Re: [PATCH 0/4] allow multiple kthreadd's

J. Bruce Fields
2020-05-06T15:37:00Z

On Tue, May 05, 2020 at 05:25:27PM -0400, J. Bruce Fields wrote:
> On Tue, May 05, 2020 at 05:09:56PM -0400, Tejun Heo wrote:
> > It's not the end of the world but a bit hacky. I wonder whether something
> > like the following would work better for identifying worker type so that you
> > can do sth like
> >
> > if (kthread_fn(current) == nfsd)
> > return kthread_data(current);
> > else
> > return NULL;
>
> Yes, definitely more generic, looks good to me.

This is what I'm testing with.

If it's OK with you, could I add your Signed-off-by and take it through
the nfsd tree? I'll have some other patches that will depend on it.

--b.

commit 379bfe5257b6
Author: Tejun Heo <tj@kernel.org>
Date: Tue May 5 21:26:07 2020 -0400

kthread: save thread function

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.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 8bbcaad7ef0f..c00ee443833f 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_fn(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 bfbfa481be3a..b87c4a9ba91d 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_fn - return the function specified on kthread creation
+ * @task: kthread task in question
+ *
+ * Returns NULL if the task is not a kthread.
+ */
+void *kthread_fn(struct task_struct *task)
+{
+ if (task->flags & PF_KTHREAD)
+ return to_kthread(task)->threadfn;
+ return NULL;
+}
+EXPORT_SYMBOL_GPL(kthread_fn);
+
/**
* 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);