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    Subject[PATCH 1/1] kthread: disable preemption during complete()
    After a kthread is created it signals the requester using complete()
    and enters TASK_UNINTERRUPTIBLE. However, since complete() wakes up
    the requesting thread this can cause a preemption. The preemption will
    not remove the task from the runqueue (for that schedule() has to be
    invoked directly).

    This is a problem if directly after kthread creation you try to do a
    kthread_bind(), which will block in HZ steps until the thread is off
    the runqueue.

    This patch disables preemption during complete(), since we call
    schedule() directly afterwards, so it will correctly enter
    TASK_UNINTERRUPTIBLE. This speeds up kthread creation/binding during
    cpu hotplug significantly.

    Change-Id: I856ddd4e01ebdb198ba90f343b4a0c5933fd2b23
    Signed-off-by: Peter Boonstoppel <>
    kernel/kthread.c | 5 +++++
    1 files changed, 5 insertions(+), 0 deletions(-)

    diff --git a/kernel/kthread.c b/kernel/kthread.c
    index b579af5..f681b14 100644
    --- a/kernel/kthread.c
    +++ b/kernel/kthread.c
    @@ -16,6 +16,8 @@
    #include <linux/mutex.h>
    #include <linux/slab.h>
    #include <linux/freezer.h>
    +#include <linux/preempt.h>
    +#include <linux/thread_info.h>
    #include <trace/events/sched.h>

    static DEFINE_SPINLOCK(kthread_create_lock);
    @@ -113,7 +115,10 @@ static int kthread(void *_create)
    /* OK, tell user we're spawned, wait for stop or wakeup */
    create->result = current;
    + preempt_disable();
    + clear_need_resched();
    + preempt_enable_no_resched();

    ret = -EINTR;

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      Last update: 2012-07-25 03:01    [W:0.030 / U:9.128 seconds]
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