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rcu: Add quiescent states and boost states to show_rcu_gp_kthreads() output

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This commit adds each rcu_node structure's ->qsmask and "bBEG" output
indicating whether: (1) There is a boost kthread, (2) A reader needs
to be (or is in the process of being) boosted, (3) A reader is blocking
an expedited grace period, and (4) A reader is blocking a normal grace
period.  This helps diagnose RCU priority boosting failures.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2021-04-06 16:31:42 -07:00
parent 3066820034
commit 396eba65f6
3 changed files with 11 additions and 3 deletions
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1
kernel/rcu/tree.h
View file

@ -115,6 +115,7 @@ struct rcu_node {
/* boosting for this rcu_node structure. */
unsigned int boost_kthread_status;
/* State of boost_kthread_task for tracing. */
unsigned long n_boosts; /* Number of boosts for this rcu_node structure. */
#ifdef CONFIG_RCU_NOCB_CPU
struct swait_queue_head nocb_gp_wq[2];
/* Place for rcu_nocb_kthread() to wait GP. */

1
kernel/rcu/tree_plugin.h
View file

@ -1098,6 +1098,7 @@ static int rcu_boost(struct rcu_node *rnp)
/* Lock only for side effect: boosts task t's priority. */
rt_mutex_lock(&rnp->boost_mtx);
rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
rnp->n_boosts++;
return READ_ONCE(rnp->exp_tasks) != NULL ||
READ_ONCE(rnp->boost_tasks) != NULL;

12
kernel/rcu/tree_stall.h
View file

@ -749,9 +749,15 @@ void show_rcu_gp_kthreads(void)
if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq),
READ_ONCE(rnp->gp_seq_needed)))
continue;
pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n",
rnp->grplo, rnp->grphi, (long)data_race(rnp->gp_seq),
(long)data_race(rnp->gp_seq_needed));
pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld ->qsmask %#lx %c%c%c%c ->n_boosts %ld\n",
rnp->grplo, rnp->grphi,
(long)data_race(rnp->gp_seq), (long)data_race(rnp->gp_seq_needed),
data_race(rnp->qsmask),
".b"[!!data_race(rnp->boost_kthread_task)],
".B"[!!data_race(rnp->boost_tasks)],
".E"[!!data_race(rnp->exp_tasks)],
".G"[!!data_race(rnp->gp_tasks)],
data_race(rnp->n_boosts));
if (!rcu_is_leaf_node(rnp))
continue;
for_each_leaf_node_possible_cpu(rnp, cpu) {