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Commit 6ab2a4b8 authored by Shaohua Li's avatar Shaohua Li
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RAID5: revert e9e4c377 to fix a livelock 



Revert commit
e9e4c377(md/raid5: per hash value and exclusive wait_for_stripe)

The problem is raid5_get_active_stripe waits on
conf->wait_for_stripe[hash]. Assume hash is 0. My test release stripes
in this order:
- release all stripes with hash 0
- raid5_get_active_stripe still sleeps since active_stripes >
  max_nr_stripes * 3 / 4
- release all stripes with hash other than 0. active_stripes becomes 0
- raid5_get_active_stripe still sleeps, since nobody wakes up
  wait_for_stripe[0]
The system live locks. The problem is active_stripes isn't a per-hash
count. Revert the patch makes the live lock go away.

Cc: stable@vger.kernel.org (v4.2+)
Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Cc: NeilBrown <neilb@suse.de>
Signed-off-by: default avatarShaohua Li <shli@fb.com>
parent 27a353c0

drivers/md/raid5.c

+8 −19
Original line number Diff line number Diff line
@@ -340,8 +340,7 @@ static void release_inactive_stripe_list(struct r5conf *conf, 
					 int hash)

{

	int size;

	unsigned long do_wakeup = 0;

	int i = 0;

	bool do_wakeup = false;

	unsigned long flags;



	if (hash == NR_STRIPE_HASH_LOCKS) {
@@ -362,19 +361,15 @@ static void release_inactive_stripe_list(struct r5conf *conf, 
			    !list_empty(list))

				atomic_dec(&conf->empty_inactive_list_nr);

			list_splice_tail_init(list, conf->inactive_list + hash);

			do_wakeup |= 1 << hash;

			do_wakeup = true;

			spin_unlock_irqrestore(conf->hash_locks + hash, flags);

		}

		size--;

		hash--;

	}



	for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++) {

		if (do_wakeup & (1 << i))

			wake_up(&conf->wait_for_stripe[i]);

	}



	if (do_wakeup) {

		wake_up(&conf->wait_for_stripe);

		if (atomic_read(&conf->active_stripes) == 0)

			wake_up(&conf->wait_for_quiescent);

		if (conf->retry_read_aligned)
@@ -687,15 +682,14 @@ raid5_get_active_stripe(struct r5conf *conf, sector_t sector, 
			if (!sh) {

				set_bit(R5_INACTIVE_BLOCKED,

					&conf->cache_state);

				wait_event_exclusive_cmd(

					conf->wait_for_stripe[hash],

				wait_event_lock_irq(

					conf->wait_for_stripe,

					!list_empty(conf->inactive_list + hash) &&

					(atomic_read(&conf->active_stripes)

					 < (conf->max_nr_stripes * 3 / 4)

					 || !test_bit(R5_INACTIVE_BLOCKED,

						      &conf->cache_state)),

					spin_unlock_irq(conf->hash_locks + hash),

					spin_lock_irq(conf->hash_locks + hash));

					*(conf->hash_locks + hash));

				clear_bit(R5_INACTIVE_BLOCKED,

					  &conf->cache_state);

			} else {
@@ -720,9 +714,6 @@ raid5_get_active_stripe(struct r5conf *conf, sector_t sector, 
		}

	} while (sh == NULL);



	if (!list_empty(conf->inactive_list + hash))

		wake_up(&conf->wait_for_stripe[hash]);



	spin_unlock_irq(conf->hash_locks + hash);

	return sh;

}
@@ -2202,7 +2193,7 @@ static int resize_stripes(struct r5conf *conf, int newsize) 
	cnt = 0;

	list_for_each_entry(nsh, &newstripes, lru) {

		lock_device_hash_lock(conf, hash);

		wait_event_exclusive_cmd(conf->wait_for_stripe[hash],

		wait_event_cmd(conf->wait_for_stripe,

				    !list_empty(conf->inactive_list + hash),

				    unlock_device_hash_lock(conf, hash),

				    lock_device_hash_lock(conf, hash));
@@ -6521,9 +6512,7 @@ static struct r5conf *setup_conf(struct mddev *mddev) 
	seqcount_init(&conf->gen_lock);

	mutex_init(&conf->cache_size_mutex);

	init_waitqueue_head(&conf->wait_for_quiescent);

	for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++) {

		init_waitqueue_head(&conf->wait_for_stripe[i]);

	}

	init_waitqueue_head(&conf->wait_for_stripe);

	init_waitqueue_head(&conf->wait_for_overlap);

	INIT_LIST_HEAD(&conf->handle_list);

	INIT_LIST_HEAD(&conf->hold_list);

drivers/md/raid5.h

+1 −1
Original line number Diff line number Diff line
@@ -524,7 +524,7 @@ struct r5conf { 
	atomic_t		empty_inactive_list_nr;

	struct llist_head	released_stripes;

	wait_queue_head_t	wait_for_quiescent;

	wait_queue_head_t	wait_for_stripe[NR_STRIPE_HASH_LOCKS];

	wait_queue_head_t	wait_for_stripe;

	wait_queue_head_t	wait_for_overlap;

	unsigned long		cache_state;

#define R5_INACTIVE_BLOCKED	1	/* release of inactive stripes blocked,