On Mon, Oct 26, 2020 at 01:32:12AM +0100, Frederic Weisbecker wrote:
> On Wed, Oct 21, 2020 at 03:08:09PM -0400, Joel Fernandes (Google) wrote:
> > @@ -307,6 +317,7 @@ void rcu_segcblist_extract_done_cbs(struct
> > rcu_segcblist *rsclp,
> >
> > if (!rcu_segcblist_ready_cbs(rsclp))
> > return; /* Nothing to do. */
> > + rclp->len = rcu_segcblist_get_seglen(rsclp, RCU_DONE_TAIL);
>
> I realize, doesn't it break the unsegmented count in srcu_invoke_callbacks() ?
>
> It still does rcu_segcblist_insert_count(), so it adds zero to rsclp->len
> which thus doesn't get cleared and probably keeps growing.
You are right. This needs changing :-( Its my fault, I did not test SRCU
torture tests which are indeed failing.
I fixed it with the diff attached to the end of the email and will test it
more.
> > *rclp->tail = rsclp->head;
> > WRITE_ONCE(rsclp->head, *rsclp->tails[RCU_DONE_TAIL]);
> > WRITE_ONCE(*rsclp->tails[RCU_DONE_TAIL], NULL);
> > @@ -314,6 +325,7 @@ void rcu_segcblist_extract_done_cbs(struct
> > rcu_segcblist *rsclp,
> > for (i = RCU_CBLIST_NSEGS - 1; i >= RCU_DONE_TAIL; i--)
> > if (rsclp->tails[i] == rsclp->tails[RCU_DONE_TAIL])
> > WRITE_ONCE(rsclp->tails[i], &rsclp->head);
> > + rcu_segcblist_set_seglen(rsclp, RCU_DONE_TAIL, 0);
> > }
> >
> > /*
> > @@ -330,11 +342,16 @@ void rcu_segcblist_extract_pend_cbs(struct
> > rcu_segcblist *rsclp,
> >
> > if (!rcu_segcblist_pend_cbs(rsclp))
> > return; /* Nothing to do. */
> > + rclp->len = rcu_segcblist_get_seglen(rsclp, RCU_WAIT_TAIL) +
> > + rcu_segcblist_get_seglen(rsclp, RCU_NEXT_READY_TAIL) +
> > + rcu_segcblist_get_seglen(rsclp, RCU_NEXT_TAIL);
> > *rclp->tail = *rsclp->tails[RCU_DONE_TAIL];
> > rclp->tail = rsclp->tails[RCU_NEXT_TAIL];
> > WRITE_ONCE(*rsclp->tails[RCU_DONE_TAIL], NULL);
> > - for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++)
> > + for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++) {
> > WRITE_ONCE(rsclp->tails[i], rsclp->tails[RCU_DONE_TAIL]);
> > + rcu_segcblist_set_seglen(rsclp, i, 0);
>
> You seem to have forgotten the suggestion?
>
> rclp->len += rcu_segcblist_get_seglen(rsclp, i)
I decided to keep it this way as I did not see how it could be better.
You mentioned you are Ok with either option so I left it as is.
Thanks!
- Joel
---8<-----------------------
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 0f23d20d485a..79b7081143a7 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1160,6 +1160,7 @@ static void srcu_advance_state(struct srcu_struct *ssp)
*/
static void srcu_invoke_callbacks(struct work_struct *work)
{
+ long len;
bool more;
struct rcu_cblist ready_cbs;
struct rcu_head *rhp;
@@ -1182,6 +1183,7 @@ static void srcu_invoke_callbacks(struct work_struct
*work)
/* We are on the job! Extract and invoke ready callbacks. */
sdp->srcu_cblist_invoking = true;
rcu_segcblist_extract_done_cbs(&sdp->srcu_cblist, &ready_cbs);
+ len = ready_cbs.len;
spin_unlock_irq_rcu_node(sdp);
rhp = rcu_cblist_dequeue(&ready_cbs);
for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
@@ -1190,13 +1192,14 @@ static void srcu_invoke_callbacks(struct work_struct
*work)
rhp->func(rhp);
local_bh_enable();
}
+ WARN_ON_ONCE(ready_cbs.len);
/*
* Update counts, accelerate new callbacks, and if needed,
* schedule another round of callback invocation.
*/
spin_lock_irq_rcu_node(sdp);
- rcu_segcblist_insert_count(&sdp->srcu_cblist, &ready_cbs);
+ rcu_segcblist_add_len(&sdp->srcu_cblist, -len);
(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
rcu_seq_snap(&ssp->srcu_gp_seq));
sdp->srcu_cblist_invoking = false;
