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From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
	mingo@kernel.org, jiangshanlai@gmail.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
	"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 6/6] rcu/segcblist: Add debug checks for segment lengths
Date: Tue,  5 Jan 2021 17:26:17 -0800
Message-ID: <20210106012617.14122-6-paulmck@kernel.org> (raw)
In-Reply-To: <20210106012541.GA13972@paulmck-ThinkPad-P72>

From: "Joel Fernandes (Google)" <joel@joelfernandes.org>

This commit adds debug checks near the end of rcu_do_batch() that emit
warnings if an empty rcu_segcblist structure has non-zero segment counts,
or, conversely, if a non-empty structure has all-zero segment counts.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Fix queue/segment-length checks. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/rcu_segcblist.c | 12 ++++++++++++
 kernel/rcu/rcu_segcblist.h |  3 +++
 kernel/rcu/tree.c          |  8 ++++++--
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
index 5059b61..094de25 100644
--- a/kernel/rcu/rcu_segcblist.c
+++ b/kernel/rcu/rcu_segcblist.c
@@ -94,6 +94,18 @@ static long rcu_segcblist_get_seglen(struct rcu_segcblist *rsclp, int seg)
 	return READ_ONCE(rsclp->seglen[seg]);
 }
 
+/* Return number of callbacks in segmented callback list by summing seglen. */
+long rcu_segcblist_n_segment_cbs(struct rcu_segcblist *rsclp)
+{
+	long len = 0;
+	int i;
+
+	for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++)
+		len += rcu_segcblist_get_seglen(rsclp, i);
+
+	return len;
+}
+
 /* Set the length of a segment of the rcu_segcblist structure. */
 static void rcu_segcblist_set_seglen(struct rcu_segcblist *rsclp, int seg, long v)
 {
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index cd35c9f..18e101d 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -15,6 +15,9 @@ static inline long rcu_cblist_n_cbs(struct rcu_cblist *rclp)
 	return READ_ONCE(rclp->len);
 }
 
+/* Return number of callbacks in segmented callback list by summing seglen. */
+long rcu_segcblist_n_segment_cbs(struct rcu_segcblist *rsclp);
+
 void rcu_cblist_init(struct rcu_cblist *rclp);
 void rcu_cblist_enqueue(struct rcu_cblist *rclp, struct rcu_head *rhp);
 void rcu_cblist_flush_enqueue(struct rcu_cblist *drclp,
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 6bf269c..8086c04 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2434,6 +2434,7 @@ int rcutree_dead_cpu(unsigned int cpu)
 static void rcu_do_batch(struct rcu_data *rdp)
 {
 	int div;
+	bool __maybe_unused empty;
 	unsigned long flags;
 	const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist);
 	struct rcu_head *rhp;
@@ -2548,9 +2549,12 @@ static void rcu_do_batch(struct rcu_data *rdp)
 	 * The following usually indicates a double call_rcu().  To track
 	 * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.
 	 */
-	WARN_ON_ONCE(count == 0 && !rcu_segcblist_empty(&rdp->cblist));
+	empty = rcu_segcblist_empty(&rdp->cblist);
+	WARN_ON_ONCE(count == 0 && !empty);
 	WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
-		     count != 0 && rcu_segcblist_empty(&rdp->cblist));
+		     count != 0 && empty);
+	WARN_ON_ONCE(count == 0 && rcu_segcblist_n_segment_cbs(&rdp->cblist) != 0);
+	WARN_ON_ONCE(!empty && rcu_segcblist_n_segment_cbs(&rdp->cblist) == 0);
 
 	rcu_nocb_unlock_irqrestore(rdp, flags);
 
-- 
2.9.5


      parent reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-06  1:25 [PATCH tip/core/rcu 0/6] Track callbacks on a per-segment basis Paul E. McKenney
2021-01-06  1:26 ` [PATCH tip/core/rcu 1/6] rcu/tree: Make rcu_do_batch count how many callbacks were executed paulmck
2021-01-06  1:26 ` [PATCH tip/core/rcu 2/6] rcu/segcblist: Add additional comments to explain smp_mb() paulmck
2021-01-06  1:26 ` [PATCH tip/core/rcu 3/6] rcu/segcblist: Add counters to segcblist datastructure paulmck
2021-01-06  1:26 ` [PATCH tip/core/rcu 4/6] rcu/tree: segcblist: Remove redundant smp_mb()s paulmck
2021-01-06  1:26 ` [PATCH tip/core/rcu 5/6] rcu/trace: Add tracing for how segcb list changes paulmck
2021-01-06  1:26 ` paulmck [this message]

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