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Date: Tue, 5 Jan 2021 20:48:50 -0800
From: paulmck@...nel.org
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
jiangshanlai@...il.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@...nel.org>
Subject: [PATCH tip/core/rcu 18/21] rcu/nocb: Add grace period and task state to show_rcu_nocb_state() output
From: "Paul E. McKenney" <paulmck@...nel.org>
This commit improves debuggability by indicating which grace period each
batch of nocb callbacks is waiting on and by showing the task state and
last CPU for reach nocb kthread.
[ paulmck: Handle !SMP CB offloading per kernel test robot feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
kernel/rcu/rcu_segcblist.h | 11 +++++++++++
kernel/rcu/tree_plugin.h | 39 ++++++++++++++++++++++++++++++++-------
2 files changed, 43 insertions(+), 7 deletions(-)
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index afad6fc..3110602 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -117,6 +117,17 @@ static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
return !READ_ONCE(*READ_ONCE(rsclp->tails[seg]));
}
+/*
+ * Is the specified segment of the specified rcu_segcblist structure
+ * empty of callbacks?
+ */
+static inline bool rcu_segcblist_segempty(struct rcu_segcblist *rsclp, int seg)
+{
+ if (seg == RCU_DONE_TAIL)
+ return &rsclp->head == rsclp->tails[RCU_DONE_TAIL];
+ return rsclp->tails[seg - 1] == rsclp->tails[seg];
+}
+
void rcu_segcblist_inc_len(struct rcu_segcblist *rsclp);
void rcu_segcblist_add_len(struct rcu_segcblist *rsclp, long v);
void rcu_segcblist_init(struct rcu_segcblist *rsclp);
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 8641b72..5ee1113 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2672,6 +2672,19 @@ void rcu_bind_current_to_nocb(void)
}
EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);
+// The ->on_cpu field is available only in CONFIG_SMP=y, so...
+#ifdef CONFIG_SMP
+static char *show_rcu_should_be_on_cpu(struct task_struct *tsp)
+{
+ return tsp && tsp->state == TASK_RUNNING && !tsp->on_cpu ? "!" : "";
+}
+#else // #ifdef CONFIG_SMP
+static char *show_rcu_should_be_on_cpu(struct task_struct *tsp)
+{
+ return "";
+}
+#endif // #else #ifdef CONFIG_SMP
+
/*
* Dump out nocb grace-period kthread state for the specified rcu_data
* structure.
@@ -2680,7 +2693,7 @@ static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
{
struct rcu_node *rnp = rdp->mynode;
- pr_info("nocb GP %d %c%c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu\n",
+ pr_info("nocb GP %d %c%c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu %c CPU %d%s\n",
rdp->cpu,
"kK"[!!rdp->nocb_gp_kthread],
"lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)],
@@ -2694,12 +2707,17 @@ static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
".B"[!!rdp->nocb_gp_bypass],
".G"[!!rdp->nocb_gp_gp],
(long)rdp->nocb_gp_seq,
- rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops));
+ rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops),
+ rdp->nocb_gp_kthread ? task_state_to_char(rdp->nocb_gp_kthread) : '.',
+ rdp->nocb_cb_kthread ? (int)task_cpu(rdp->nocb_gp_kthread) : -1,
+ show_rcu_should_be_on_cpu(rdp->nocb_cb_kthread));
}
/* Dump out nocb kthread state for the specified rcu_data structure. */
static void show_rcu_nocb_state(struct rcu_data *rdp)
{
+ char bufw[20];
+ char bufr[20];
struct rcu_segcblist *rsclp = &rdp->cblist;
bool waslocked;
bool wastimer;
@@ -2708,7 +2726,9 @@ static void show_rcu_nocb_state(struct rcu_data *rdp)
if (rdp->nocb_gp_rdp == rdp)
show_rcu_nocb_gp_state(rdp);
- pr_info(" CB %d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%c%c%c q%ld\n",
+ sprintf(bufw, "%ld", rsclp->gp_seq[RCU_WAIT_TAIL]);
+ sprintf(bufr, "%ld", rsclp->gp_seq[RCU_NEXT_READY_TAIL]);
+ pr_info(" CB %d^%d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%s%c%s%c%c q%ld %c CPU %d%s\n",
rdp->cpu, rdp->nocb_gp_rdp->cpu,
"kK"[!!rdp->nocb_cb_kthread],
"bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)],
@@ -2720,11 +2740,16 @@ static void show_rcu_nocb_state(struct rcu_data *rdp)
jiffies - rdp->nocb_nobypass_last,
rdp->nocb_nobypass_count,
".D"[rcu_segcblist_ready_cbs(rsclp)],
- ".W"[!rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)],
- ".R"[!rcu_segcblist_restempty(rsclp, RCU_WAIT_TAIL)],
- ".N"[!rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL)],
+ ".W"[!rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL)],
+ rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL) ? "" : bufw,
+ ".R"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL)],
+ rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL) ? "" : bufr,
+ ".N"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_TAIL)],
".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
- rcu_segcblist_n_cbs(&rdp->cblist));
+ rcu_segcblist_n_cbs(&rdp->cblist),
+ rdp->nocb_cb_kthread ? task_state_to_char(rdp->nocb_cb_kthread) : '.',
+ rdp->nocb_cb_kthread ? (int)task_cpu(rdp->nocb_gp_kthread) : -1,
+ show_rcu_should_be_on_cpu(rdp->nocb_cb_kthread));
/* It is OK for GP kthreads to have GP state. */
if (rdp->nocb_gp_rdp == rdp)
--
2.9.5
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