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srcu: Fix __call_srcu()/process_srcu() datarace

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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>
This commit is contained in:
Paul E. McKenney 2019-12-22 19:32:54 -08:00
parent bb6d3fb354
commit 7ff8b4502b
1 changed files with 2 additions and 2 deletions
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4
kernel/rcu/srcutree.c
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@ -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);
}