Re: [PATCH] sbitmap: fix permanent io blocking caused by insufficient wakeup times

[Liu Song]

在 2022/9/17 18:20, Yu Kuai 写道:
> Hi,
>
> 在 2022/09/17 10:33, Liu Song 写道:
> > From: Liu Song <liusong@xxxxxxxxxxxxxxxxx>
> >
> > In "sbitmap_queue_clear_batch", a batch of completed requests may be
> > processed at once, but "wait_cnt" is only reduced once by
> > "sbitmap_queue_wake_up".
> > In our environment, if "/sys/block/nvme0n1/nr_requests" is adjusted to
> > 32, it is easily because no tag and then enter the waiting situation,
> > if continue change "nr_requests" to 1023 at this time, it will basically
> > fall into the situation of permanent blocking. Because there will be
> > "blk_freeze_queue" in "blk_mq_update_nr_requests", which will prevent
> > any new requests, but due to insufficient wake-up, there are tasks
> > waiting for wake-up, but no new wake-up opportunities will be generated
> > at this time, so this situation needs to be repaired.
>
> It seems Keith already fixed this recently. Can you have a check at his
> patch?
Hi

It's a bit embarrassing. My code is 6.0-rc3. Yesterday, there was a 
problem with
the Tsinghua mirror station. The fetched code could not be the latest, 
so I submitted it.
According to your suggestion, I checked and it has been fixed, thank you 
for your suggestion.

Thanks

> Thanks,
> Kuai
> > Signed-off-by: Liu Song <liusong@xxxxxxxxxxxxxxxxx>
> > ---
> >   include/linux/sbitmap.h |  8 ++++++++
> >   lib/sbitmap.c           | 22 ++++++++++++++++++----
> >   2 files changed, 26 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
> > index 8f5a86e..153382e 100644
> > --- a/include/linux/sbitmap.h
> > +++ b/include/linux/sbitmap.h
> > @@ -579,6 +579,14 @@ static inline struct sbq_wait_state 
> > *sbq_wait_ptr(struct sbitmap_queue *sbq,
> >   void sbitmap_queue_wake_up(struct sbitmap_queue *sbq);
> >     /**
> > + * sbitmap_queue_wake_up_batch() - Attempt to wake up waiters in 
> > batches
> > + * on a &struct sbitmap_queue.
> > + * @sbq: Bitmap queue to wake up.
> > + * @nr: The number of attempts to wake the waiter.
> > + */
> > +void sbitmap_queue_wake_up_batch(struct sbitmap_queue *sbq, int nr);
> > +
> > +/**
> >    * sbitmap_queue_show() - Dump &struct sbitmap_queue information to 
> > a &struct
> >    * seq_file.
> >    * @sbq: Bitmap queue to show.
> > diff --git a/lib/sbitmap.c b/lib/sbitmap.c
> > index 29eb048..f2aa1da 100644
> > --- a/lib/sbitmap.c
> > +++ b/lib/sbitmap.c
> > @@ -600,7 +600,7 @@ static struct sbq_wait_state *sbq_wake_ptr(struct 
> > sbitmap_queue *sbq)
> >       return NULL;
> >   }
> >   -static bool __sbq_wake_up(struct sbitmap_queue *sbq)
> > +static bool __sbq_wake_up(struct sbitmap_queue *sbq, int *nr)
> >   {
> >       struct sbq_wait_state *ws;
> >       unsigned int wake_batch;
> > @@ -610,6 +610,7 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq)
> >       if (!ws)
> >           return false;
> >   +again:
> >       wait_cnt = atomic_dec_return(&ws->wait_cnt);
> >       if (wait_cnt <= 0) {
> >           int ret;
> > @@ -632,10 +633,14 @@ static bool __sbq_wake_up(struct sbitmap_queue 
> > *sbq)
> >           if (ret == wait_cnt) {
> >               sbq_index_atomic_inc(&sbq->wake_index);
> >               wake_up_nr(&ws->wait, wake_batch);
> > -            return false;
> > +            if (!nr || *nr <= 0)
> > +                return false;
> >           }
> >             return true;
> > +    } else if (nr && *nr) {
> > +        (*nr)--;
> > +        goto again;
> >       }
> >         return false;
> > @@ -643,11 +648,20 @@ static bool __sbq_wake_up(struct sbitmap_queue 
> > *sbq)
> >     void sbitmap_queue_wake_up(struct sbitmap_queue *sbq)
> >   {
> > -    while (__sbq_wake_up(sbq))
> > +    while (__sbq_wake_up(sbq, NULL))
> >           ;
> >   }
> >   EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);
> >   +void sbitmap_queue_wake_up_batch(struct sbitmap_queue *sbq, int nr)
> > +{
> > +    int i = SBQ_WAIT_QUEUES;
> > +
> > +    while (__sbq_wake_up(sbq, &nr) && --i)
> > +        ;
> > +}
> > +EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up_batch);
> > +
> >   static inline void sbitmap_update_cpu_hint(struct sbitmap *sb, int 
> > cpu, int tag)
> >   {
> >       if (likely(!sb->round_robin && tag < sb->depth))
> > @@ -683,7 +697,7 @@ void sbitmap_queue_clear_batch(struct 
> > sbitmap_queue *sbq, int offset,
> >           atomic_long_andnot(mask, (atomic_long_t *) addr);
> >         smp_mb__after_atomic();
> > -    sbitmap_queue_wake_up(sbq);
> > +    sbitmap_queue_wake_up_batch(sbq, nr_tags);
> >       sbitmap_update_cpu_hint(&sbq->sb, raw_smp_processor_id(),
> >                       tags[nr_tags - 1] - offset);
> >   }