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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, "J. Bruce Fields" <bfields@redhat.com>,
        Sasha Levin <sashal@kernel.org>, Tejun Heo <tj@kernel.org>
Subject: [PATCH 5.7 070/112] kthread: save thread function
Date:   Tue,  7 Jul 2020 17:17:15 +0200
Message-Id: <20200707145804.332402326@linuxfoundation.org>
In-Reply-To: <20200707145800.925304888@linuxfoundation.org>
References: <20200707145800.925304888@linuxfoundation.org>
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From: J. Bruce Fields <bfields@redhat.com>

[ Upstream commit 52782c92ac85c4e393eb4a903a62e6c24afa633f ]

It's handy to keep the kthread_fn just as a unique cookie to identify
classes of kthreads.  E.g. if you can verify that a given task is
running your thread_fn, then you may know what sort of type kthread_data
points to.

We'll use this in nfsd to pass some information into the vfs.  Note it
will need kthread_data() exported too.

Original-patch-by: Tejun Heo <tj@kernel.org>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/linux/kthread.h |  1 +
 kernel/kthread.c        | 17 +++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 8bbcaad7ef0f4..c2a274b79c429 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -57,6 +57,7 @@ bool kthread_should_stop(void);
 bool kthread_should_park(void);
 bool __kthread_should_park(struct task_struct *k);
 bool kthread_freezable_should_stop(bool *was_frozen);
+void *kthread_func(struct task_struct *k);
 void *kthread_data(struct task_struct *k);
 void *kthread_probe_data(struct task_struct *k);
 int kthread_park(struct task_struct *k);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index bfbfa481be3a5..b84fc7eec0358 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -46,6 +46,7 @@ struct kthread_create_info
 struct kthread {
 	unsigned long flags;
 	unsigned int cpu;
+	int (*threadfn)(void *);
 	void *data;
 	struct completion parked;
 	struct completion exited;
@@ -152,6 +153,20 @@ bool kthread_freezable_should_stop(bool *was_frozen)
 }
 EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);
 
+/**
+ * kthread_func - return the function specified on kthread creation
+ * @task: kthread task in question
+ *
+ * Returns NULL if the task is not a kthread.
+ */
+void *kthread_func(struct task_struct *task)
+{
+	if (task->flags & PF_KTHREAD)
+		return to_kthread(task)->threadfn;
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(kthread_func);
+
 /**
  * kthread_data - return data value specified on kthread creation
  * @task: kthread task in question
@@ -164,6 +179,7 @@ void *kthread_data(struct task_struct *task)
 {
 	return to_kthread(task)->data;
 }
+EXPORT_SYMBOL_GPL(kthread_data);
 
 /**
  * kthread_probe_data - speculative version of kthread_data()
@@ -244,6 +260,7 @@ static int kthread(void *_create)
 		do_exit(-ENOMEM);
 	}
 
+	self->threadfn = threadfn;
 	self->data = data;
 	init_completion(&self->exited);
 	init_completion(&self->parked);
-- 
2.25.1