Commit a2b354b9 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Add READ_ONCE() to rcu_do_batch() access to rcu_resched_ns 



Given that sysfs can change the value of rcu_resched_ns at any time,
this commit adds a READ_ONCE() to the sole access to that variable.
While in the area, this commit also adds bounds checking, clamping the
value to at least a millisecond, but no longer than a second.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent b5374b2d

kernel/rcu/tree.c

+6 −2
Original line number Diff line number Diff line
@@ -2394,8 +2394,12 @@ static void rcu_do_batch(struct rcu_data *rdp) 
	div = READ_ONCE(rcu_divisor);

	div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div;

	bl = max(rdp->blimit, pending >> div);

	if (unlikely(bl > 100))

		tlimit = local_clock() + rcu_resched_ns;

	if (unlikely(bl > 100)) {

		long rrn = READ_ONCE(rcu_resched_ns);



		rrn = rrn < NSEC_PER_MSEC ? NSEC_PER_MSEC : rrn > NSEC_PER_SEC ? NSEC_PER_SEC : rrn;

		tlimit = local_clock() + rrn;

	}

	trace_rcu_batch_start(rcu_state.name,

			      rcu_segcblist_n_cbs(&rdp->cblist), bl);

	rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);