btrfs: fix lockdep warning with reclaim lock inversion
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>
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@ -8337,9 +8337,15 @@ static void __link_block_group(struct btrfs_space_info *space_info,
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struct btrfs_block_group_cache *cache)
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struct btrfs_block_group_cache *cache)
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{
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{
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int index = get_block_group_index(cache);
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int index = get_block_group_index(cache);
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bool first = false;
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down_write(&space_info->groups_sem);
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down_write(&space_info->groups_sem);
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if (list_empty(&space_info->block_groups[index])) {
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if (list_empty(&space_info->block_groups[index]))
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first = true;
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list_add_tail(&cache->list, &space_info->block_groups[index]);
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up_write(&space_info->groups_sem);
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if (first) {
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struct kobject *kobj = &space_info->block_group_kobjs[index];
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struct kobject *kobj = &space_info->block_group_kobjs[index];
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int ret;
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int ret;
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@ -8351,8 +8357,6 @@ static void __link_block_group(struct btrfs_space_info *space_info,
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kobject_put(&space_info->kobj);
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kobject_put(&space_info->kobj);
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}
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}
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}
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}
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list_add_tail(&cache->list, &space_info->block_groups[index]);
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up_write(&space_info->groups_sem);
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}
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}
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static struct btrfs_block_group_cache *
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static struct btrfs_block_group_cache *
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