linux-kernel - [PATCH 10/16] sched: optimize __set_cpus_allowed_ptr

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Date:   Mon, 18 Jul 2022 12:28:38 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     linux-kernel@...r.kernel.org,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Alexey Klimov <aklimov@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Ben Segall <bsegall@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dennis Zhou <dennis@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Eric Dumazet <edumazet@...gle.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Ingo Molnar <mingo@...hat.com>,
        Isabella Basso <isabbasso@...eup.net>,
        John Fastabend <john.fastabend@...il.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        KP Singh <kpsingh@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Martin KaFai Lau <kafai@...com>,
        Mel Gorman <mgorman@...e.de>, Miroslav Benes <mbenes@...e.cz>,
        Nathan Chancellor <nathan@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Song Liu <songliubraving@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tejun Heo <tj@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <vschneid@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Vlastimil Babka <vbabka@...e.cz>, Yonghong Song <yhs@...com>,
        Yury Norov <yury.norov@...il.com>, linux-mm@...ck.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH 10/16] sched: optimize __set_cpus_allowed_ptr_locked()

Don't call cpumask_subset(new_mask, cpu_allowed_mask) if new_mask
is cpu_allowed_mask.

Caught with CONFIG_DEBUG_BITMAP:
[    0.132174] Call trace:
[    0.132189]  __bitmap_check_params+0x144/0x250
[    0.132216]  __set_cpus_allowed_ptr_locked+0x8c/0x2c0
[    0.132241]  sched_init_smp+0x80/0xd8
[    0.132273]  kernel_init_freeable+0x12c/0x28c
[    0.132299]  kernel_init+0x28/0x13c
[    0.132325]  ret_from_fork+0x10/0x20
[    0.132354] ---[ end trace 0000000000000000 ]---
[    0.132378] b1:	ffffcd0c07819a58
[    0.132388] b2:	ffffcd0c07819a58
[    0.132397] b3:	0
[    0.132405] nbits:	256
[    0.132414] start:	0
[    0.132422] off:	0
[    0.132444] Bitmap: parameters check failed
[    0.132467] include/linux/bitmap.h [468]: bitmap_subset

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 kernel/sched/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index da0bf6fe9ecd..d6424336ef2d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2874,7 +2874,8 @@ static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
 		cpu_valid_mask = cpu_online_mask;
 	}
 
-	if (!kthread && !cpumask_subset(new_mask, cpu_allowed_mask)) {
+	if (!kthread && new_mask != cpu_allowed_mask &&
+			!cpumask_subset(new_mask, cpu_allowed_mask)) {
 		ret = -EINVAL;
 		goto out;
 	}
-- 
2.34.1