[tip: sched/core] lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed

[tip-bot2 for Yejune Deng]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     570a752b7a9bd03b50ad6420cd7f10092cc11bd3
Gitweb:        https://git.kernel.org/tip/570a752b7a9bd03b50ad6420cd7f10092cc11bd3
Author:        Yejune Deng <yejune.deng@xxxxxxxxx>
AuthorDate:    Mon, 10 May 2021 16:10:24 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Wed, 19 May 2021 10:51:40 +02:00

lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed

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@xxxxxxxxx>
[Amended changelog]
Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20210510151024.2448573-3-valentin.schneider@xxxxxxx
---
 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 1c1dbd3..046ac62 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