rcu: Optimize and protect atomic_cmpxchg() loop (faa059c3) · Commits · 戴 / test

This commit reworks the atomic_cmpxchg() loop in rcu_eqs_special_set() to do only the initial read from the current CPU's rcu_data structure's ->dynticks field explicitly. On subsequent passes, this value is instead retained from the failing atomic_cmpxchg() operation. Signed-off-by:

Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/tree.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -342,14 +342,17 @@ bool rcu_eqs_special_set(int cpu)
		{
		int old;
		int new;
		int new_old;
		struct rcu_data *rdp = &per_cpu(rcu_data, cpu);

		new_old = atomic_read(&rdp->dynticks);
		do {
		old = atomic_read(&rdp->dynticks);
		old = new_old;
		if (old & RCU_DYNTICK_CTRL_CTR)
		return false;
		new = old \| RCU_DYNTICK_CTRL_MASK;
		} while (atomic_cmpxchg(&rdp->dynticks, old, new) != old);
		new_old = atomic_cmpxchg(&rdp->dynticks, old, new);
		} while (new_old != old);
		return true;
		}

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