rcu: Make nocb_gp_wait() double-check unexpected-callback warning (3d05031a) · Commits · 戴 / test

Currently, nocb_gp_wait() unconditionally complains if there is a callback not already associated with a grace period. This assumes that either there was no such callback initially on the one hand, or that the rcu_advance_cbs() function assigned all such callbacks to a grace period on the other. However, in theory there are some situations that would prevent rcu_advance_cbs() from assigning all of the callbacks. This commit therefore checks for unassociated callbacks immediately after rcu_advance_cbs() returns, while the corresponding rcu_node structure's ->lock is still held. If there are unassociated callbacks at that point, the subsequent WARN_ON_ONCE() is disabled. Signed-off-by:

Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/tree_plugin.h

+5 −1

Original line number	Diff line number	Diff line
		@@ -1931,6 +1931,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
		struct rcu_data *rdp;
		struct rcu_node *rnp;
		unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning.
		bool wasempty = false;

		/*
		* Each pass through the following loop checks for CBs and for the
		@@ -1970,10 +1971,13 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
		rcu_seq_done(&rnp->gp_seq, cur_gp_seq))) {
		raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
		needwake_gp = rcu_advance_cbs(rnp, rdp);
		wasempty = rcu_segcblist_restempty(&rdp->cblist,
		RCU_NEXT_READY_TAIL);
		raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */
		}
		// Need to wait on some grace period?
		WARN_ON_ONCE(!rcu_segcblist_restempty(&rdp->cblist,
		WARN_ON_ONCE(wasempty &&
		!rcu_segcblist_restempty(&rdp->cblist,
		RCU_NEXT_READY_TAIL));
		if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq)) {
		if (!needwait_gp \|\|

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