80 lines
2.9 KiB
Diff
80 lines
2.9 KiB
Diff
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From patchwork Wed Mar 26 18:11:26 2014
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Content-Type: text/plain; charset="utf-8"
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MIME-Version: 1.0
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Content-Transfer-Encoding: 7bit
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Subject: btrfs: fix lockdep warning with reclaim lock inversion
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From: Jeff Mahoney <jeffm@suse.com>
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X-Patchwork-Id: 3894781
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Message-Id: <5333184E.3090609@suse.com>
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To: linux-btrfs <linux-btrfs@vger.kernel.org>
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Date: Wed, 26 Mar 2014 14:11:26 -0400
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When encountering memory pressure, testers have run into the following
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lockdep warning. It was caused by __link_block_group calling kobject_add
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with the groups_sem held. kobject_add calls kvasprintf with GFP_KERNEL,
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which gets us into reclaim context. The kobject doesn't actually need
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to be added under the lock -- it just needs to ensure that it's only
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added for the first block group to be linked.
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=========================================================
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[ INFO: possible irq lock inversion dependency detected ]
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3.14.0-rc8-default #1 Not tainted
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---------------------------------------------------------
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kswapd0/169 just changed the state of lock:
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(&delayed_node->mutex){+.+.-.}, at: [<ffffffffa018baea>] __btrfs_release_delayed_node+0x3a/0x200 [btrfs]
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but this lock took another, RECLAIM_FS-unsafe lock in the past:
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(&found->groups_sem){+++++.}
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and interrupts could create inverse lock ordering between them.
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other info that might help us debug this:
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Possible interrupt unsafe locking scenario:
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CPU0 CPU1
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---- ----
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lock(&found->groups_sem);
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local_irq_disable();
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lock(&delayed_node->mutex);
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lock(&found->groups_sem);
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<Interrupt>
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lock(&delayed_node->mutex);
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*** DEADLOCK ***
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2 locks held by kswapd0/169:
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#0: (shrinker_rwsem){++++..}, at: [<ffffffff81159e8a>] shrink_slab+0x3a/0x160
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#1: (&type->s_umount_key#27){++++..}, at: [<ffffffff811bac6f>] grab_super_passive+0x3f/0x90
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Signed-off-by: Jeff Mahoney <jeffm@suse.com>
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---
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fs/btrfs/extent-tree.c | 10 +++++++---
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1 file changed, 7 insertions(+), 3 deletions(-)
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--- a/fs/btrfs/extent-tree.c
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+++ b/fs/btrfs/extent-tree.c
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@@ -8343,9 +8343,15 @@ static void __link_block_group(struct bt
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struct btrfs_block_group_cache *cache)
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{
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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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- 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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+
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+ if (first) {
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struct kobject *kobj = &space_info->block_group_kobjs[index];
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int ret;
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@@ -8357,8 +8363,6 @@ static void __link_block_group(struct bt
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kobject_put(&space_info->kobj);
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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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static struct btrfs_block_group_cache *
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