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srcu: Fix __call_srcu()/srcu_get_delay() datarace 

The srcu_struct 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 19:36:33 -08:00
parent 7ff8b4502b
commit 8c9e0cb323
1 changed files with 3 additions and 3 deletions
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6
kernel/rcu/srcutree.c
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@ -534,7 +534,7 @@ static void srcu_gp_end(struct srcu_struct *ssp)
rcu_seq_end(&ssp->srcu_gp_seq);
gpseq = rcu_seq_current(&ssp->srcu_gp_seq);
if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, gpseq))
ssp->srcu_gp_seq_needed_exp = gpseq;
WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, gpseq);
spin_unlock_irq_rcu_node(ssp);
mutex_unlock(&ssp->srcu_gp_mutex);
/* A new grace period can start at this point. But only one. */
@ -614,7 +614,7 @@ static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp
}
spin_lock_irqsave_rcu_node(ssp, flags);
if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s))
ssp->srcu_gp_seq_needed_exp = s;
WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s);
spin_unlock_irqrestore_rcu_node(ssp, flags);
}
@ -674,7 +674,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
smp_store_release(&ssp->srcu_gp_seq_needed, s); /*^^^*/
}
if (!do_norm && ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s))
ssp->srcu_gp_seq_needed_exp = s;
WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s);
/* If grace period not already done and none in progress, start it. */
if (!rcu_seq_done(&ssp->srcu_gp_seq, s) &&