On Tue, Jan 24, 2017 at 10:45:30AM -0800, Song Liu wrote:
> 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.
Applied, thanks! I did a slight change: replaced flush_scheduled_work with flush_work
> Signed-off-by: Song Liu <songliubraving@xxxxxx>
> ---
> drivers/md/raid5-cache.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
> drivers/md/raid5.c | 15 ++++++++-------
> drivers/md/raid5.h | 2 ++
> 3 files changed, 56 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
> index 00d2838..8ab6e1a 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_info("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 +2328,10 @@ static ssize_t r5c_journal_mode_store(struct mddev *mddev,
> val > R5C_JOURNAL_MODE_WRITE_BACK)
> return -EINVAL;
>
> + if (raid5_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 +2390,16 @@ 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 +2744,19 @@ 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 (raid5_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 +2832,7 @@ 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);
> @@ -2820,6 +2865,7 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
>
> void r5l_exit_log(struct r5l_log *log)
> {
> + flush_scheduled_work();
> md_unregister_thread(&log->reclaim_thread);
> mempool_destroy(log->meta_pool);
> bioset_free(log->bs);
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index ad8f24c..9c93ca1 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 raid5_calc_degraded(struct r5conf *conf)
> {
> int degraded, degraded2;
> int i;
> @@ -619,7 +619,7 @@ static int has_failed(struct r5conf *conf)
> if (conf->mddev->reshape_position == MaxSector)
> return conf->mddev->degraded > conf->max_degraded;
>
> - degraded = calc_degraded(conf);
> + degraded = raid5_calc_degraded(conf);
> if (degraded > conf->max_degraded)
> return 1;
> return 0;
> @@ -2592,7 +2592,7 @@ static void raid5_error(struct mddev *mddev, struct md_rdev *rdev)
>
> spin_lock_irqsave(&conf->device_lock, flags);
> clear_bit(In_sync, &rdev->flags);
> - mddev->degraded = calc_degraded(conf);
> + mddev->degraded = raid5_calc_degraded(conf);
> spin_unlock_irqrestore(&conf->device_lock, flags);
> set_bit(MD_RECOVERY_INTR, &mddev->recovery);
>
> @@ -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);
> }
>
> /*
> @@ -7147,7 +7148,7 @@ static int raid5_run(struct mddev *mddev)
> /*
> * 0 for a fully functional array, 1 or 2 for a degraded array.
> */
> - mddev->degraded = calc_degraded(conf);
> + mddev->degraded = raid5_calc_degraded(conf);
>
> if (has_failed(conf)) {
> pr_crit("md/raid:%s: not enough operational devices (%d/%d failed)\n",
> @@ -7394,7 +7395,7 @@ static int raid5_spare_active(struct mddev *mddev)
> }
> }
> spin_lock_irqsave(&conf->device_lock, flags);
> - mddev->degraded = calc_degraded(conf);
> + mddev->degraded = raid5_calc_degraded(conf);
> spin_unlock_irqrestore(&conf->device_lock, flags);
> print_raid5_conf(conf);
> return count;
> @@ -7754,7 +7755,7 @@ static int raid5_start_reshape(struct mddev *mddev)
> * pre and post number of devices.
> */
> spin_lock_irqsave(&conf->device_lock, flags);
> - mddev->degraded = calc_degraded(conf);
> + mddev->degraded = raid5_calc_degraded(conf);
> spin_unlock_irqrestore(&conf->device_lock, flags);
> }
> mddev->raid_disks = conf->raid_disks;
> @@ -7842,7 +7843,7 @@ static void raid5_finish_reshape(struct mddev *mddev)
> } else {
> int d;
> spin_lock_irq(&conf->device_lock);
> - mddev->degraded = calc_degraded(conf);
> + mddev->degraded = raid5_calc_degraded(conf);
> spin_unlock_irq(&conf->device_lock);
> for (d = conf->raid_disks ;
> d < conf->raid_disks - mddev->delta_disks;
> diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
> index 8ae498c..bbdc5a4 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 raid5_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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