Re: 2.6.10-rc2-bk7 - Badness in cfq_put_request at drivers/block/cfq-iosched.c:1402

Jens Axboe
2004-11-27T07:19:14Z

On Fri, Nov 26 2004, Jens Axboe wrote:
> On Thu, Nov 25 2004, Jens Axboe wrote:
> > On Wed, Nov 24 2004, Christopher S. Aker wrote:
> > > > Can you try this simple check to see if it triggers anything?
> > > >
> > > > ===== cfq-iosched.c 1.13 vs edited =====
> > > > --- 1.13/drivers/block/cfq-iosched.c 2004-10-30 01:35:21 +02:00
> > > > +++ edited/cfq-iosched.c 2004-11-24 14:40:13 +01:00
> > > > @@ -1389,6 +1389,8 @@
> > > > struct cfq_data *cfqd = q->elevator->elevator_data;
> > > > struct cfq_rq *crq = RQ_DATA(rq);
> > > >
> > > > + WARN_ON(!spin_is_locked(q->queue_lock));
> > > > +
> > > > if (crq) {
> > > > struct cfq_queue *cfqq = crq->cfq_queue;
> > >
> > > I'd be happy to, but I won't have a free machine for a couple of days.
> > > I'll can probably give it a shot during the weekend...
> >
> > Nevermind, here's a patch to fix it. I was so focused on the decrement
> > side of things that I forgot to check the increment, pretty silly error
> > really.
>
> And a small fix is needed on top of that, in case of hash type changes
> (writing to hash_key).

... And that one relied on another hashing change I made locally. 3rd
time is the charm,.

Signed-off-by: Jens Axboe <axboe@suse.de>

===== drivers/block/cfq-iosched.c 1.13 vs edited =====
--- 1.13/drivers/block/cfq-iosched.c 2004-10-30 01:35:21 +02:00
+++ edited/drivers/block/cfq-iosched.c 2004-11-26 09:06:38 +01:00
@@ -1398,10 +1398,7 @@
if (crq->io_context)
put_io_context(crq->io_context->ioc);

- if (!cfqq->allocated[crq->is_write]) {
- WARN_ON(1);
- cfqq->allocated[crq->is_write] = 1;
- }
+ BUG_ON(!cfqq->allocated[crq->is_write]);
cfqq->allocated[crq->is_write]--;

mempool_free(crq, cfqd->crq_pool);
@@ -1421,7 +1418,7 @@
struct cfq_data *cfqd = q->elevator->elevator_data;
struct cfq_io_context *cic;
const int rw = rq_data_dir(rq);
- struct cfq_queue *cfqq;
+ struct cfq_queue *cfqq, *saved_cfqq;
struct cfq_rq *crq;
unsigned long flags;

@@ -1439,20 +1436,30 @@
#endif
}

+repeat:
if (cfqq->allocated[rw] >= cfqd->max_queued)
goto out_lock;

+ cfqq->allocated[rw]++;
spin_unlock_irqrestore(q->queue_lock, flags);

/*
- * if hashing type has changed, the cfq_queue might change here. we
- * don't bother rechecking ->allocated since it should be a rare
- * event
+ * if hashing type has changed, the cfq_queue might change here.
*/
+ saved_cfqq = cfqq;
cic = cfq_get_io_context(&cfqq, gfp_mask);
if (!cic)
goto err;

+ /*
+ * repeat allocation checks on queue change
+ */
+ if (unlikely(saved_cfqq != cfqq)) {
+ spin_lock_irqsave(q->queue_lock, flags);
+ saved_cfqq->allocated[rw]--;
+ goto repeat;
+ }
+
crq = mempool_alloc(cfqd->crq_pool, gfp_mask);
if (crq) {
RB_CLEAR(&crq->rb_node);
@@ -1465,7 +1472,6 @@
crq->in_flight = crq->accounted = crq->is_sync = 0;
crq->is_write = rw;
rq->elevator_private = crq;
- cfqq->allocated[rw]++;
cfqq->alloc_limit[rw] = 0;
return 0;
}
@@ -1473,6 +1479,7 @@
put_io_context(cic->ioc);
err:
spin_lock_irqsave(q->queue_lock, flags);
+ cfqq->allocated[rw]--;
cfq_put_queue(cfqq);
out_lock:
spin_unlock_irqrestore(q->queue_lock, flags);

--
Jens Axboe