Re: [PATCH repost] sched: export sched_set/getaffinity to modules

On Fri, Jul 02, 2010 at 11:06:37PM +0200, Oleg Nesterov wrote:

quoted

On 07/02, Peter Zijlstra wrote:

quoted

On Fri, 2010-07-02 at 11:01 -0700, Sridhar Samudrala wrote:

quoted

 Does  it (Tejun's kthread_clone() patch) also  inherit the
cgroup of the caller?

Of course, its a simple do_fork() which inherits everything just as you
would expect from a similar sys_clone()/sys_fork() call.

Yes. And I'm afraid it can inherit more than we want. IIUC, this is called
from ioctl(), right?

Then the new thread becomes the natural child of the caller, and it shares
->mm with the parent. And files, dup_fd() without CLONE_FS.

Signals. Say, if you send SIGKILL to this new thread, it can't sleep in
TASK_INTERRUPTIBLE or KILLABLE after that. And this SIGKILL can be sent
just because the parent gets SIGQUIT or abother coredumpable signal.
Or the new thread can recieve SIGSTOP via ^Z.

Perhaps this is OK, I do not know. Just to remind that kernel_thread()
is merely clone(CLONE_VM).

Oleg.

With some machinery to stop it later, yes.
Oleg, how does the below look to you?

Here I explicitly drop the fds so we don't share them.
CLONE_VM takes care of sharing the mm I think.
About signals - for the vhost-net use this is OK as we use
uninterruptible sleep anyway (like the new kthread_worker does).

This code seems to work fine for me so far - any comments?

---

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index aabc8a1..72c7b17 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h

@@ -9,6 +9,11 @@ struct task_struct *kthread_create(int (*threadfn)(void *data),
 				   const char namefmt[], ...)
 	__attribute__((format(printf, 3, 4)));

+struct task_struct *kthread_create_inherit(int (*threadfn)(void *data),
+					   void *data,
+					   const char namefmt[], ...)
+	__attribute__((format(printf, 3, 4)));
+
 /**
  * kthread_run - create and wake a thread.
  * @threadfn: the function to run until signal_pending(current).

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 83911c7..b81588c 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c

@@ -149,6 +149,38 @@ struct task_struct *kthread_create(int (*threadfn)(void *data),
 }
 EXPORT_SYMBOL(kthread_create);

+/* Same as kthread_create, but inherit attributes (cgroups, priority, CPU mask)
+ * from current. */
+struct task_struct *kthread_create_inherit(int (*threadfn)(void *data),
+					   void *data,
+					   const char namefmt[],
+					   ...)
+{
+	struct kthread_create_info create;
+
+	create.threadfn = threadfn;
+	create.data = data;
+	init_completion(&create.done);
+
+	create_kthread(&create);
+	wait_for_completion(&create.done);
+
+	if (!IS_ERR(create.result)) {
+		va_list args;
+
+		/* Don't share files with parent as drivers use release for
+		 * close on exit, etc. */
+		exit_files(create.result);
+
+		va_start(args, namefmt);
+		vsnprintf(create.result->comm, sizeof(create.result->comm),
+			  namefmt, args);
+		va_end(args);
+	}
+	return create.result;
+}
+EXPORT_SYMBOL(kthread_create_inherit);
+
 /**
  * kthread_bind - bind a just-created kthread to a cpu.
  * @p: thread created by kthread_create().