On 08/08/2017 03:39 PM, Shaohua Li wrote:
> On Wed, Jul 26, 2017 at 06:58:00PM -0500, Goldwyn Rodrigues wrote:
>> From: Goldwyn Rodrigues <rgold...@suse.com>
>>
>> The RAID1 driver would bail with EAGAIN in case of:
>>  + I/O has to wait for a barrier
>>  + array is frozen
>>  + Area is suspended
>>  + There are too many pending I/O that it will be queued.
>>
>> To facilitate error for wait barriers, wait_barrier() is
>> returning bool. True in case if there was a wait (or is not
>> required). False in case a wait was required, but was not performed.
>>
>> Signed-off-by: Goldwyn Rodrigues <rgold...@suse.com>
>> ---
>>  drivers/md/raid1.c | 74 
>> +++++++++++++++++++++++++++++++++++++++++-------------
>>  1 file changed, 57 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
>> index 3febfc8391fb..66ca4288e3e8 100644
>> --- a/drivers/md/raid1.c
>> +++ b/drivers/md/raid1.c
>> @@ -903,8 +903,9 @@ static void lower_barrier(struct r1conf *conf, sector_t 
>> sector_nr)
>>      wake_up(&conf->wait_barrier);
>>  }
>>  
>> -static void _wait_barrier(struct r1conf *conf, int idx)
>> +static bool _wait_barrier(struct r1conf *conf, int idx, bool nowait)
>>  {
>> +    bool ret = true;
>>      /*
>>       * We need to increase conf->nr_pending[idx] very early here,
>>       * then raise_barrier() can be blocked when it waits for
>> @@ -935,7 +936,7 @@ static void _wait_barrier(struct r1conf *conf, int idx)
>>       */
>>      if (!READ_ONCE(conf->array_frozen) &&
>>          !atomic_read(&conf->barrier[idx]))
>> -            return;
>> +            return ret;
>>  
>>      /*
>>       * After holding conf->resync_lock, conf->nr_pending[idx]
>> @@ -953,18 +954,26 @@ static void _wait_barrier(struct r1conf *conf, int idx)
>>       */
>>      wake_up(&conf->wait_barrier);
>>      /* Wait for the barrier in same barrier unit bucket to drop. */
>> -    wait_event_lock_irq(conf->wait_barrier,
>> -                        !conf->array_frozen &&
>> -                         !atomic_read(&conf->barrier[idx]),
>> -                        conf->resync_lock);
>> +    if (conf->array_frozen || atomic_read(&conf->barrier[idx])) {
>> +            if (nowait)
>> +                    ret = false;
> 
> In this case, we nr_pending shouldn't be increased

Ok, will fix this.

> 
>> +            else
>> +                    wait_event_lock_irq(conf->wait_barrier,
>> +                                    !conf->array_frozen &&
>> +                                    !atomic_read(&conf->barrier[idx]),
>> +                                    conf->resync_lock);
>> +    }
>>      atomic_inc(&conf->nr_pending[idx]);
>>      atomic_dec(&conf->nr_waiting[idx]);
>>      spin_unlock_irq(&conf->resync_lock);
>> +    return ret;
>>  }
>>  
>> -static void wait_read_barrier(struct r1conf *conf, sector_t sector_nr)
>> +static bool wait_read_barrier(struct r1conf *conf, sector_t sector_nr,
>> +            bool nowait)
>>  {
>>      int idx = sector_to_idx(sector_nr);
>> +    bool ret = true;
>>  
>>      /*
>>       * Very similar to _wait_barrier(). The difference is, for read
>> @@ -976,7 +985,7 @@ static void wait_read_barrier(struct r1conf *conf, 
>> sector_t sector_nr)
>>      atomic_inc(&conf->nr_pending[idx]);
>>  
>>      if (!READ_ONCE(conf->array_frozen))
>> -            return;
>> +            return ret;
>>  
>>      spin_lock_irq(&conf->resync_lock);
>>      atomic_inc(&conf->nr_waiting[idx]);
>> @@ -987,19 +996,28 @@ static void wait_read_barrier(struct r1conf *conf, 
>> sector_t sector_nr)
>>       */
>>      wake_up(&conf->wait_barrier);
>>      /* Wait for array to be unfrozen */
>> -    wait_event_lock_irq(conf->wait_barrier,
>> -                        !conf->array_frozen,
>> -                        conf->resync_lock);
>> +    if (conf->array_frozen) {
>> +            /* If nowait flag is set, return false to
>> +             * show we did not wait
>> +             */
>> +            if (nowait)
>> +                    ret = false;
> 
> ditto
>> +            else
>> +                    wait_event_lock_irq(conf->wait_barrier,
>> +                                    !conf->array_frozen,
>> +                                    conf->resync_lock);
>> +    }
>>      atomic_inc(&conf->nr_pending[idx]);
>>      atomic_dec(&conf->nr_waiting[idx]);
>>      spin_unlock_irq(&conf->resync_lock);
>> +    return ret;
>>  }
>>  
>> -static void wait_barrier(struct r1conf *conf, sector_t sector_nr)
>> +static bool wait_barrier(struct r1conf *conf, sector_t sector_nr, bool 
>> nowait)
>>  {
>>      int idx = sector_to_idx(sector_nr);
>>  
>> -    _wait_barrier(conf, idx);
>> +    return _wait_barrier(conf, idx, nowait);
>>  }
>>  
>>  static void wait_all_barriers(struct r1conf *conf)
>> @@ -1007,7 +1025,7 @@ static void wait_all_barriers(struct r1conf *conf)
>>      int idx;
>>  
>>      for (idx = 0; idx < BARRIER_BUCKETS_NR; idx++)
>> -            _wait_barrier(conf, idx);
>> +            _wait_barrier(conf, idx, false);
>>  }
>>  
>>  static void _allow_barrier(struct r1conf *conf, int idx)
>> @@ -1223,7 +1241,11 @@ static void raid1_read_request(struct mddev *mddev, 
>> struct bio *bio,
>>       * Still need barrier for READ in case that whole
>>       * array is frozen.
>>       */
>> -    wait_read_barrier(conf, bio->bi_iter.bi_sector);
>> +    if (!wait_read_barrier(conf, bio->bi_iter.bi_sector,
>> +                            bio->bi_opf & REQ_NOWAIT)) {
>> +            bio_wouldblock_error(bio);
>> +            return;
>> +    }
>>  
>>      if (!r1_bio)
>>              r1_bio = alloc_r1bio(mddev, bio);
>> @@ -1333,6 +1355,11 @@ static void raid1_write_request(struct mddev *mddev, 
>> struct bio *bio,
>>               * an interruptible wait.
>>               */
>>              DEFINE_WAIT(w);
>> +            if (bio->bi_opf & REQ_NOWAIT) {
>> +                    bio_wouldblock_error(bio);
>> +                    return;
>> +            }
>> +
>>              for (;;) {
>>                      sigset_t full, old;
>>                      prepare_to_wait(&conf->wait_barrier,
>> @@ -1351,7 +1378,11 @@ static void raid1_write_request(struct mddev *mddev, 
>> struct bio *bio,
>>              }
>>              finish_wait(&conf->wait_barrier, &w);
>>      }
>> -    wait_barrier(conf, bio->bi_iter.bi_sector);
>> +    if (!wait_barrier(conf, bio->bi_iter.bi_sector,
>> +                            bio->bi_opf & REQ_NOWAIT)) {
>> +            bio_wouldblock_error(bio);
>> +            return;
>> +    }
>>  
>>      r1_bio = alloc_r1bio(mddev, bio);
>>      r1_bio->sectors = max_write_sectors;
>> @@ -1359,6 +1390,10 @@ static void raid1_write_request(struct mddev *mddev, 
>> struct bio *bio,
>>      if (conf->pending_count >= max_queued_requests) {
>>              md_wakeup_thread(mddev->thread);
>>              raid1_log(mddev, "wait queued");
>> +            if (bio->bi_opf & REQ_NOWAIT) {
>> +                    bio_wouldblock_error(bio);
>> +                    return;
>> +            }
>>              wait_event(conf->wait_barrier,
>>                         conf->pending_count < max_queued_requests);
>>      }
>> @@ -1442,6 +1477,11 @@ static void raid1_write_request(struct mddev *mddev, 
>> struct bio *bio,
>>              /* Wait for this device to become unblocked */
>>              int j;
>>  
>> +            if (bio->bi_opf & REQ_NOWAIT) {
>> +                    bio_wouldblock_error(bio);
>> +                    return;
>> +            }
>> +
>>              for (j = 0; j < i; j++)
>>                      if (r1_bio->bios[j])
>>                              rdev_dec_pending(conf->mirrors[j].rdev, mddev);
>> @@ -1449,7 +1489,7 @@ static void raid1_write_request(struct mddev *mddev, 
>> struct bio *bio,
>>              allow_barrier(conf, bio->bi_iter.bi_sector);
>>              raid1_log(mddev, "wait rdev %d blocked", 
>> blocked_rdev->raid_disk);
>>              md_wait_for_blocked_rdev(blocked_rdev, mddev);
>> -            wait_barrier(conf, bio->bi_iter.bi_sector);
>> +            wait_barrier(conf, bio->bi_iter.bi_sector, false);
> 
> There are other cases we could block, for example, md_wait_for_blocked_rdev
> here. Is the goal just avoid block for normal situations?

Isn't this covered by the if condition of the codeblock (blocked_rdev !=
NULL)?

> 
>>              goto retry_write;
>>      }
>>  
>> -- 
>> 2.12.3
>>
>> --
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-- 
Goldwyn

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