kthread/smpboot: do not park in kthread_create_on_cpu()

kthread_create_on_cpu() was added by the commit 2a1d446019f9a5983e
("kthread: Implement park/unpark facility").  It is currently used only
when enabling new CPU.  For this purpose, the newly created kthread has to
be parked.

The CPU binding is a bit tricky.  The kthread is parked when the CPU has
not been allowed yet.  And the CPU is bound when the kthread is unparked.

The function would be useful for more per-CPU kthreads, e.g.
bnx2fc_thread, fcoethread.  For this purpose, the newly created kthread
should stay in the uninterruptible state.

This patch moves the parking into smpboot.  It binds the thread already
when created.  Then the function might be used universally.  Also the
behavior is consistent with kthread_create() and kthread_create_on_node().

Link: http://lkml.kernel.org/r/1470754545-17632-4-git-send-email-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 20bdf2c8d0f5fe02ebd075b55ba370f9f77e50bf..33058a4eeff6eb4724427c5fd124bb01979a76f3 100644 (file)
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -390,10 +390,10 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
                                   cpu);
        if (IS_ERR(p))
                return p;
+       kthread_bind(p, cpu);
+       /* CPU hotplug need to bind once again when unparking the thread. */
        set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
        to_kthread(p)->cpu = cpu;
-       /* Park the thread to get it out of TASK_UNINTERRUPTIBLE state */
-       kthread_park(p);
        return p;
 }
 
@@ -407,6 +407,10 @@ static void __kthread_unpark(struct task_struct *k, struct kthread *kthread)
         * which might be about to be cleared.
         */
        if (test_and_clear_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
+               /*
+                * Newly created kthread was parked when the CPU was offline.
+                * The binding was lost and we need to set it again.
+                */
                if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
                        __kthread_bind(k, kthread->cpu, TASK_PARKED);
                wake_up_state(k, TASK_PARKED);

diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 13bc43d1fb227f8ee0c55a411460200a2ac3b067..4a5c6e73ecd41e7107a89b098f4eea9fefc647f1 100644 (file)
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -186,6 +186,11 @@ __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
                kfree(td);
                return PTR_ERR(tsk);
        }
+       /*
+        * Park the thread so that it could start right on the CPU
+        * when it is available.
+        */
+       kthread_park(tsk);
        get_task_struct(tsk);
        *per_cpu_ptr(ht->store, cpu) = tsk;
        if (ht->create) {