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RAID5: revert e9e4c377e2 to fix a livelock

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Revert commit
e9e4c377e2f563(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: Shaohua Li <shli@fb.com>
This commit is contained in:
Shaohua Li 2016-02-25 16:24:42 -08:00
parent 27a353c026
commit 6ab2a4b806
2 changed files with 9 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
drivers/md/raid5.c
View File

@ -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);

2
drivers/md/raid5.h
View File

@ -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,