rcu: Add READ_ONCE() to rcu_do_batch() access to rcu_resched_ns (a2b354b9) · Commits · 戴 / test

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:

Paul E. McKenney <paulmck@kernel.org>

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);

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