perf: Cure task_oncpu_function_call() races

Oleg reported that on architectures with
__ARCH_WANT_INTERRUPTS_ON_CTXSW the IPI from
task_oncpu_function_call() can land before perf_event_task_sched_in()
and cause interesting situations for eg. perf_install_in_context().

This patch reworks the task_oncpu_function_call() interface to give a
more usable primitive as well as rework all its users to hopefully be
more obvious as well as remove the races.

While looking at the code I also found a number of races against
perf_event_task_sched_out() which can flip contexts between tasks so
plug those too.

Reported-and-reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 4 insertions, 25 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 18d38e4ec7ba..31cb5d5e1aac 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2265,27 +2265,6 @@ void kick_process(struct task_struct *p)
 EXPORT_SYMBOL_GPL(kick_process);
 #endif /* CONFIG_SMP */
 
-/**
- * task_oncpu_function_call - call a function on the cpu on which a task runs
- * @p:          the task to evaluate
- * @func:       the function to be called
- * @info:       the function call argument
- *
- * Calls the function @func when the task is currently running. This might
- * be on the current CPU, which just calls the function directly
- */
-void task_oncpu_function_call(struct task_struct *p,
-                              void (*func) (void *info), void *info)
-{
-        int cpu;
-
-        preempt_disable();
-        cpu = task_cpu(p);
-        if (task_curr(p))
-                smp_call_function_single(cpu, func, info, 1);
-        preempt_enable();
-}
-
 #ifdef CONFIG_SMP
 /*
  * ->cpus_allowed is protected by either TASK_WAKING or rq->lock held.
@@ -2776,9 +2755,12 @@ static inline void
 prepare_task_switch(struct rq *rq, struct task_struct *prev,
                     struct task_struct *next)
 {
+        sched_info_switch(prev, next);
+        perf_event_task_sched_out(prev, next);
         fire_sched_out_preempt_notifiers(prev, next);
         prepare_lock_switch(rq, next);
         prepare_arch_switch(next);
+        trace_sched_switch(prev, next);
 }
 
 /**
@@ -2911,7 +2893,7 @@ context_switch(struct rq *rq, struct task_struct *prev,
         struct mm_struct *mm, *oldmm;
 
         prepare_task_switch(rq, prev, next);
-        trace_sched_switch(prev, next);
+
         mm = next->mm;
         oldmm = prev->active_mm;
         /*
@@ -3989,9 +3971,6 @@ need_resched_nonpreemptible:
         rq->skip_clock_update = 0;
 
         if (likely(prev != next)) {
-                sched_info_switch(prev, next);
-                perf_event_task_sched_out(prev, next);
-
                 rq->nr_switches++;
                 rq->curr = next;
                 ++*switch_count;