srcu: Hold srcu_struct ->lock when updating ->srcu_gp_seq (71042606) · Commits · 戴 / test

A read of the srcu_struct structure's ->srcu_gp_seq field should not need READ_ONCE() when that structure's ->lock is held. Except that this lock is not always held when updating this field. This commit therefore acquires the lock around updates and removes a now-unneeded READ_ONCE(). This data race was reported by KCSAN. Signed-off-by:

Paul E. McKenney <paulmck@kernel.org> [ paulmck: Switch from READ_ONCE() to lock per Peter Zilstra question. ] Acked-by:

Peter Zijlstra (Intel) <peterz@infradead.org>

kernel/rcu/srcutree.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -450,7 +450,7 @@ static void srcu_gp_start(struct srcu_struct *ssp)
		spin_unlock_rcu_node(sdp); /* Interrupts remain disabled. */
		smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */
		rcu_seq_start(&ssp->srcu_gp_seq);
		state = rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq));
		state = rcu_seq_state(ssp->srcu_gp_seq);
		WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
		}

		@@ -1130,7 +1130,9 @@ static void srcu_advance_state(struct srcu_struct *ssp)
		return; /* readers present, retry later. */
		}
		srcu_flip(ssp);
		spin_lock_irq_rcu_node(ssp);
		rcu_seq_set_state(&ssp->srcu_gp_seq, SRCU_STATE_SCAN2);
		spin_unlock_irq_rcu_node(ssp);
		}

		if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {

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