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Commit 2e38a37f authored by Song Liu's avatar Song Liu Committed by Shaohua Li
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md/r5cache: disable write back for degraded array 



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: default avatarSong Liu <songliubraving@fb.com>
Signed-off-by: default avatarShaohua Li <shli@fb.com>
parent 07e83364

drivers/md/raid5-cache.c

+46 −0
Original line number Diff line number Diff line
@@ -162,6 +162,8 @@ 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;

};



/*
@@ -611,6 +613,21 @@ 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;



	if (log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_THROUGH)

		return;

	pr_info("md/raid:%s: Disabling writeback cache for degraded array.\n",

		mdname(mddev));

	mddev_suspend(mddev);

	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;
@@ -2269,6 +2286,10 @@ 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);
@@ -2323,6 +2344,16 @@ 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 */
@@ -2579,6 +2610,19 @@ 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);
@@ -2651,6 +2695,7 @@ 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);
@@ -2683,6 +2728,7 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev) 


void r5l_exit_log(struct r5l_log *log)

{

	flush_work(&log->disable_writeback_work);

	md_unregister_thread(&log->reclaim_thread);

	mempool_destroy(log->meta_pool);

	bioset_free(log->bs);

drivers/md/raid5.c

+8 −7
Original line number Diff line number Diff line
@@ -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;
@@ -2555,7 +2555,7 @@ 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);
@@ -2569,6 +2569,7 @@ 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);

}



/*
@@ -7091,7 +7092,7 @@ 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",
@@ -7338,7 +7339,7 @@ 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;
@@ -7698,7 +7699,7 @@ 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;
@@ -7786,7 +7787,7 @@ 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;

drivers/md/raid5.h

+2 −0
Original line number Diff line number Diff line
@@ -758,6 +758,7 @@ 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);
@@ -786,4 +787,5 @@ extern void r5c_flush_cache(struct r5conf *conf, int num); 
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 void r5c_update_on_rdev_error(struct mddev *mddev);

#endif