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

Michael S. Tsirkin
2010-07-26T17:18:25Z

On Fri, Jul 02, 2010 at 11:06:37PM +0200, Oleg Nesterov wrote:
> On 07/02, Peter Zijlstra wrote:
> >
> > On Fri, 2010-07-02 at 11:01 -0700, Sridhar Samudrala wrote:
> > >
> > > 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().