rcu: Add READ_ONCE() to rcu_do_batch() access to rcu_divisor (b5374b2d) · Commits · 戴 / test

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:

Paul E. McKenney <paulmck@kernel.org>

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,

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