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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 <jeffm@suse.com>
X-Patchwork-Id: 3894781
Message-Id: <5333184E.3090609@suse.com>
To: linux-btrfs <linux-btrfs@vger.kernel.org>
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: [<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>
---
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 *
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