write-back cache in degraded mode introduces corner cases to the array.
Although we try to cover all these corner cases, it is safer to just
disable write-back cache when the array is in degraded mode.
In this patch, we disable writeback cache for degraded mode:
1. On device failure, if the array enters degraded mode, raid5_error()
will submit async job r5c_disable_writeback_async to disable
writeback;
2. In r5c_journal_mode_store(), it is invalid to enable writeback in
degraded mode;
3. In r5c_try_caching_write(), stripes with s->failed>0 will be handled
in write-through mode.
Signed-off-by: Song Liu <songliubraving@xxxxxx>
---
drivers/md/raid5-cache.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
drivers/md/raid5.c | 3 ++-
drivers/md/raid5.h | 2 ++
3 files changed, 48 insertions(+), 1 deletion(-)
diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 00d2838..55f1a37 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -164,6 +164,9 @@ struct r5l_log {
/* to submit async io_units, to fulfill ordering of flush */
struct work_struct deferred_io_work;
+ /* to disable write back during in degraded mode */
+ struct work_struct disable_writeback_work;
+
/* to for chunk_aligned_read in writeback mode, details below */
spinlock_t tree_lock;
struct radix_tree_root big_stripe_tree;
@@ -653,6 +656,20 @@ static void r5l_submit_io_async(struct work_struct *work)
r5l_do_submit_io(log, io);
}
+static void r5c_disable_writeback_async(struct work_struct *work)
+{
+ struct r5l_log *log = container_of(work, struct r5l_log,
+ disable_writeback_work);
+ struct mddev *mddev = log->rdev->mddev;
+ struct r5conf *conf = mddev->private;
+
+ pr_crit("md/raid:%s: Disabling writeback cache for degraded array.\n",
+ mdname(mddev));
+ mddev_suspend(mddev);
+ conf->log->r5c_journal_mode = R5C_JOURNAL_MODE_WRITE_THROUGH;
+ mddev_resume(mddev);
+}
+
static void r5l_submit_current_io(struct r5l_log *log)
{
struct r5l_io_unit *io = log->current_io;
@@ -2311,6 +2328,9 @@ static ssize_t r5c_journal_mode_store(struct mddev *mddev,
val > R5C_JOURNAL_MODE_WRITE_BACK)
return -EINVAL;
+ if (calc_degraded(conf) > 0 && val == R5C_JOURNAL_MODE_WRITE_BACK)
+ return -EINVAL;
+
mddev_suspend(mddev);
conf->log->r5c_journal_mode = val;
mddev_resume(mddev);
@@ -2369,6 +2389,16 @@ int r5c_try_caching_write(struct r5conf *conf,
set_bit(STRIPE_R5C_CACHING, &sh->state);
}
+ /*
+ * When run in degraded mode, array is set to write-through mode.
+ * This check helps drain pending write safely in the transition to
+ * write-through mode.
+ */
+ if (s->failed) {
+ r5c_make_stripe_write_out(sh);
+ return -EAGAIN;
+ }
+
for (i = disks; i--; ) {
dev = &sh->dev[i];
/* if non-overwrite, use writing-out phase */
@@ -2713,6 +2743,19 @@ static int r5l_load_log(struct r5l_log *log)
return ret;
}
+void r5c_update_on_rdev_error(struct mddev *mddev)
+{
+ struct r5conf *conf = mddev->private;
+ struct r5l_log *log = conf->log;
+
+ if (!log)
+ return;
+
+ if (calc_degraded(conf) > 0 &&
+ conf->log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_BACK)
+ schedule_work(&log->disable_writeback_work);
+}
+
int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
{
struct request_queue *q = bdev_get_queue(rdev->bdev);
@@ -2788,6 +2831,7 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
spin_lock_init(&log->no_space_stripes_lock);
INIT_WORK(&log->deferred_io_work, r5l_submit_io_async);
+ INIT_WORK(&log->disable_writeback_work, r5c_disable_writeback_async);
log->r5c_journal_mode = R5C_JOURNAL_MODE_WRITE_THROUGH;
INIT_LIST_HEAD(&log->stripe_in_journal_list);
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index ad8f24c..f8223e5 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -556,7 +556,7 @@ static struct stripe_head *__find_stripe(struct r5conf *conf, sector_t sector,
* of the two sections, and some non-in_sync devices may
* be insync in the section most affected by failed devices.
*/
-static int calc_degraded(struct r5conf *conf)
+int calc_degraded(struct r5conf *conf)
{
int degraded, degraded2;
int i;
@@ -2606,6 +2606,7 @@ static void raid5_error(struct mddev *mddev, struct md_rdev *rdev)
bdevname(rdev->bdev, b),
mdname(mddev),
conf->raid_disks - mddev->degraded);
+ r5c_update_on_rdev_error(mddev);
}
/*
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 8ae498c..36f28d1 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -762,6 +762,7 @@ extern sector_t raid5_compute_sector(struct r5conf *conf, sector_t r_sector,
extern struct stripe_head *
raid5_get_active_stripe(struct r5conf *conf, sector_t sector,
int previous, int noblock, int noquiesce);
+extern int calc_degraded(struct r5conf *conf);
extern int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev);
extern void r5l_exit_log(struct r5l_log *log);
extern int r5l_write_stripe(struct r5l_log *log, struct stripe_head *head_sh);
@@ -791,4 +792,5 @@ extern void r5c_check_stripe_cache_usage(struct r5conf *conf);
extern void r5c_check_cached_full_stripe(struct r5conf *conf);
extern struct md_sysfs_entry r5c_journal_mode;
extern bool r5c_big_stripe_cached(struct r5conf *conf, sector_t sect);
+extern void r5c_update_on_rdev_error(struct mddev *mddev);
#endif
--
2.9.3
--
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