Merge tag 'core-rcu-2020-06-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU updates from Ingo Molnar:
 "The RCU updates for this cycle were:

   - RCU-tasks update, including addition of RCU Tasks Trace for BPF use
     and TASKS_RUDE_RCU

   - kfree_rcu() updates.

   - Remove scheduler locking restriction

   - RCU CPU stall warning updates.

   - Torture-test updates.

   - Miscellaneous fixes and other updates"

* tag 'core-rcu-2020-06-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (103 commits)
  rcu: Allow for smp_call_function() running callbacks from idle
  rcu: Provide rcu_irq_exit_check_preempt()
  rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter()
  rcu: Provide __rcu_is_watching()
  rcu: Provide rcu_irq_exit_preempt()
  rcu: Make RCU IRQ enter/exit functions rely on in_nmi()
  rcu/tree: Mark the idle relevant functions noinstr
  x86: Replace ist_enter() with nmi_enter()
  x86/mce: Send #MC singal from task work
  x86/entry: Get rid of ist_begin/end_non_atomic()
  sched,rcu,tracing: Avoid tracing before in_nmi() is correct
  sh/ftrace: Move arch_ftrace_nmi_{enter,exit} into nmi exception
  lockdep: Always inline lockdep_{off,on}()
  hardirq/nmi: Allow nested nmi_enter()
  arm64: Prepare arch_nmi_enter() for recursion
  printk: Disallow instrumenting print_nmi_enter()
  printk: Prepare for nested printk_nmi_enter()
  rcutorture: Convert ULONG_CMP_LT() to time_before()
  torture: Add a --kasan argument
  torture: Save a few lines by using config_override_param initially
  ...

1 files changed, 48 insertions, 0 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9a2fbf98fd6f..a05b85b3e0f7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2561,6 +2561,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 	 *
 	 * Pairs with the LOCK+smp_mb__after_spinlock() on rq->lock in
 	 * __schedule().  See the comment for smp_mb__after_spinlock().
+	 *
+	 * A similar smb_rmb() lives in try_invoke_on_locked_down_task().
 	 */
 	smp_rmb();
 	if (p->on_rq && ttwu_remote(p, wake_flags))
@@ -2635,6 +2637,52 @@ out:
 }
 
 /**
+ * try_invoke_on_locked_down_task - Invoke a function on task in fixed state
+ * @p: Process for which the function is to be invoked.
+ * @func: Function to invoke.
+ * @arg: Argument to function.
+ *
+ * If the specified task can be quickly locked into a definite state
+ * (either sleeping or on a given runqueue), arrange to keep it in that
+ * state while invoking @func(@arg).  This function can use ->on_rq and
+ * task_curr() to work out what the state is, if required.  Given that
+ * @func can be invoked with a runqueue lock held, it had better be quite
+ * lightweight.
+ *
+ * Returns:
+ *	@false if the task slipped out from under the locks.
+ *	@true if the task was locked onto a runqueue or is sleeping.
+ *		However, @func can override this by returning @false.
+ */
+bool try_invoke_on_locked_down_task(struct task_struct *p, bool (*func)(struct task_struct *t, void *arg), void *arg)
+{
+	bool ret = false;
+	struct rq_flags rf;
+	struct rq *rq;
+
+	lockdep_assert_irqs_enabled();
+	raw_spin_lock_irq(&p->pi_lock);
+	if (p->on_rq) {
+		rq = __task_rq_lock(p, &rf);
+		if (task_rq(p) == rq)
+			ret = func(p, arg);
+		rq_unlock(rq, &rf);
+	} else {
+		switch (p->state) {
+		case TASK_RUNNING:
+		case TASK_WAKING:
+			break;
+		default:
+			smp_rmb(); // See smp_rmb() comment in try_to_wake_up().
+			if (!p->on_rq)
+				ret = func(p, arg);
+		}
+	}
+	raw_spin_unlock_irq(&p->pi_lock);
+	return ret;
+}
+
+/**
  * wake_up_process - Wake up a specific process
  * @p: The process to be woken up.
  *