From patchwork Wed Mar 26 18:11:26 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: btrfs: fix lockdep warning with reclaim lock inversion From: Jeff Mahoney X-Patchwork-Id: 3894781 Message-Id: <5333184E.3090609@suse.com> To: linux-btrfs Date: Wed, 26 Mar 2014 14:11:26 -0400 When encountering memory pressure, testers have run into the following lockdep warning. It was caused by __link_block_group calling kobject_add with the groups_sem held. kobject_add calls kvasprintf with GFP_KERNEL, which gets us into reclaim context. The kobject doesn't actually need to be added under the lock -- it just needs to ensure that it's only added for the first block group to be linked. ========================================================= [ INFO: possible irq lock inversion dependency detected ] 3.14.0-rc8-default #1 Not tainted --------------------------------------------------------- kswapd0/169 just changed the state of lock: (&delayed_node->mutex){+.+.-.}, at: [] __btrfs_release_delayed_node+0x3a/0x200 [btrfs] but this lock took another, RECLAIM_FS-unsafe lock in the past: (&found->groups_sem){+++++.} and interrupts could create inverse lock ordering between them. other info that might help us debug this: Possible interrupt unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&found->groups_sem); local_irq_disable(); lock(&delayed_node->mutex); lock(&found->groups_sem); lock(&delayed_node->mutex); *** DEADLOCK *** 2 locks held by kswapd0/169: #0: (shrinker_rwsem){++++..}, at: [] shrink_slab+0x3a/0x160 #1: (&type->s_umount_key#27){++++..}, at: [] grab_super_passive+0x3f/0x90 Signed-off-by: Jeff Mahoney --- fs/btrfs/extent-tree.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -8343,9 +8343,15 @@ static void __link_block_group(struct bt struct btrfs_block_group_cache *cache) { int index = get_block_group_index(cache); + bool first = false; down_write(&space_info->groups_sem); - if (list_empty(&space_info->block_groups[index])) { + if (list_empty(&space_info->block_groups[index])) + first = true; + list_add_tail(&cache->list, &space_info->block_groups[index]); + up_write(&space_info->groups_sem); + + if (first) { struct kobject *kobj = &space_info->block_group_kobjs[index]; int ret; @@ -8357,8 +8363,6 @@ static void __link_block_group(struct bt kobject_put(&space_info->kobj); } } - list_add_tail(&cache->list, &space_info->block_groups[index]); - up_write(&space_info->groups_sem); } static struct btrfs_block_group_cache *