diff options
author | Filipe Manana <fdmanana@suse.com> | 2018-10-24 10:13:03 +0100 |
---|---|---|
committer | David Sterba <dsterba@suse.com> | 2018-11-06 16:42:32 +0100 |
commit | 4222ea7100c0e37adace2790c8822758bbeee179 (patch) | |
tree | c10f267aaeaf99c03440f87177195f0e42f3e065 /fs/btrfs/ctree.h | |
parent | 7e17916b35797396f681a3270245fd29c1e4c250 (diff) |
Btrfs: fix deadlock on tree root leaf when finding free extent
When we are writing out a free space cache, during the transaction commit
phase, we can end up in a deadlock which results in a stack trace like the
following:
schedule+0x28/0x80
btrfs_tree_read_lock+0x8e/0x120 [btrfs]
? finish_wait+0x80/0x80
btrfs_read_lock_root_node+0x2f/0x40 [btrfs]
btrfs_search_slot+0xf6/0x9f0 [btrfs]
? evict_refill_and_join+0xd0/0xd0 [btrfs]
? inode_insert5+0x119/0x190
btrfs_lookup_inode+0x3a/0xc0 [btrfs]
? kmem_cache_alloc+0x166/0x1d0
btrfs_iget+0x113/0x690 [btrfs]
__lookup_free_space_inode+0xd8/0x150 [btrfs]
lookup_free_space_inode+0x5b/0xb0 [btrfs]
load_free_space_cache+0x7c/0x170 [btrfs]
? cache_block_group+0x72/0x3b0 [btrfs]
cache_block_group+0x1b3/0x3b0 [btrfs]
? finish_wait+0x80/0x80
find_free_extent+0x799/0x1010 [btrfs]
btrfs_reserve_extent+0x9b/0x180 [btrfs]
btrfs_alloc_tree_block+0x1b3/0x4f0 [btrfs]
__btrfs_cow_block+0x11d/0x500 [btrfs]
btrfs_cow_block+0xdc/0x180 [btrfs]
btrfs_search_slot+0x3bd/0x9f0 [btrfs]
btrfs_lookup_inode+0x3a/0xc0 [btrfs]
? kmem_cache_alloc+0x166/0x1d0
btrfs_update_inode_item+0x46/0x100 [btrfs]
cache_save_setup+0xe4/0x3a0 [btrfs]
btrfs_start_dirty_block_groups+0x1be/0x480 [btrfs]
btrfs_commit_transaction+0xcb/0x8b0 [btrfs]
At cache_save_setup() we need to update the inode item of a block group's
cache which is located in the tree root (fs_info->tree_root), which means
that it may result in COWing a leaf from that tree. If that happens we
need to find a free metadata extent and while looking for one, if we find
a block group which was not cached yet we attempt to load its cache by
calling cache_block_group(). However this function will try to load the
inode of the free space cache, which requires finding the matching inode
item in the tree root - if that inode item is located in the same leaf as
the inode item of the space cache we are updating at cache_save_setup(),
we end up in a deadlock, since we try to obtain a read lock on the same
extent buffer that we previously write locked.
So fix this by using the tree root's commit root when searching for a
block group's free space cache inode item when we are attempting to load
a free space cache. This is safe since block groups once loaded stay in
memory forever, as well as their caches, so after they are first loaded
we will never need to read their inode items again. For new block groups,
once they are created they get their ->cached field set to
BTRFS_CACHE_FINISHED meaning we will not need to read their inode item.
Reported-by: Andrew Nelson <andrew.s.nelson@gmail.com>
Link: https://lore.kernel.org/linux-btrfs/CAPTELenq9x5KOWuQ+fa7h1r3nsJG8vyiTH8+ifjURc_duHh2Wg@mail.gmail.com/
Fixes: 9d66e233c704 ("Btrfs: load free space cache if it exists")
Tested-by: Andrew Nelson <andrew.s.nelson@gmail.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/ctree.h')
-rw-r--r-- | fs/btrfs/ctree.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index 68ca41dbbef3..f7f955109d8b 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -3163,6 +3163,9 @@ void btrfs_destroy_inode(struct inode *inode); int btrfs_drop_inode(struct inode *inode); int __init btrfs_init_cachep(void); void __cold btrfs_destroy_cachep(void); +struct inode *btrfs_iget_path(struct super_block *s, struct btrfs_key *location, + struct btrfs_root *root, int *new, + struct btrfs_path *path); struct inode *btrfs_iget(struct super_block *s, struct btrfs_key *location, struct btrfs_root *root, int *was_new); struct extent_map *btrfs_get_extent(struct btrfs_inode *inode, |