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Btrfs: fix a crash when running balance and defrag concurrently

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Running balance and defrag concurrently can end up with a crash:

kernel BUG at fs/btrfs/relocation.c:4528!
RIP: 0010:[<ffffffffa01ac33b>]  [<ffffffffa01ac33b>] btrfs_reloc_cow_block+ 0x1eb/0x230 [btrfs]
Call Trace:
  [<ffffffffa01398c1>] ? update_ref_for_cow+0x241/0x380 [btrfs]
  [<ffffffffa0180bad>] ? copy_extent_buffer+0xad/0x110 [btrfs]
  [<ffffffffa0139da1>] __btrfs_cow_block+0x3a1/0x520 [btrfs]
  [<ffffffffa013a0b6>] btrfs_cow_block+0x116/0x1b0 [btrfs]
  [<ffffffffa013ddad>] btrfs_search_slot+0x43d/0x970 [btrfs]
  [<ffffffffa0153c57>] btrfs_lookup_file_extent+0x37/0x40 [btrfs]
  [<ffffffffa0172a5e>] __btrfs_drop_extents+0x11e/0xae0 [btrfs]
  [<ffffffffa013b3fd>] ? generic_bin_search.constprop.39+0x8d/0x1a0 [btrfs]
  [<ffffffff8117d14a>] ? kmem_cache_alloc+0x1da/0x200
  [<ffffffffa0138e7a>] ? btrfs_alloc_path+0x1a/0x20 [btrfs]
  [<ffffffffa0173ef0>] btrfs_drop_extents+0x60/0x90 [btrfs]
  [<ffffffffa016b24d>] relink_extent_backref+0x2ed/0x780 [btrfs]
  [<ffffffffa0162fe0>] ? btrfs_submit_bio_hook+0x1e0/0x1e0 [btrfs]
  [<ffffffffa01b8ed7>] ? iterate_inodes_from_logical+0x87/0xa0 [btrfs]
  [<ffffffffa016b909>] btrfs_finish_ordered_io+0x229/0xac0 [btrfs]
  [<ffffffffa016c3b5>] finish_ordered_fn+0x15/0x20 [btrfs]
  [<ffffffffa018cbe5>] worker_loop+0x125/0x4e0 [btrfs]
  [<ffffffffa018cac0>] ? btrfs_queue_worker+0x300/0x300 [btrfs]
  [<ffffffff81075ea0>] kthread+0xc0/0xd0
  [<ffffffff81075de0>] ? insert_kthread_work+0x40/0x40
  [<ffffffff8164796c>] ret_from_fork+0x7c/0xb0
  [<ffffffff81075de0>] ? insert_kthread_work+0x40/0x40
----------------------------------------------------------------------

It turns out to be that balance operation will bump root's @last_snapshot,
which enables snapshot-aware defrag path, and backref walking stuff will
find data reloc tree as refs' parent, and hit the BUG_ON() during COW.

As data reloc tree's data is just for relocation purpose, and will be deleted right
after relocation is done, it's unnecessary to walk those refs belonged to data reloc
tree, it'd be better to skip them.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
This commit is contained in:
Liu Bo 2013-10-30 13:25:24 +08:00 committed by Chris Mason
parent 6f519564d7
commit 48ec47364b
1 changed files with 3 additions and 0 deletions
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3
fs/btrfs/backref.c
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@ -185,6 +185,9 @@ static int __add_prelim_ref(struct list_head *head, u64 root_id,
{
struct __prelim_ref *ref;
if (root_id == BTRFS_DATA_RELOC_TREE_OBJECTID)
return 0;
ref = kmem_cache_alloc(btrfs_prelim_ref_cache, gfp_mask);
if (!ref)
return -ENOMEM;