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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>
This commit is contained in:
Paul E. McKenney 2020-01-03 11:42:05 -08:00
parent 39f91504a0
commit 710426068d
1 changed files with 3 additions and 1 deletions
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4
kernel/rcu/srcutree.c
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@ -450,7 +450,7 @@ static void srcu_gp_start(struct srcu_struct *ssp)
spin_unlock_rcu_node(sdp); /* Interrupts remain disabled. */ spin_unlock_rcu_node(sdp); /* Interrupts remain disabled. */
smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */ smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */
rcu_seq_start(&ssp->srcu_gp_seq); 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); 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. */ return; /* readers present, retry later. */
} }
srcu_flip(ssp); srcu_flip(ssp);
spin_lock_irq_rcu_node(ssp);
rcu_seq_set_state(&ssp->srcu_gp_seq, SRCU_STATE_SCAN2); 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) { if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {