Date:   Tue, 26 Mar 2019 16:13:06 -0700
From:   "Paul E. McKenney" <>
        "Paul E. McKenney" <>
Subject: [PATCH tip/core/rcu 10/18] rcu: Report error for bad rcu_nocbs= parameter values

This commit prints a console message when cpulist_parse() reports a
bad list of CPUs, and sets all CPUs' bits in that case.  The reason for
setting all CPUs' bits is that this is the safe(r) choice for real-time
workloads, which would normally be the ones using the rcu_nocbs= kernel
boot parameter.  Either way, later RCU console log messages list the
actual set of CPUs whose RCU callbacks will be offloaded.

Signed-off-by: Paul E. McKenney <>
 kernel/rcu/tree_plugin.h | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index ed4a6dabf31d..f0aeb7416dcc 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1772,14 +1772,22 @@ static void zero_cpu_stall_ticks(struct rcu_data *rdp)
-/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
+ * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
+ * The string after the "rcu_nocbs=" is either "all" for all CPUs, or a
+ * comma-separated list of CPUs and/or CPU ranges.  If an invalid list is
+ * given, a warning is emitted and all CPUs are offloaded.
+ */
 static int __init rcu_nocb_setup(char *str)
 	if (!strcasecmp(str, "all"))
-		cpulist_parse(str, rcu_nocb_mask);
+		if (cpulist_parse(str, rcu_nocb_mask)) {
+			pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
+			cpumask_setall(rcu_nocb_mask);
+		}
 	return 1;
 __setup("rcu_nocbs=", rcu_nocb_setup);

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