linux-kernel - [PATCH 1/2] kthread: Switch to cpu_possible

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Message-Id: <20200527142909.23372-2-frederic@kernel.org>
Date:   Wed, 27 May 2020 16:29:08 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Chris Friesen <chris.friesen@...driver.com>,
        Jim Somerville <Jim.Somerville@...driver.com>
Subject: [PATCH 1/2] kthread: Switch to cpu_possible_mask

From: Marcelo Tosatti <mtosatti@...hat.com>

Next patch will switch unbound kernel threads mask to
housekeeping_cpumask(), a subset of cpu_possible_mask. So in order to
ease bisection, lets first switch kthreads default affinity from
cpu_all_mask to cpu_possible_mask.

It looks safe to do so as cpu_possible_mask seem to be initialized
at setup_arch() time, way before kthreadd is created.

Suggested-by: Frederic Weisbecker <frederic@...nel.org>
Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
Cc: Chris Friesen <chris.friesen@...driver.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Jim Somerville <Jim.Somerville@...driver.com>
Cc: Christoph Lameter <cl@...ux.com>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 kernel/kthread.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index bfbfa481be3a..788bec94aca7 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -360,7 +360,7 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
 		 * The kernel thread should not inherit these properties.
 		 */
 		sched_setscheduler_nocheck(task, SCHED_NORMAL, &param);
-		set_cpus_allowed_ptr(task, cpu_all_mask);
+		set_cpus_allowed_ptr(task, cpu_possible_mask);
 	}
 	kfree(create);
 	return task;
@@ -585,7 +585,7 @@ int kthreadd(void *unused)
 	/* Setup a clean context for our children to inherit. */
 	set_task_comm(tsk, "kthreadd");
 	ignore_signals(tsk);
-	set_cpus_allowed_ptr(tsk, cpu_all_mask);
+	set_cpus_allowed_ptr(tsk, cpu_possible_mask);
 	set_mems_allowed(node_states[N_MEMORY]);
 
 	current->flags |= PF_NOFREEZE;
-- 
2.26.2