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rcu: Add READ_ONCE() to rcu_node ->gp_seq

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The rcu_node structure's ->gp_seq field is read locklessly, so this
commit adds the READ_ONCE() to several loads in order to avoid
destructive compiler optimizations.

This data race was reported by KCSAN.  Not appropriate for backporting
because this affects only tracing and warnings.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-01-03 14:53:31 -08:00
parent b0c18c8773
commit 0937d04573
1 changed files with 5 additions and 4 deletions
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9
kernel/rcu/tree.c
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@ -1126,8 +1126,9 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
unsigned long gp_seq_req, const char *s)
{
trace_rcu_future_grace_period(rcu_state.name, rnp->gp_seq, gp_seq_req,
rnp->level, rnp->grplo, rnp->grphi, s);
trace_rcu_future_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
gp_seq_req, rnp->level,
rnp->grplo, rnp->grphi, s);
}
/*
@ -1904,7 +1905,7 @@ static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
rnp_c = rnp;
rnp = rnp->parent;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
oldmask = rnp_c->qsmask;
oldmask = READ_ONCE(rnp_c->qsmask);
}
/*
@ -2052,7 +2053,7 @@ int rcutree_dying_cpu(unsigned int cpu)
return 0;
blkd = !!(rnp->qsmask & rdp->grpmask);
trace_rcu_grace_period(rcu_state.name, rnp->gp_seq,
trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
blkd ? TPS("cpuofl") : TPS("cpuofl-bgp"));
return 0;
}