Commit b5374b2d authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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



Given that sysfs can change the value of rcu_divisor 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
a shift that makes sense for a signed long.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 2130c6b4

kernel/rcu/tree.c

+4 −1
Original line number Diff line number Diff line
@@ -2362,6 +2362,7 @@ int rcutree_dead_cpu(unsigned int cpu) 
 */

static void rcu_do_batch(struct rcu_data *rdp)

{

	int div;

	unsigned long flags;

	const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&

			       rcu_segcblist_is_offloaded(&rdp->cblist);
@@ -2390,7 +2391,9 @@ static void rcu_do_batch(struct rcu_data *rdp) 
	rcu_nocb_lock(rdp);

	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));

	pending = rcu_segcblist_n_cbs(&rdp->cblist);

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

	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;

	trace_rcu_batch_start(rcu_state.name,