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Subject[PATCH tip/core/rcu 1/4] srcu: Fix __call_srcu()/process_srcu() datarace
Date
From: "Paul E. McKenney" <paulmck@kernel.org>

The srcu_node 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: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/srcutree.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 657e6a7..b1edac9 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -550,7 +550,7 @@ static void srcu_gp_end(struct srcu_struct *ssp)
snp->srcu_have_cbs[idx] = gpseq;
rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1);
if (ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, gpseq))
- snp->srcu_gp_seq_needed_exp = gpseq;
+ WRITE_ONCE(snp->srcu_gp_seq_needed_exp, gpseq);
mask = snp->srcu_data_have_cbs[idx];
snp->srcu_data_have_cbs[idx] = 0;
spin_unlock_irq_rcu_node(snp);
@@ -660,7 +660,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
if (snp == sdp->mynode)
snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
if (!do_norm && ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, s))
- snp->srcu_gp_seq_needed_exp = s;
+ WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s);
spin_unlock_irqrestore_rcu_node(snp, flags);
}

--
2.9.5
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