diff options
author | Josef Bacik <josef@toxicpanda.com> | 2020-10-19 23:02:31 +0300 |
---|---|---|
committer | David Sterba <dsterba@suse.com> | 2020-10-26 17:04:57 +0300 |
commit | 49d11bead7d596e031fbd34051d8765587cd645b (patch) | |
tree | c8d71e6da6dfbbd3c28c0f41ae0a2faa2adbebee /fs/btrfs/disk-io.c | |
parent | 5223cc60b40ae525ae6c94e98824129f1a5b4ae5 (diff) | |
download | linux-49d11bead7d596e031fbd34051d8765587cd645b.tar.xz |
btrfs: add a helper to read the tree_root commit root for backref lookup
I got the following lockdep splat with tree locks converted to rwsem
patches on btrfs/104:
======================================================
WARNING: possible circular locking dependency detected
5.9.0+ #102 Not tainted
------------------------------------------------------
btrfs-cleaner/903 is trying to acquire lock:
ffff8e7fab6ffe30 (btrfs-root-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x32/0x170
but task is already holding lock:
ffff8e7fab628a88 (&fs_info->commit_root_sem){++++}-{3:3}, at: btrfs_find_all_roots+0x41/0x80
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #3 (&fs_info->commit_root_sem){++++}-{3:3}:
down_read+0x40/0x130
caching_thread+0x53/0x5a0
btrfs_work_helper+0xfa/0x520
process_one_work+0x238/0x540
worker_thread+0x55/0x3c0
kthread+0x13a/0x150
ret_from_fork+0x1f/0x30
-> #2 (&caching_ctl->mutex){+.+.}-{3:3}:
__mutex_lock+0x7e/0x7b0
btrfs_cache_block_group+0x1e0/0x510
find_free_extent+0xb6e/0x12f0
btrfs_reserve_extent+0xb3/0x1b0
btrfs_alloc_tree_block+0xb1/0x330
alloc_tree_block_no_bg_flush+0x4f/0x60
__btrfs_cow_block+0x11d/0x580
btrfs_cow_block+0x10c/0x220
commit_cowonly_roots+0x47/0x2e0
btrfs_commit_transaction+0x595/0xbd0
sync_filesystem+0x74/0x90
generic_shutdown_super+0x22/0x100
kill_anon_super+0x14/0x30
btrfs_kill_super+0x12/0x20
deactivate_locked_super+0x36/0xa0
cleanup_mnt+0x12d/0x190
task_work_run+0x5c/0xa0
exit_to_user_mode_prepare+0x1df/0x200
syscall_exit_to_user_mode+0x54/0x280
entry_SYSCALL_64_after_hwframe+0x44/0xa9
-> #1 (&space_info->groups_sem){++++}-{3:3}:
down_read+0x40/0x130
find_free_extent+0x2ed/0x12f0
btrfs_reserve_extent+0xb3/0x1b0
btrfs_alloc_tree_block+0xb1/0x330
alloc_tree_block_no_bg_flush+0x4f/0x60
__btrfs_cow_block+0x11d/0x580
btrfs_cow_block+0x10c/0x220
commit_cowonly_roots+0x47/0x2e0
btrfs_commit_transaction+0x595/0xbd0
sync_filesystem+0x74/0x90
generic_shutdown_super+0x22/0x100
kill_anon_super+0x14/0x30
btrfs_kill_super+0x12/0x20
deactivate_locked_super+0x36/0xa0
cleanup_mnt+0x12d/0x190
task_work_run+0x5c/0xa0
exit_to_user_mode_prepare+0x1df/0x200
syscall_exit_to_user_mode+0x54/0x280
entry_SYSCALL_64_after_hwframe+0x44/0xa9
-> #0 (btrfs-root-00){++++}-{3:3}:
__lock_acquire+0x1167/0x2150
lock_acquire+0xb9/0x3d0
down_read_nested+0x43/0x130
__btrfs_tree_read_lock+0x32/0x170
__btrfs_read_lock_root_node+0x3a/0x50
btrfs_search_slot+0x614/0x9d0
btrfs_find_root+0x35/0x1b0
btrfs_read_tree_root+0x61/0x120
btrfs_get_root_ref+0x14b/0x600
find_parent_nodes+0x3e6/0x1b30
btrfs_find_all_roots_safe+0xb4/0x130
btrfs_find_all_roots+0x60/0x80
btrfs_qgroup_trace_extent_post+0x27/0x40
btrfs_add_delayed_data_ref+0x3fd/0x460
btrfs_free_extent+0x42/0x100
__btrfs_mod_ref+0x1d7/0x2f0
walk_up_proc+0x11c/0x400
walk_up_tree+0xf0/0x180
btrfs_drop_snapshot+0x1c7/0x780
btrfs_clean_one_deleted_snapshot+0xfb/0x110
cleaner_kthread+0xd4/0x140
kthread+0x13a/0x150
ret_from_fork+0x1f/0x30
other info that might help us debug this:
Chain exists of:
btrfs-root-00 --> &caching_ctl->mutex --> &fs_info->commit_root_sem
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&fs_info->commit_root_sem);
lock(&caching_ctl->mutex);
lock(&fs_info->commit_root_sem);
lock(btrfs-root-00);
*** DEADLOCK ***
3 locks held by btrfs-cleaner/903:
#0: ffff8e7fab628838 (&fs_info->cleaner_mutex){+.+.}-{3:3}, at: cleaner_kthread+0x6e/0x140
#1: ffff8e7faadac640 (sb_internal){.+.+}-{0:0}, at: start_transaction+0x40b/0x5c0
#2: ffff8e7fab628a88 (&fs_info->commit_root_sem){++++}-{3:3}, at: btrfs_find_all_roots+0x41/0x80
stack backtrace:
CPU: 0 PID: 903 Comm: btrfs-cleaner Not tainted 5.9.0+ #102
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-2.fc32 04/01/2014
Call Trace:
dump_stack+0x8b/0xb0
check_noncircular+0xcf/0xf0
__lock_acquire+0x1167/0x2150
? __bfs+0x42/0x210
lock_acquire+0xb9/0x3d0
? __btrfs_tree_read_lock+0x32/0x170
down_read_nested+0x43/0x130
? __btrfs_tree_read_lock+0x32/0x170
__btrfs_tree_read_lock+0x32/0x170
__btrfs_read_lock_root_node+0x3a/0x50
btrfs_search_slot+0x614/0x9d0
? find_held_lock+0x2b/0x80
btrfs_find_root+0x35/0x1b0
? do_raw_spin_unlock+0x4b/0xa0
btrfs_read_tree_root+0x61/0x120
btrfs_get_root_ref+0x14b/0x600
find_parent_nodes+0x3e6/0x1b30
btrfs_find_all_roots_safe+0xb4/0x130
btrfs_find_all_roots+0x60/0x80
btrfs_qgroup_trace_extent_post+0x27/0x40
btrfs_add_delayed_data_ref+0x3fd/0x460
btrfs_free_extent+0x42/0x100
__btrfs_mod_ref+0x1d7/0x2f0
walk_up_proc+0x11c/0x400
walk_up_tree+0xf0/0x180
btrfs_drop_snapshot+0x1c7/0x780
? btrfs_clean_one_deleted_snapshot+0x73/0x110
btrfs_clean_one_deleted_snapshot+0xfb/0x110
cleaner_kthread+0xd4/0x140
? btrfs_alloc_root+0x50/0x50
kthread+0x13a/0x150
? kthread_create_worker_on_cpu+0x40/0x40
ret_from_fork+0x1f/0x30
BTRFS info (device sdb): disk space caching is enabled
BTRFS info (device sdb): has skinny extents
This happens because qgroups does a backref lookup when we create a
delayed ref. From here it may have to look up a root from an indirect
ref, which does a normal lookup on the tree_root, which takes the read
lock on the tree_root nodes.
To fix this we need to add a variant for looking up roots that searches
the commit root of the tree_root. Then when we do the backref search
using the commit root we are sure to not take any locks on the tree_root
nodes. This gets rid of the lockdep splat when running btrfs/104.
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/disk-io.c')
-rw-r--r-- | fs/btrfs/disk-io.c | 139 |
1 files changed, 99 insertions, 40 deletions
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index 764001609a15..278001a49d2e 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -1281,32 +1281,26 @@ int btrfs_add_log_tree(struct btrfs_trans_handle *trans, return 0; } -struct btrfs_root *btrfs_read_tree_root(struct btrfs_root *tree_root, - struct btrfs_key *key) +static struct btrfs_root *read_tree_root_path(struct btrfs_root *tree_root, + struct btrfs_path *path, + struct btrfs_key *key) { struct btrfs_root *root; struct btrfs_fs_info *fs_info = tree_root->fs_info; - struct btrfs_path *path; u64 generation; int ret; int level; - path = btrfs_alloc_path(); - if (!path) - return ERR_PTR(-ENOMEM); - root = btrfs_alloc_root(fs_info, key->objectid, GFP_NOFS); - if (!root) { - ret = -ENOMEM; - goto alloc_fail; - } + if (!root) + return ERR_PTR(-ENOMEM); ret = btrfs_find_root(tree_root, key, path, &root->root_item, &root->root_key); if (ret) { if (ret > 0) ret = -ENOENT; - goto find_fail; + goto fail; } generation = btrfs_root_generation(&root->root_item); @@ -1317,21 +1311,31 @@ struct btrfs_root *btrfs_read_tree_root(struct btrfs_root *tree_root, if (IS_ERR(root->node)) { ret = PTR_ERR(root->node); root->node = NULL; - goto find_fail; + goto fail; } else if (!btrfs_buffer_uptodate(root->node, generation, 0)) { ret = -EIO; - goto find_fail; + goto fail; } root->commit_root = btrfs_root_node(root); -out: - btrfs_free_path(path); return root; - -find_fail: +fail: btrfs_put_root(root); -alloc_fail: - root = ERR_PTR(ret); - goto out; + return ERR_PTR(ret); +} + +struct btrfs_root *btrfs_read_tree_root(struct btrfs_root *tree_root, + struct btrfs_key *key) +{ + struct btrfs_root *root; + struct btrfs_path *path; + + path = btrfs_alloc_path(); + if (!path) + return ERR_PTR(-ENOMEM); + root = read_tree_root_path(tree_root, path, key); + btrfs_free_path(path); + + return root; } /* @@ -1419,6 +1423,31 @@ static struct btrfs_root *btrfs_lookup_fs_root(struct btrfs_fs_info *fs_info, return root; } +static struct btrfs_root *btrfs_get_global_root(struct btrfs_fs_info *fs_info, + u64 objectid) +{ + if (objectid == BTRFS_ROOT_TREE_OBJECTID) + return btrfs_grab_root(fs_info->tree_root); + if (objectid == BTRFS_EXTENT_TREE_OBJECTID) + return btrfs_grab_root(fs_info->extent_root); + if (objectid == BTRFS_CHUNK_TREE_OBJECTID) + return btrfs_grab_root(fs_info->chunk_root); + if (objectid == BTRFS_DEV_TREE_OBJECTID) + return btrfs_grab_root(fs_info->dev_root); + if (objectid == BTRFS_CSUM_TREE_OBJECTID) + return btrfs_grab_root(fs_info->csum_root); + if (objectid == BTRFS_QUOTA_TREE_OBJECTID) + return btrfs_grab_root(fs_info->quota_root) ? + fs_info->quota_root : ERR_PTR(-ENOENT); + if (objectid == BTRFS_UUID_TREE_OBJECTID) + return btrfs_grab_root(fs_info->uuid_root) ? + fs_info->uuid_root : ERR_PTR(-ENOENT); + if (objectid == BTRFS_FREE_SPACE_TREE_OBJECTID) + return btrfs_grab_root(fs_info->free_space_root) ? + fs_info->free_space_root : ERR_PTR(-ENOENT); + return NULL; +} + int btrfs_insert_fs_root(struct btrfs_fs_info *fs_info, struct btrfs_root *root) { @@ -1518,25 +1547,9 @@ static struct btrfs_root *btrfs_get_root_ref(struct btrfs_fs_info *fs_info, struct btrfs_key key; int ret; - if (objectid == BTRFS_ROOT_TREE_OBJECTID) - return btrfs_grab_root(fs_info->tree_root); - if (objectid == BTRFS_EXTENT_TREE_OBJECTID) - return btrfs_grab_root(fs_info->extent_root); - if (objectid == BTRFS_CHUNK_TREE_OBJECTID) - return btrfs_grab_root(fs_info->chunk_root); - if (objectid == BTRFS_DEV_TREE_OBJECTID) - return btrfs_grab_root(fs_info->dev_root); - if (objectid == BTRFS_CSUM_TREE_OBJECTID) - return btrfs_grab_root(fs_info->csum_root); - if (objectid == BTRFS_QUOTA_TREE_OBJECTID) - return btrfs_grab_root(fs_info->quota_root) ? - fs_info->quota_root : ERR_PTR(-ENOENT); - if (objectid == BTRFS_UUID_TREE_OBJECTID) - return btrfs_grab_root(fs_info->uuid_root) ? - fs_info->uuid_root : ERR_PTR(-ENOENT); - if (objectid == BTRFS_FREE_SPACE_TREE_OBJECTID) - return btrfs_grab_root(fs_info->free_space_root) ? - fs_info->free_space_root : ERR_PTR(-ENOENT); + root = btrfs_get_global_root(fs_info, objectid); + if (root) + return root; again: root = btrfs_lookup_fs_root(fs_info, objectid); if (root) { @@ -1622,6 +1635,52 @@ struct btrfs_root *btrfs_get_new_fs_root(struct btrfs_fs_info *fs_info, } /* + * btrfs_get_fs_root_commit_root - return a root for the given objectid + * @fs_info: the fs_info + * @objectid: the objectid we need to lookup + * + * This is exclusively used for backref walking, and exists specifically because + * of how qgroups does lookups. Qgroups will do a backref lookup at delayed ref + * creation time, which means we may have to read the tree_root in order to look + * up a fs root that is not in memory. If the root is not in memory we will + * read the tree root commit root and look up the fs root from there. This is a + * temporary root, it will not be inserted into the radix tree as it doesn't + * have the most uptodate information, it'll simply be discarded once the + * backref code is finished using the root. + */ +struct btrfs_root *btrfs_get_fs_root_commit_root(struct btrfs_fs_info *fs_info, + struct btrfs_path *path, + u64 objectid) +{ + struct btrfs_root *root; + struct btrfs_key key; + + ASSERT(path->search_commit_root && path->skip_locking); + + /* + * This can return -ENOENT if we ask for a root that doesn't exist, but + * since this is called via the backref walking code we won't be looking + * up a root that doesn't exist, unless there's corruption. So if root + * != NULL just return it. + */ + root = btrfs_get_global_root(fs_info, objectid); + if (root) + return root; + + root = btrfs_lookup_fs_root(fs_info, objectid); + if (root) + return root; + + key.objectid = objectid; + key.type = BTRFS_ROOT_ITEM_KEY; + key.offset = (u64)-1; + root = read_tree_root_path(fs_info->tree_root, path, &key); + btrfs_release_path(path); + + return root; +} + +/* * called by the kthread helper functions to finally call the bio end_io * functions. This is where read checksum verification actually happens */ |