linux-kernel - [PATCH 2/4] cpumask: make "all" alias global and not just RCU

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Date:   Sun,  8 Nov 2020 11:08:14 -0500
From:   Paul Gortmaker <paul.gortmaker@...driver.com>
To:     linux-kernel@...r.kernel.org
Cc:     cgroups@...r.kernel.org,
        Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [PATCH 2/4] cpumask: make "all" alias global and not just RCU

It is probably better that we don't have subsystem specific
abbreviations or aliases for generic CPU list specifications.

Hence we move the "all" from RCU out to lib/ so that it can be
used in any instance where CPU lists are being parsed.

Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 Documentation/admin-guide/kernel-parameters.rst |  7 +++++++
 Documentation/admin-guide/kernel-parameters.txt |  4 +---
 kernel/rcu/tree_plugin.h                        | 13 ++++---------
 lib/cpumask.c                                   |  6 ++++++
 4 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
index 6d421694d98e..ef98ca700946 100644
--- a/Documentation/admin-guide/kernel-parameters.rst
+++ b/Documentation/admin-guide/kernel-parameters.rst
@@ -68,6 +68,13 @@ For example one can add to the command line following parameter:
 
 where the final item represents CPUs 100,101,125,126,150,151,...
 
+The following convenience aliases are also accepted and used:
+
+        foo_cpus=all
+
+is equivalent to "foo_cpus=0-N" -- where "N" is the numerically last CPU on
+the system, thus avoiding looking up the value in "/sys/devices/system/cpu"
+in advance on each deployed system.
 
 
 This document may not be entirely up to date and comprehensive. The command
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 526d65d8573a..96eed72f02a2 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4023,9 +4023,7 @@
 				see CONFIG_RAS_CEC help text.
 
 	rcu_nocbs=	[KNL]
-			The argument is a cpu list, as described above,
-			except that the string "all" can be used to
-			specify every CPU on the system.
+			The argument is a cpu list, as described above.
 
 			In kernels built with CONFIG_RCU_NOCB_CPU=y, set
 			the specified list of CPUs to be no-callback CPUs.
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index fd8a52e9a887..b18f89f94fd3 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1463,20 +1463,15 @@ static void rcu_cleanup_after_idle(void)
 
 /*
  * 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.
+ * If the list is invalid, a warning is emitted and all CPUs are offloaded.
  */
 static int __init rcu_nocb_setup(char *str)
 {
 	alloc_bootmem_cpumask_var(&rcu_nocb_mask);
-	if (!strcasecmp(str, "all"))
+	if (cpulist_parse(str, rcu_nocb_mask)) {
+		pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
 		cpumask_setall(rcu_nocb_mask);
-	else
-		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);
diff --git a/lib/cpumask.c b/lib/cpumask.c
index 5eb002237404..15599cdf5db6 100644
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -2,6 +2,7 @@
 #include <linux/slab.h>
 #include <linux/kernel.h>
 #include <linux/bitops.h>
+#include <linux/string.h>
 #include <linux/cpumask.h>
 #include <linux/export.h>
 #include <linux/memblock.h>
@@ -104,6 +105,11 @@ EXPORT_SYMBOL(cpumask_next_wrap);
  */
 int cpulist_parse(const char *buf, struct cpumask *dstp)
 {
+	if (!strcmp(buf, "all")) {
+		cpumask_setall(dstp);
+		return 0;
+	}
+
 	return bitmap_parselist(buf, cpumask_bits(dstp), nr_cpumask_bits);
 }
 EXPORT_SYMBOL(cpulist_parse);
-- 
2.25.1