| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.14 104/110] btrfs: fix lockdep warning with reclaim lock inversion | Date | Sat, 28 Jun 2014 10:47:41 -0700 |
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3.14-stable review patch. If anyone has any objections, please let me know.
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From: Jeff Mahoney <jeffm@suse.com>
commit ed55b6ac077fe7f9c6490ff55172c4b563562d7c upstream.
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: [<ffffffffa018baea>] __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); <Interrupt> lock(&delayed_node->mutex);
*** DEADLOCK *** 2 locks held by kswapd0/169: #0: (shrinker_rwsem){++++..}, at: [<ffffffff81159e8a>] shrink_slab+0x3a/0x160 #1: (&type->s_umount_key#27){++++..}, at: [<ffffffff811bac6f>] grab_super_passive+0x3f/0x90
Signed-off-by: Jeff Mahoney <jeffm@suse.com> Signed-off-by: Chris Mason <clm@fb.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- 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 @@ -8344,9 +8344,15 @@ 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; @@ -8358,8 +8364,6 @@ 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 *
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