Messages in this thread | | | Date | Wed, 18 Nov 2020 19:52:23 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v2] rcu/segcblist: Add debug checks for segment lengths |
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On Wed, Nov 18, 2020 at 12:13:35PM -0800, Paul E. McKenney wrote: > On Wed, Nov 18, 2020 at 11:15:41AM -0500, Joel Fernandes (Google) wrote: > > After rcu_do_batch(), add a check for whether the seglen counts went to > > zero if the list was indeed empty. > > > > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> > > Queued for testing and further review, thank you!
FYI, the second of the two checks triggered in all four one-hour runs of TREE01, all four one-hour runs of TREE04, and one of the four one-hour runs of TREE07. This one:
WARN_ON_ONCE(count != 0 && rcu_segcblist_n_segment_cbs(&rdp->cblist) == 0);
That is, there are callbacks in the list, but the sum of the segment counts is nevertheless zero. The ->nocb_lock is held.
Thoughts?
Thanx, Paul
> > --- > > v1->v2: Added more debug checks. > > > > kernel/rcu/rcu_segcblist.c | 12 ++++++++++++ > > kernel/rcu/rcu_segcblist.h | 3 +++ > > kernel/rcu/tree.c | 2 ++ > > 3 files changed, 17 insertions(+) > > > > diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c > > index 5059b6102afe..6e98bb3804f0 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 totalling 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 cd35c9faaf51..46a42d77f7e1 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 totalling 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 f5b61e10f1de..91e35b521e51 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -2553,6 +2553,8 @@ static void rcu_do_batch(struct rcu_data *rdp) > > WARN_ON_ONCE(count == 0 && !rcu_segcblist_empty(&rdp->cblist)); > > WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) && > > count != 0 && rcu_segcblist_empty(&rdp->cblist)); > > + WARN_ON_ONCE(count == 0 && rcu_segcblist_n_segment_cbs(&rdp->cblist) != 0); > > + WARN_ON_ONCE(count != 0 && rcu_segcblist_n_segment_cbs(&rdp->cblist) == 0); > > > > rcu_nocb_unlock_irqrestore(rdp, flags); > > > > -- > > 2.29.2.299.gdc1121823c-goog
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