Commit c5bacd94 authored Jul 20, 2018 by Paul E. McKenney

rcu: Motivate Tiny RCU forward progress



If a long-running CPU-bound in-kernel task invokes call_rcu(), the
callback won't be invoked until the next context switch.  If there are
no other runnable tasks (which is not an uncommon situation on deep
embedded systems), the callback might never be invoked.

This commit therefore causes rcu_check_callbacks() to ask the scheduler
for a context switch if there are callbacks posted that are still waiting
for a grace period.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent c116dba6

kernel/rcu/tiny.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -78,8 +78,12 @@ void rcu_qs(void)
		*/
		void rcu_check_callbacks(int user)
		{
		if (user)
		if (user) {
		rcu_qs();
		} else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
		set_tsk_need_resched(current);
		set_preempt_need_resched();
		}
		}

		/* Invoke the RCU callbacks whose grace period has elapsed. */

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