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

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Date:   Tue, 5 May 2020 17:09:56 -0400
From:   Tejun Heo <tj@...nel.org>
To:     "J. Bruce Fields" <bfields@...ldses.org>
Cc:     "J. Bruce Fields" <bfields@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "open list:NFS, SUNRPC, AND..." <linux-nfs@...r.kernel.org>,
        Jeff Layton <jlayton@...hat.com>,
        David Howells <dhowells@...hat.com>, Shaohua Li <shli@...com>,
        Oleg Nesterov <oleg@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] allow multiple kthreadd's

Hello,

On Tue, May 05, 2020 at 05:01:18PM -0400, J. Bruce Fields wrote:
> On Mon, May 04, 2020 at 10:15:14PM -0400, J. Bruce Fields wrote:
> > Though now I'm feeling greedy: it would be nice to have both some kind
> > of global flag, *and* keep kthread->data pointing to svc_rqst (as that
> > would give me a simpler and quicker way to figure out which client is
> > conflicting).  Could I take a flag bit in kthread->flags, maybe?
> 
> Would something like this be too hacky?:

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;     

Thanks.

diff --git a/kernel/kthread.c b/kernel/kthread.c
index bfbfa481be3a..4f3ab9f2c994 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 +153,13 @@ bool kthread_freezable_should_stop(bool *was_frozen)
 }
 EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);
 
+void *kthread_fn(struct task_struct *task)
+{
+	if (task->flags & PF_KTHREAD)
+		return to_kthread(task)->threadfn;
+	return NULL;
+}
+
 /**
  * kthread_data - return data value specified on kthread creation
  * @task: kthread task in question
@@ -244,6 +252,7 @@ static int kthread(void *_create)
 		do_exit(-ENOMEM);
 	}
 
+	self->threadfn = threadfn;
 	self->data = data;
 	init_completion(&self->exited);
 	init_completion(&self->parked);

-- 
tejun