Commit b4e6039e authored by Joel Fernandes (Google)'s avatar Joel Fernandes (Google) Committed by Paul E. McKenney
Browse files

rcu/segcblist: Add debug checks for segment lengths 



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: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Fix queue/segment-length checks. ]
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 3afe7fa5

kernel/rcu/rcu_segcblist.c

+12 −0
Original line number Diff line number Diff line
@@ -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)

{

kernel/rcu/rcu_segcblist.h

+3 −0
Original line number Diff line number Diff line
@@ -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,

kernel/rcu/tree.c

+6 −2
Original line number Diff line number Diff line
@@ -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);