linux-kernel - [PATCH 2/2] lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus

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Date:   Mon, 10 May 2021 16:10:24 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Yejune Deng <yejune.deng@...il.com>, mingo@...nel.org,
        peterz@...radead.org, tglx@...utronix.de, bristot@...hat.com
Subject: [PATCH 2/2] lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed

From: Yejune Deng <yejune.deng@...il.com>

is_percpu_thread() more elegantly handles SMP vs UP, and further checks the
presence of PF_NO_SETAFFINITY. This lets us catch cases where
check_preemption_disabled() can race with a concurrent sched_setaffinity().

Signed-off-by: Yejune Deng <yejune.deng@...il.com>
[Amended changelog]
Signed-off-by: Valentin Schneider <valentin.schneider@....com>
---
 lib/smp_processor_id.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c
index 1c1dbd300325..046ac6297c78 100644
--- a/lib/smp_processor_id.c
+++ b/lib/smp_processor_id.c
@@ -19,11 +19,7 @@ unsigned int check_preemption_disabled(const char *what1, const char *what2)
 	if (irqs_disabled())
 		goto out;
 
-	/*
-	 * Kernel threads bound to a single CPU can safely use
-	 * smp_processor_id():
-	 */
-	if (current->nr_cpus_allowed == 1)
+	if (is_percpu_thread())
 		goto out;
 
 #ifdef CONFIG_SMP
-- 
2.25.1