On Wed, Jul 26, 2017 at 06:58:00PM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
>
> 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 <rgoldwyn@xxxxxxxx>
> ---
> 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
> + 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?
> goto retry_write;
> }
>
> --
> 2.12.3
>
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