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Message-Id: <20180625230427.13877-1-paulmck@linux.vnet.ibm.com>
Date: Mon, 25 Jun 2018 16:04:23 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 1/5] rcu: Add debugging info to assertion
The WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp()) in
rcu_gp_cleanup() triggers (inexplicably, of course) every so often.
This commit therefore extracts more information.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
kernel/rcu/tree.c | 5 ++++-
kernel/rcu/tree.h | 2 ++
kernel/rcu/tree_plugin.h | 38 ++++++++++++++++++++++++++++++++++++--
3 files changed, 42 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index aa7cade1b9f3..79c7fe978b17 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2084,7 +2084,8 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
*/
rcu_for_each_node_breadth_first(rsp, rnp) {
raw_spin_lock_irq_rcu_node(rnp);
- WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
+ if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
+ dump_blkd_tasks(rnp, 10);
WARN_ON_ONCE(rnp->qsmask);
WRITE_ONCE(rnp->completed, rsp->gpnum);
rdp = this_cpu_ptr(rsp->rda);
@@ -2294,6 +2295,7 @@ rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
+ rnp->completedqs = rnp->gpnum;
mask = rnp->grpmask;
if (rnp->parent == NULL) {
@@ -3930,6 +3932,7 @@ static void __init rcu_init_one(struct rcu_state *rsp)
&rcu_fqs_class[i], fqs[i]);
rnp->gpnum = rsp->gpnum;
rnp->completed = rsp->completed;
+ rnp->completedqs = rsp->completed;
rnp->qsmask = 0;
rnp->qsmaskinit = 0;
rnp->grplo = j * cpustride;
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 78e051dffc5b..7365ac53fdd9 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -87,6 +87,7 @@ struct rcu_node {
unsigned long completed; /* Last GP completed for this node. */
/* This will either be equal to or one */
/* behind the root rcu_node's gpnum. */
+ unsigned long completedqs; /* All QSes done for this node. */
unsigned long qsmask; /* CPUs or groups that need to switch in */
/* order for current grace period to proceed.*/
/* In leaf rcu_node, each bit corresponds to */
@@ -453,6 +454,7 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
static void rcu_preempt_check_callbacks(void);
void call_rcu(struct rcu_head *head, rcu_callback_t func);
static void __init __rcu_init_preempt(void);
+static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck);
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
static void invoke_rcu_callbacks_kthread(void);
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 7fd12039e512..17b67ecf7dff 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -260,8 +260,10 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
* ->exp_tasks pointers, respectively, to reference the newly
* blocked tasks.
*/
- if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD))
+ if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) {
rnp->gp_tasks = &t->rcu_node_entry;
+ WARN_ON_ONCE(rnp->completedqs == rnp->gpnum);
+ }
if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
rnp->exp_tasks = &t->rcu_node_entry;
WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
@@ -535,6 +537,8 @@ void rcu_read_unlock_special(struct task_struct *t)
WARN_ON_ONCE(rnp != t->rcu_blocked_node);
WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
+ WARN_ON_ONCE(rnp->completedqs == rnp->gpnum &&
+ (!empty_norm || rnp->qsmask));
empty_exp = sync_rcu_preempt_exp_done(rnp);
smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
np = rcu_next_node_entry(t, rnp);
@@ -697,7 +701,8 @@ 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");
- WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
+ if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
+ dump_blkd_tasks(rnp, 10);
if (rcu_preempt_has_tasks(rnp)) {
rnp->gp_tasks = rnp->blkd_tasks.next;
t = container_of(rnp->gp_tasks, struct task_struct,
@@ -841,6 +846,27 @@ void exit_rcu(void)
__rcu_read_unlock();
}
+/*
+ * Dump the blocked-tasks state, but limit the list dump to the
+ * specified number of elements.
+ */
+static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
+{
+ int i;
+ struct list_head *lhp;
+
+ lockdep_assert_held(&rnp->lock);
+ pr_info("%s: grp: %d-%d level: %d ->qamask %#lx ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p &->blkd_tasks: %p offset: %u\n", __func__, rnp->grplo, rnp->grphi, rnp->level, rnp->qsmask, rnp->gp_tasks, rnp->boost_tasks, rnp->exp_tasks, &rnp->blkd_tasks, (unsigned int)offsetof(typeof(*rnp), blkd_tasks));
+ pr_cont("\t->blkd_tasks");
+ i = 0;
+ list_for_each(lhp, &rnp->blkd_tasks) {
+ pr_cont(" %p", lhp);
+ if (++i >= 10)
+ break;
+ }
+ pr_cont("\n");
+}
+
#else /* #ifdef CONFIG_PREEMPT_RCU */
static struct rcu_state *const rcu_state_p = &rcu_sched_state;
@@ -949,6 +975,14 @@ void exit_rcu(void)
{
}
+/*
+ * Dump the guaranteed-empty blocked-tasks state. Trust but verify.
+ */
+static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
+{
+ WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
+}
+
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
#ifdef CONFIG_RCU_BOOST
--
2.17.1
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