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authorPaul E. McKenney <paulmck@kernel.org>2020-01-03 11:42:05 -0800
committerPaul E. McKenney <paulmck@kernel.org>2020-02-20 16:01:11 -0800
commit710426068dc60f2d2e139478d6185710802cdc0a (patch)
tree00005fee34c298dea42e655f5e06a42392cba95d /kernel/rcu
parent39f91504a03a7a2abdb52205106942fa4a548d0d (diff)
downloadlinux-710426068dc60f2d2e139478d6185710802cdc0a.tar.bz2
srcu: Hold srcu_struct ->lock when updating ->srcu_gp_seq
A read of the srcu_struct structure's ->srcu_gp_seq field should not need READ_ONCE() when that structure's ->lock is held. Except that this lock is not always held when updating this field. This commit therefore acquires the lock around updates and removes a now-unneeded READ_ONCE(). This data race was reported by KCSAN. Signed-off-by: Paul E. McKenney <paulmck@kernel.org> [ paulmck: Switch from READ_ONCE() to lock per Peter Zilstra question. ] Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/srcutree.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 119a37319e67..c19c1df0d198 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -450,7 +450,7 @@ static void srcu_gp_start(struct srcu_struct *ssp)
spin_unlock_rcu_node(sdp); /* Interrupts remain disabled. */
smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */
rcu_seq_start(&ssp->srcu_gp_seq);
- state = rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq));
+ state = rcu_seq_state(ssp->srcu_gp_seq);
WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
}
@@ -1130,7 +1130,9 @@ static void srcu_advance_state(struct srcu_struct *ssp)
return; /* readers present, retry later. */
}
srcu_flip(ssp);
+ spin_lock_irq_rcu_node(ssp);
rcu_seq_set_state(&ssp->srcu_gp_seq, SRCU_STATE_SCAN2);
+ spin_unlock_irq_rcu_node(ssp);
}
if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {