sched: Revert 498657a478c60be092208422fefa9c7b248729c2

498657a478c60be092208422fefa9c7b248729c2 incorrectly assumed
that preempt wasn't disabled around context_switch() and thus
was fixing imaginary problem.  It also broke KVM because it
depended on ->sched_in() to be called with irq enabled so that
it can do smp calls from there.

Revert the incorrect commit and add comment describing different
contexts under with the two callbacks are invoked.

Avi: spotted transposed in/out in the added comment.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Avi Kivity <avi@redhat.com>
Cc: peterz@infradead.org
Cc: efault@gmx.de
Cc: rusty@rustcorp.com.au
LKML-Reference: <1259726212-30259-2-git-send-email-tj@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 72b1a10a59b6c178bf192f9d06c3c6c38a33e0c4..2e681d9555bdfd5db5326a6d37aab860cd417152 100644 (file)
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -105,6 +105,11 @@ struct preempt_notifier;
  * @sched_out: we've just been preempted
  *    notifier: struct preempt_notifier for the task being preempted
  *    next: the task that's kicking us out
+ *
+ * Please note that sched_in and out are called under different
+ * contexts.  sched_out is called with rq lock held and irq disabled
+ * while sched_in is called without rq lock and irq enabled.  This
+ * difference is intentional and depended upon by its users.
  */
 struct preempt_ops {
        void (*sched_in)(struct preempt_notifier *notifier, int cpu);

diff --git a/kernel/sched.c b/kernel/sched.c
index b3d4e2be95aa2c875ca4c7779763267e16f6caaa..1031cae39c4c8ba0fee55582f045ffbb47583700 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2768,9 +2768,9 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev)
        prev_state = prev->state;
        finish_arch_switch(prev);
        perf_event_task_sched_in(current, cpu_of(rq));
-       fire_sched_in_preempt_notifiers(current);
        finish_lock_switch(rq, prev);
 
+       fire_sched_in_preempt_notifiers(current);
        if (mm)
                mmdrop(mm);
        if (unlikely(prev_state == TASK_DEAD)) {