linux-kernel - [PATCH 30/33] kthread: Add API to update preferred affinity on kthread runtime

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251013203146.10162-31-frederic@kernel.org>
Date: Mon, 13 Oct 2025 22:31:43 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	Michal Koutný <mkoutny@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Danilo Krummrich <dakr@...nel.org>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Gabriele Monaco <gmonaco@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Johannes Weiner <hannes@...xchg.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Marco Crivellari <marco.crivellari@...e.com>,
	Michal Hocko <mhocko@...e.com>,
	Muchun Song <muchun.song@...ux.dev>,
	Paolo Abeni <pabeni@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Phil Auld <pauld@...hat.com>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Simon Horman <horms@...nel.org>,
	Tejun Heo <tj@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vlastimil Babka <vbabka@...e.cz>,
	Waiman Long <longman@...hat.com>,
	Will Deacon <will@...nel.org>,
	cgroups@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-block@...r.kernel.org,
	linux-mm@...ck.org,
	linux-pci@...r.kernel.org,
	netdev@...r.kernel.org
Subject: [PATCH 30/33] kthread: Add API to update preferred affinity on kthread runtime

Kthreads can apply for a preferred affinity upon creation but they have
no means to update that preferred affinity after the first wake up.
kthread_affine_preferred() is optimized by assuming the kthread
is sleeping while applying the allowed cpumask.

Therefore introduce a new API to further update the preferred affinity.

It will be used by IRQ kthreads.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 include/linux/kthread.h |  1 +
 kernel/kthread.c        | 55 +++++++++++++++++++++++++++++++++++------
 2 files changed, 48 insertions(+), 8 deletions(-)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index c92c1149ee6e..a06cae7f2c55 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -86,6 +86,7 @@ void free_kthread_struct(struct task_struct *k);
 void kthread_bind(struct task_struct *k, unsigned int cpu);
 void kthread_bind_mask(struct task_struct *k, const struct cpumask *mask);
 int kthread_affine_preferred(struct task_struct *p, const struct cpumask *mask);
+int kthread_affine_preferred_update(struct task_struct *p, const struct cpumask *mask);
 int kthread_stop(struct task_struct *k);
 int kthread_stop_put(struct task_struct *k);
 bool kthread_should_stop(void);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index d36bdfbd004e..f3397cf7542a 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -322,17 +322,16 @@ EXPORT_SYMBOL_GPL(kthread_parkme);
 void __noreturn kthread_exit(long result)
 {
 	struct kthread *kthread = to_kthread(current);
+	struct cpumask *to_free = NULL;
 	kthread->result = result;
-	if (!list_empty(&kthread->affinity_node)) {
-		mutex_lock(&kthread_affinity_lock);
-		list_del(&kthread->affinity_node);
-		mutex_unlock(&kthread_affinity_lock);
 
-		if (kthread->preferred_affinity) {
-			kfree(kthread->preferred_affinity);
-			kthread->preferred_affinity = NULL;
-		}
+	scoped_guard(mutex, &kthread_affinity_lock) {
+		if (!list_empty(&kthread->affinity_node))
+			list_del_init(&kthread->affinity_node);
+		to_free = kthread->preferred_affinity;
+		kthread->preferred_affinity = NULL;
 	}
+	kfree(to_free);
 	do_exit(0);
 }
 EXPORT_SYMBOL(kthread_exit);
@@ -900,6 +899,46 @@ int kthread_affine_preferred(struct task_struct *p, const struct cpumask *mask)
 }
 EXPORT_SYMBOL_GPL(kthread_affine_preferred);
 
+/**
+ * kthread_affine_preferred_update - update a kthread's preferred affinity
+ * @p: thread created by kthread_create().
+ * @cpumask: new mask of CPUs (might not be online, must be possible) for @k
+ *           to run on.
+ *
+ * Update the cpumask of the desired kthread's affinity that was passed by
+ * a previous call to kthread_affine_preferred(). This can be called either
+ * before or after the first wakeup of the kthread.
+ *
+ * Returns 0 if the affinity has been applied.
+ */
+int kthread_affine_preferred_update(struct task_struct *p,
+				    const struct cpumask *mask)
+{
+	struct kthread *kthread = to_kthread(p);
+	cpumask_var_t affinity;
+	int ret = 0;
+
+	if (!zalloc_cpumask_var(&affinity, GFP_KERNEL))
+		return -ENOMEM;
+
+	scoped_guard(mutex, &kthread_affinity_lock) {
+		if (WARN_ON_ONCE(!kthread->preferred_affinity ||
+				 list_empty(&kthread->affinity_node))) {
+			ret = -EINVAL;
+			goto out;
+		}
+
+		cpumask_copy(kthread->preferred_affinity, mask);
+		kthread_fetch_affinity(kthread, affinity);
+		set_cpus_allowed_ptr(p, affinity);
+	}
+out:
+	free_cpumask_var(affinity);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(kthread_affine_preferred_update);
+
 static int kthreads_update_affinity(bool force)
 {
 	cpumask_var_t affinity;
-- 
2.51.0