[md PATCH 02/15] md/raid5: simplfy delaying of writes while metadata is updated.

NeilBrown
2017-03-15T03:05:12Z

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.
As this change can leave a stripe_head ready for handling immediately
after handle_active_stripes() returns, we change raid5_do_work() to
pause when MD_CHANGE_PENDING is set, so that it doesn't spin.

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 | 31 ++++++++-----------------------
drivers/md/raid5.h | 3 ---
2 files changed, 8 insertions(+), 26 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index cc2d039b4aae..f990f74901d2 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4690,7 +4690,8 @@ 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;
}
@@ -5020,15 +5021,8 @@ 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);
}
@@ -6225,6 +6219,7 @@ static void raid5_do_work(struct work_struct *work)
struct r5worker *worker = container_of(work, struct r5worker, work);
struct r5worker_group *group = worker->group;
struct r5conf *conf = group->conf;
+ struct mddev *mddev = conf->mddev;
int group_id = group - conf->worker_groups;
int handled;
struct blk_plug plug;
@@ -6245,6 +6240,9 @@ static void raid5_do_work(struct work_struct *work)
if (!batch_size && !released)
break;
handled += batch_size;
+ wait_event_lock_irq(mddev->sb_wait,
+ !test_bit(MD_SB_CHANGE_DEVS, &mddev->sb_flags),
+ conf->device_lock);
}
pr_debug("%d stripes handled\n", handled);

@@ -6272,18 +6270,6 @@ 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);
@@ -6935,7 +6921,6 @@ 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 ba5b7a3790af..13800dc9dd88 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -638,9 +638,6 @@ 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.