[md PATCH 02/14] md/raid5: simplfy delaying of writes while metadata is updated.

NeilBrown
2017-02-16T04:39:01Z

If a device fails during a write, we must ensure the failure is
recorded in the metadata before the completion of the write is
acknowleged.

Commit c3cce6cda162 ("md/raid5: ensure device failure recorded before
write request returns.") added code for this, but it was
unnecessarily complicated. We already had similar functionality for
handling updates to the bad-block-list, thanks to Commit de393cdea66c
("md: make it easier to wait for bad blocks to be acknowledged.")

So revert most of the former commit, and instead avoid collecting
completed writes if MD_CHANGE_PENDING is set. raid5d() will then flush
the metadata and retry the stripe_head.

We check MD_CHANGE_PENDING *after* analyse_stripe() as it could be set
asynchronously. After analyse_stripe(), we have collected stable data
about the state of devices, which will be used to make decisions.

Signed-off-by: NeilBrown <neilb@suse.com>
---
drivers/md/raid5.c | 27 ++++-----------------------
drivers/md/raid5.h | 3 ---
2 files changed, 4 insertions(+), 26 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 760b726943c9..154593e0afbe 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4492,7 +4492,8 @@ static void handle_stripe(struct stripe_head *sh)
if (test_bit(STRIPE_LOG_TRAPPED, &sh->state))
goto finish;

- if (s.handle_bad_blocks) {
+ if (s.handle_bad_blocks ||
+ test_bit(MD_SB_CHANGE_PENDING, &conf->mddev->sb_flags)) {
set_bit(STRIPE_HANDLE, &sh->state);
goto finish;
}
@@ -4822,15 +4823,8 @@ static void handle_stripe(struct stripe_head *sh)
md_wakeup_thread(conf->mddev->thread);
}

- if (!bio_list_empty(&s.return_bi)) {
- if (test_bit(MD_SB_CHANGE_PENDING, &conf->mddev->sb_flags)) {
- spin_lock_irq(&conf->device_lock);
- bio_list_merge(&conf->return_bi, &s.return_bi);
- spin_unlock_irq(&conf->device_lock);
- md_wakeup_thread(conf->mddev->thread);
- } else
- return_io(&s.return_bi);
- }
+ if (!bio_list_empty(&s.return_bi))
+ return_io(&s.return_bi);

clear_bit_unlock(STRIPE_ACTIVE, &sh->state);
}
@@ -6055,18 +6049,6 @@ static void raid5d(struct md_thread *thread)

md_check_recovery(mddev);

- if (!bio_list_empty(&conf->return_bi) &&
- !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags)) {
- struct bio_list tmp = BIO_EMPTY_LIST;
- spin_lock_irq(&conf->device_lock);
- if (!test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags)) {
- bio_list_merge(&tmp, &conf->return_bi);
- bio_list_init(&conf->return_bi);
- }
- spin_unlock_irq(&conf->device_lock);
- return_io(&tmp);
- }
-
blk_start_plug(&plug);
handled = 0;
spin_lock_irq(&conf->device_lock);
@@ -6705,7 +6687,6 @@ static struct r5conf *setup_conf(struct mddev *mddev)
INIT_LIST_HEAD(&conf->hold_list);
INIT_LIST_HEAD(&conf->delayed_list);
INIT_LIST_HEAD(&conf->bitmap_list);
- bio_list_init(&conf->return_bi);
init_llist_head(&conf->released_stripes);
atomic_set(&conf->active_stripes, 0);
atomic_set(&conf->preread_active_stripes, 0);
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 1440fa26e296..1ef71273b9b2 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -621,9 +621,6 @@ struct r5conf {
int skip_copy; /* Don't copy data from bio to stripe cache */
struct list_head *last_hold; /* detect hold_list promotions */

- /* bios to have bi_end_io called after metadata is synced */
- struct bio_list return_bi;
-
atomic_t reshape_stripes; /* stripes with pending writes for reshape */
/* unfortunately we need two cache names as we temporarily have
* two caches.