RAID5: revert e9e4c377e2f563 to fix a livelock

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>

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index b628cd525b320306e8a0944ea422afdaec827033..c25f2fb2e567c958724047440d976725d185a852 100644 (file)
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -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);

diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index ae6068deefdfb0b69c41cbbae9d0ee5d89b3b381..517d4b68a1befcad9e4b383c0ed077133d25b3b3 100644 (file)
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -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,