This is a note to let you know that I've just added the patch titled RAID5: revert e9e4c377e2f563 to fix a livelock to the 4.5-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: raid5-revert-e9e4c377e2f563-to-fix-a-livelock.patch and it can be found in the queue-4.5 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 6ab2a4b806ae21b6c3e47c5ff1285ec06d505325 Mon Sep 17 00:00:00 2001 From: Shaohua Li <shli@xxxxxx> Date: Thu, 25 Feb 2016 16:24:42 -0800 Subject: RAID5: revert e9e4c377e2f563 to fix a livelock From: Shaohua Li <shli@xxxxxx> commit 6ab2a4b806ae21b6c3e47c5ff1285ec06d505325 upstream. 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: Yuanhan Liu <yuanhan.liu@xxxxxxxxxxxxxxx> Cc: NeilBrown <neilb@xxxxxxx> Signed-off-by: Shaohua Li <shli@xxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/md/raid5.c | 27 ++++++++------------------- drivers/md/raid5.h | 2 +- 2 files changed, 9 insertions(+), 20 deletions(-) --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -340,8 +340,7 @@ static void release_inactive_stripe_list 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 !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 *c 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 *c } } 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 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 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); --- 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, Patches currently in stable-queue which might be from shli@xxxxxx are queue-4.5/raid10-include-bio_end_io_list-in-nr_queued-to-prevent-freeze_array-hang.patch queue-4.5/md-multipath-don-t-hardcopy-bio-in-.make_request-path.patch queue-4.5/raid5-revert-e9e4c377e2f563-to-fix-a-livelock.patch queue-4.5/raid1-include-bio_end_io_list-in-nr_queued-to-prevent-freeze_array-hang.patch queue-4.5/raid5-check_reshape-shouldn-t-call-mddev_suspend.patch queue-4.5/md-raid5-compare-apples-to-apples-or-sectors-to-sectors.patch queue-4.5/md-raid5-preserve-stripe_preread_active-in-break_stripe_batch_list.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html