Commit 8c9e0cb3 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

srcu: Fix __call_srcu()/srcu_get_delay() datarace 



The srcu_struct structure's ->srcu_gp_seq_needed_exp field is accessed
locklessly, so updates must use WRITE_ONCE().  This commit therefore
adds the needed WRITE_ONCE() invocations.

This data race was reported by KCSAN.  Not appropriate for backporting
due to failure being unlikely.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 7ff8b450

kernel/rcu/srcutree.c

+3 −3
Original line number Diff line number Diff line
@@ -534,7 +534,7 @@ static void srcu_gp_end(struct srcu_struct *ssp) 
	rcu_seq_end(&ssp->srcu_gp_seq);

	gpseq = rcu_seq_current(&ssp->srcu_gp_seq);

	if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, gpseq))

		ssp->srcu_gp_seq_needed_exp = gpseq;

		WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, gpseq);

	spin_unlock_irq_rcu_node(ssp);

	mutex_unlock(&ssp->srcu_gp_mutex);

	/* A new grace period can start at this point.  But only one. */
@@ -614,7 +614,7 @@ static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp 
	}

	spin_lock_irqsave_rcu_node(ssp, flags);

	if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s))

		ssp->srcu_gp_seq_needed_exp = s;

		WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s);

	spin_unlock_irqrestore_rcu_node(ssp, flags);

}
@@ -674,7 +674,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp, 
		smp_store_release(&ssp->srcu_gp_seq_needed, s); /*^^^*/

	}

	if (!do_norm && ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s))

		ssp->srcu_gp_seq_needed_exp = s;

		WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s);



	/* If grace period not already done and none in progress, start it. */

	if (!rcu_seq_done(&ssp->srcu_gp_seq, s) &&

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