[tip/core/rcu,28/30] rcu: Mark rcu_state.ncpus to detect concurrent writes
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Message ID 20200214235607.13749-28-paulmck@kernel.org
State In Next
Commit de7137a57c5c6a9244191c35a38eafc1a044a391
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Series
  • Miscellaneous fixes for v5.7
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Commit Message

Paul E. McKenney Feb. 14, 2020, 11:56 p.m. UTC 
From: "Paul E. McKenney" <paulmck@kernel.org>

The rcu_state structure's ncpus field is only to be modified by the
CPU-hotplug CPU-online code path, which is single-threaded.  This
commit therefore enlists KCSAN's help in enforcing this restriction.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree.c | 1 +
 1 file changed, 1 insertion(+)

Patch
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diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4146207..3a60a160 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3397,6 +3397,7 @@  void rcu_cpu_starting(unsigned int cpu)
 	nbits = bitmap_weight(&oldmask, BITS_PER_LONG);
 	/* Allow lockless access for expedited grace periods. */
 	smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + nbits); /* ^^^ */
+	ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus);
 	rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
 	rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
 	rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);