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rcu: Add WRITE_ONCE() to rcu_state ->gp_req_activity 

The rcu_state structure's ->gp_req_activity field is read locklessly,
so this commit adds the WRITE_ONCE() to an update in order to provide
proper documentation and READ_ONCE()/WRITE_ONCE() pairing.

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

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-01-03 15:17:12 -08:00
parent 0937d04573
commit 2906d2154c
1 changed files with 2 additions and 2 deletions
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4
kernel/rcu/tree.c
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@ -1200,7 +1200,7 @@ static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
}
trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
rcu_state.gp_req_activity = jiffies;
WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
if (!rcu_state.gp_kthread) {
trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
goto unlock_out;
@ -1775,7 +1775,7 @@ static void rcu_gp_cleanup(void)
rcu_segcblist_is_offloaded(&rdp->cblist);
if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
rcu_state.gp_req_activity = jiffies;
WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
trace_rcu_grace_period(rcu_state.name,
READ_ONCE(rcu_state.gp_seq),
TPS("newreq"));