linux-kernel - [RFC PATCH 3/8] workqueue: Set PF_NO_SETAFFINITY instead of kthread_bind

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Date:   Thu,  4 Aug 2022 16:41:30 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <jiangshan.ljs@...group.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Tejun Heo <tj@...nel.org>, Petr Mladek <pmladek@...e.com>,
        Michal Hocko <mhocko@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: [RFC PATCH 3/8] workqueue: Set PF_NO_SETAFFINITY instead of kthread_bind_mask()

From: Lai Jiangshan <jiangshan.ljs@...group.com>

kthread_bind_mask() can't work correctly if spurious wakeup
happens before kthread_bind_mask().

And a spuriously wakeup worker's cpumask can be possibly changed
by a userspace if worker_attach_to_pool() is called earlier than
kthread_bind_mask().

To avoid the problem caused by spurious wokeup, set PF_NO_SETAFFINITY
at the starting of workers where kthread_bind_mask() can't be used
and luckily workqueue code binds cpumask by itself, all it needs is
only PF_NO_SETAFFINITY.

Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: Tejun Heo <tj@...nel.org>,
Cc: Petr Mladek <pmladek@...e.com>
Cc: Michal Hocko <mhocko@...e.com>,
Cc: Peter Zijlstra <peterz@...radead.org>,
Cc: Wedson Almeida Filho <wedsonaf@...gle.com>
Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
---
 kernel/workqueue.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index f5b12c6778cc..82937c0fb21f 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1958,7 +1958,6 @@ static struct worker *create_worker(struct worker_pool *pool)
 		goto fail;
 
 	set_user_nice(worker->task, pool->attrs->nice);
-	kthread_bind_mask(worker->task, pool->attrs->cpumask);
 
 	/* start the newly created worker */
 	wake_up_process(worker->task);
@@ -2380,6 +2379,8 @@ static int worker_thread(void *__worker)
 	struct worker *worker = __worker;
 	struct worker_pool *pool = worker->pool;
 
+	current->flags |= PF_NO_SETAFFINITY;
+
 	/* attach the worker to the pool */
 	worker_attach_to_pool(worker, pool);
 
@@ -2494,6 +2495,7 @@ static int rescuer_thread(void *__rescuer)
 	struct list_head *scheduled = &rescuer->scheduled;
 	bool should_stop;
 
+	current->flags |= PF_NO_SETAFFINITY;
 	set_user_nice(current, RESCUER_NICE_LEVEL);
 
 	/*
@@ -4279,7 +4281,6 @@ static int init_rescuer(struct workqueue_struct *wq)
 	}
 
 	wq->rescuer = rescuer;
-	kthread_bind_mask(rescuer->task, cpu_possible_mask);
 	wake_up_process(rescuer->task);
 
 	return 0;
-- 
2.19.1.6.gb485710b