From b81dce77cedcea6f00292f02d4b1ebbfc2c5988d Mon Sep 17 00:00:00 2001
From: Sander Vanheule <sander@svanheule.net>
Date: Sat, 2 Jul 2022 18:08:25 +0200
Subject: cpumask: Fix invalid uniprocessor mask assumption

On uniprocessor builds, any CPU mask is assumed to contain exactly one CPU
(cpu0).  This assumption ignores the existence of empty masks, resulting
in incorrect behaviour.

cpumask_first_zero(), cpumask_next_zero(), and for_each_cpu_not() don't
provide behaviour matching the assumption that a UP mask is always "1",
and instead provide behaviour matching the empty mask.

Drop the incorrectly optimised code and use the generic implementations in
all cases.

Link: https://lkml.kernel.org/r/86bf3f005abba2d92120ddd0809235cab4f759a6.1656777646.git.sander@svanheule.net
Signed-off-by: Sander Vanheule <sander@svanheule.net>
Suggested-by: Yury Norov <yury.norov@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Marco Elver <elver@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 lib/cpumask.c | 2 ++
 1 file changed, 2 insertions(+)

(limited to 'lib/cpumask.c')

diff --git a/lib/cpumask.c b/lib/cpumask.c
index a971a82d2f43..b9728513a4d4 100644
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -192,6 +192,7 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask)
 }
 #endif
 
+#if NR_CPUS > 1
 /**
  * cpumask_local_spread - select the i'th cpu with local numa cpu's first
  * @i: index number
@@ -279,3 +280,4 @@ int cpumask_any_distribute(const struct cpumask *srcp)
 	return next;
 }
 EXPORT_SYMBOL(cpumask_any_distribute);
+#endif /* NR_CPUS */
-- 
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