On Wed, Mar 29, 2017 at 01:00:13AM -0700, Song Liu wrote:
> For the raid456 with writeback cache, when journal device failed during
> normal operation, it is still possible to persist all data, as all
> pending data is still in stripe cache. However, it is necessary to handle
> journal failure gracefully.
>
> During journal failures, this patch makes the follow changes to land data
> in cache to raid disks gracefully:
>
> 1. In raid5_remove_disk(), flush all cached stripes;
> 2. In handle_stripe(), allow stripes with data in journal (s.injournal > 0)
> to make progress;
> 3. In delay_towrite(), only process data in the cache (skip dev->towrite);
> 4. In __get_priority_stripe(), set try_loprio to true, so no stripe stuck
> in loprio_list
> 5. In r5l_do_submit_io(), submit io->split_bio first (see inline comments
> for details).
> Signed-off-by: Song Liu <songliubraving@xxxxxx>
> ---
> drivers/md/raid5-cache.c | 27 ++++++++++++++++++---------
> drivers/md/raid5.c | 28 ++++++++++++++++++++++++----
> 2 files changed, 42 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
> index b6194e0..0838617 100644
> --- a/drivers/md/raid5-cache.c
> +++ b/drivers/md/raid5-cache.c
> @@ -632,20 +632,29 @@ static void r5l_do_submit_io(struct r5l_log *log, struct r5l_io_unit *io)
> __r5l_set_io_unit_state(io, IO_UNIT_IO_START);
> spin_unlock_irqrestore(&log->io_list_lock, flags);
>
> + /*
> + * In case of journal device failures, submit_bio will get error
> + * and calls endio, then active stripes will continue write
> + * process. Therefore, it is not necessary to check Faulty bit
> + * of journal device here.
> + *
> + * However, calling r5l_log_endio(current_bio) may change
> + * split_bio. Therefore, it is necessary to check split_bio before
> + * submit current_bio.
> + */
sorry, for the delay. what did you mean 'calling r5l_log_endio may change
split_bio'? The split_bio is chained into current_bio. The endio of
current_bio(r5l_log_endio) is only called after all chained bio completion. I
didn't get the point why this change.
> + if (io->split_bio) {
> + if (io->has_flush)
> + io->split_bio->bi_opf |= REQ_PREFLUSH;
> + if (io->has_fua)
> + io->split_bio->bi_opf |= REQ_FUA;
> + submit_bio(io->split_bio);
> + }
> +
> if (io->has_flush)
> io->current_bio->bi_opf |= REQ_PREFLUSH;
> if (io->has_fua)
> io->current_bio->bi_opf |= REQ_FUA;
> submit_bio(io->current_bio);
> -
> - if (!io->split_bio)
> - return;
> -
> - if (io->has_flush)
> - io->split_bio->bi_opf |= REQ_PREFLUSH;
> - if (io->has_fua)
> - io->split_bio->bi_opf |= REQ_FUA;
> - submit_bio(io->split_bio);
> }
>
> /* deferred io_unit will be dispatched here */
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 6036d5e..4d3d1ab 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -3054,6 +3054,11 @@ sector_t raid5_compute_blocknr(struct stripe_head *sh, int i, int previous)
> * When LOG_CRITICAL, stripes with injournal == 0 will be sent to
> * no_space_stripes list.
> *
> + * 3. during journal failure
> + * In journal failure, we try to flush all cached data to raid disks
> + * based on data in stripe cache. The array is read-only to upper
> + * layers, so we would skip all pending writes.
> + *
> */
> static inline bool delay_towrite(struct r5conf *conf,
> struct r5dev *dev,
> @@ -3067,6 +3072,9 @@ static inline bool delay_towrite(struct r5conf *conf,
> if (test_bit(R5C_LOG_CRITICAL, &conf->cache_state) &&
> s->injournal > 0)
> return true;
> + /* case 3 above */
> + if (s->log_failed && s->injournal)
> + return true;
> return false;
> }
>
> @@ -4689,10 +4697,15 @@ static void handle_stripe(struct stripe_head *sh)
> " to_write=%d failed=%d failed_num=%d,%d\n",
> s.locked, s.uptodate, s.to_read, s.to_write, s.failed,
> s.failed_num[0], s.failed_num[1]);
> - /* check if the array has lost more than max_degraded devices and,
> + /*
> + * check if the array has lost more than max_degraded devices and,
> * if so, some requests might need to be failed.
> + *
> + * When journal device failed (log_failed), we will only process
> + * the stripe if there is data need write to raid disks
> */
> - if (s.failed > conf->max_degraded || s.log_failed) {
> + if (s.failed > conf->max_degraded ||
> + (s.log_failed && s.injournal == 0)) {
> sh->check_state = 0;
> sh->reconstruct_state = 0;
> break_stripe_batch_list(sh, 0);
> @@ -5272,7 +5285,8 @@ static struct stripe_head *__get_priority_stripe(struct r5conf *conf, int group)
> struct list_head *handle_list = NULL;
> struct r5worker_group *wg;
> bool second_try = !r5c_is_writeback(conf->log);
> - bool try_loprio = test_bit(R5C_LOG_TIGHT, &conf->cache_state);
> + bool try_loprio = test_bit(R5C_LOG_TIGHT, &conf->cache_state) ||
> + r5l_log_disk_error(conf);
>
> again:
> wg = NULL;
> @@ -7526,6 +7540,7 @@ static int raid5_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
> int number = rdev->raid_disk;
> struct md_rdev **rdevp;
> struct disk_info *p = conf->disks + number;
> + unsigned long flags;
>
> print_raid5_conf(conf);
> if (test_bit(Journal, &rdev->flags) && conf->log) {
> @@ -7535,7 +7550,12 @@ static int raid5_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
> * neilb: there is no locking about new writes here,
> * so this cannot be safe.
> */
> - if (atomic_read(&conf->active_stripes)) {
> + if (atomic_read(&conf->active_stripes) ||
> + atomic_read(&conf->r5c_cached_full_stripes) ||
> + atomic_read(&conf->r5c_cached_partial_stripes)) {
> + spin_lock_irqsave(&conf->device_lock, flags);
> + r5c_flush_cache(conf, INT_MAX);
> + spin_unlock_irqrestore(&conf->device_lock, flags);
> return -EBUSY;
It's weird this is called in raid5_remove_disk, shouldn't this be called in log
disk error in case user doesn't remove the log disk? And this is a policy
change. User might not want to do the flush, as this exposes write hole. I
think at least we should print info out here to warn user the flush.
Thanks,
Shaohua
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