[PATCH tip/core/rcu 6/6] rcu/segcblist: Add debug checks for segment lengths

paulmck
2021-01-06T01:27:15Z

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