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rcu/segcblist: Add debug checks for segment lengths

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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>
This commit is contained in:
Joel Fernandes (Google) 2020-11-18 11:15:41 -05:00 committed by Paul E. McKenney
parent 3afe7fa535
commit b4e6039e8a
3 changed files with 21 additions and 2 deletions
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12
kernel/rcu/rcu_segcblist.c
View File

@ -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)
{

3
kernel/rcu/rcu_segcblist.h
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@ -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,

8
kernel/rcu/tree.c
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@ -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);