[PATCH tip/core/rcu 03/11] rcu: Use lockdep rather than comment to enforce lock held

From: paulmck
Date: Mon Dec 09 2019 - 23:26:53 EST

From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>

The rcu_preempt_check_blocked_tasks() function has a comment
that states that the rcu_node structure's ->lock must be held,
which might be informative, but which carries little weight if
not read. This commit therefore removes this comment in favor of
raw_lockdep_assert_held_rcu_node(), which will complain quite
visibly if the required lock is not held.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
kernel/rcu/tree_plugin.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index fe5f448..ed54d36 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -648,8 +648,7 @@ static void rcu_read_unlock_special(struct task_struct *t)
* Check that the list of blocked tasks for the newly completed grace
* period is in fact empty. It is a serious bug to complete a grace
* period that still has RCU readers blocked! This function must be
- * invoked -before- updating this rnp's ->gp_seq, and the rnp's ->lock
- * must be held by the caller.
+ * invoked -before- updating this rnp's ->gp_seq.
* Also, if there are blocked tasks on the list, they automatically
* block the newly created grace period, so set up ->gp_tasks accordingly.
@@ -659,6 +658,7 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
struct task_struct *t;

RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
+ raw_lockdep_assert_held_rcu_node(rnp);
if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
dump_blkd_tasks(rnp, 10);
if (rcu_preempt_has_tasks(rnp) &&