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rcu: Tighten rcu_advance_cbs_nowake() checks

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commit 614ddad17f upstream.

Currently, rcu_advance_cbs_nowake() checks that a grace period is in
progress, however, that grace period could end just after the check.
This commit rechecks that a grace period is still in progress while
holding the rcu_node structure's lock.  The grace period cannot end while
the current CPU's rcu_node structure's ->lock is held, thus avoiding
false positives from the WARN_ON_ONCE().

As Daniel Vacek noted, it is not necessary for the rcu_node structure
to have a CPU that has not yet passed through its quiescent state.

Tested-by: Guillaume Morin <guillaume@morinfr.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Paul E. McKenney 2021-09-17 15:04:48 -07:00 committed by Greg Kroah-Hartman
parent 1b5553c79d
commit 75ca9c1d96
1 changed files with 4 additions and 3 deletions
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7
kernel/rcu/tree.c
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@ -1358,10 +1358,11 @@ static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp,
struct rcu_data *rdp)
{
rcu_lockdep_assert_cblist_protected(rdp);
if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) ||
!raw_spin_trylock_rcu_node(rnp))
if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) || !raw_spin_trylock_rcu_node(rnp))
return;
WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));
// The grace period cannot end while we hold the rcu_node lock.
if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))
WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));
raw_spin_unlock_rcu_node(rnp);
}