From a65d40961dc70d15dec046c2ee88c556f57940b2 Mon Sep 17 00:00:00 2001 From: Petr Mladek Date: Tue, 11 Oct 2016 13:55:23 -0700 Subject: [PATCH] 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 Reviewed-by: Thomas Gleixner Cc: Oleg Nesterov Cc: Tejun Heo Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Steven Rostedt Cc: "Paul E. McKenney" Cc: Josh Triplett Cc: Jiri Kosina Cc: Borislav Petkov Cc: Michal Hocko Cc: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/kthread.c | 8 ++++++-- kernel/smpboot.c | 5 +++++ 2 files changed, 11 insertions(+), 2 deletions(-) diff --git a/kernel/kthread.c b/kernel/kthread.c index c52a05a8ec52..f5dc0b151d61 100644 --- 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 13bc43d1fb22..4a5c6e73ecd4 100644 --- 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) {