Btrfs: fix regression running delayed references when using qgroups

In the kernel 4.2 merge window we had a big changes to the implementation
of delayed references and qgroups which made the no_quota field of delayed
references not used anymore. More specifically the no_quota field is not
used anymore as of:

  commit 0ed4792af0e8 ("btrfs: qgroup: Switch to new extent-oriented qgroup mechanism.")

Leaving the no_quota field actually prevents delayed references from
getting merged, which in turn cause the following BUG_ON(), at
fs/btrfs/extent-tree.c, to be hit when qgroups are enabled:

  static int run_delayed_tree_ref(...)
  {
     (...)
     BUG_ON(node->ref_mod != 1);
     (...)
  }

This happens on a scenario like the following:

  1) Ref1 bytenr X, action = BTRFS_ADD_DELAYED_REF, no_quota = 1, added.

  2) Ref2 bytenr X, action = BTRFS_DROP_DELAYED_REF, no_quota = 0, added.
     It's not merged with Ref1 because Ref1->no_quota != Ref2->no_quota.

  3) Ref3 bytenr X, action = BTRFS_ADD_DELAYED_REF, no_quota = 1, added.
     It's not merged with the reference at the tail of the list of refs
     for bytenr X because the reference at the tail, Ref2 is incompatible
     due to Ref2->no_quota != Ref3->no_quota.

  4) Ref4 bytenr X, action = BTRFS_DROP_DELAYED_REF, no_quota = 0, added.
     It's not merged with the reference at the tail of the list of refs
     for bytenr X because the reference at the tail, Ref3 is incompatible
     due to Ref3->no_quota != Ref4->no_quota.

  5) We run delayed references, trigger merging of delayed references,
     through __btrfs_run_delayed_refs() -> btrfs_merge_delayed_refs().

  6) Ref1 and Ref3 are merged as Ref1->no_quota = Ref3->no_quota and
     all other conditions are satisfied too. So Ref1 gets a ref_mod
     value of 2.

  7) Ref2 and Ref4 are merged as Ref2->no_quota = Ref4->no_quota and
     all other conditions are satisfied too. So Ref2 gets a ref_mod
     value of 2.

  8) Ref1 and Ref2 aren't merged, because they have different values
     for their no_quota field.

  9) Delayed reference Ref1 is picked for running (select_delayed_ref()
     always prefers references with an action == BTRFS_ADD_DELAYED_REF).
     So run_delayed_tree_ref() is called for Ref1 which triggers the
     BUG_ON because Ref1->red_mod != 1 (equals 2).

So fix this by removing the no_quota field, as it's not used anymore as
of commit 0ed4792af0e8 ("btrfs: qgroup: Switch to new extent-oriented
qgroup mechanism.").

The use of no_quota was also buggy in at least two places:

1) At delayed-refs.c:btrfs_add_delayed_tree_ref() - we were setting
   no_quota to 0 instead of 1 when the following condition was true:
   is_fstree(ref_root) || !fs_info->quota_enabled

2) At extent-tree.c:__btrfs_inc_extent_ref() - we were attempting to
   reset a node's no_quota when the condition "!is_fstree(root_objectid)
   || !root->fs_info->quota_enabled" was true but we did it only in
   an unused local stack variable, that is, we never reset the no_quota
   value in the node itself.

This fixes the remainder of problems several people have been having when
running delayed references, mostly while a balance is running in parallel,
on a 4.2+ kernel.

Very special thanks to Stéphane Lesimple for helping debugging this issue
and testing this fix on his multi terabyte filesystem (which took more
than one day to balance alone, plus fsck, etc).

Also, this fixes deadlock issue when using the clone ioctl with qgroups
enabled, as reported by Elias Probst in the mailing list. The deadlock
happens because after calling btrfs_insert_empty_item we have our path
holding a write lock on a leaf of the fs/subvol tree and then before
releasing the path we called check_ref() which did backref walking, when
qgroups are enabled, and tried to read lock the same leaf. The trace for
this case is the following:

  INFO: task systemd-nspawn:6095 blocked for more than 120 seconds.
  (...)
  Call Trace:
    [<ffffffff86999201>] schedule+0x74/0x83
    [<ffffffff863ef64c>] btrfs_tree_read_lock+0xc0/0xea
    [<ffffffff86137ed7>] ? wait_woken+0x74/0x74
    [<ffffffff8639f0a7>] btrfs_search_old_slot+0x51a/0x810
    [<ffffffff863a129b>] btrfs_next_old_leaf+0xdf/0x3ce
    [<ffffffff86413a00>] ? ulist_add_merge+0x1b/0x127
    [<ffffffff86411688>] __resolve_indirect_refs+0x62a/0x667
    [<ffffffff863ef546>] ? btrfs_clear_lock_blocking_rw+0x78/0xbe
    [<ffffffff864122d3>] find_parent_nodes+0xaf3/0xfc6
    [<ffffffff86412838>] __btrfs_find_all_roots+0x92/0xf0
    [<ffffffff864128f2>] btrfs_find_all_roots+0x45/0x65
    [<ffffffff8639a75b>] ? btrfs_get_tree_mod_seq+0x2b/0x88
    [<ffffffff863e852e>] check_ref+0x64/0xc4
    [<ffffffff863e9e01>] btrfs_clone+0x66e/0xb5d
    [<ffffffff863ea77f>] btrfs_ioctl_clone+0x48f/0x5bb
    [<ffffffff86048a68>] ? native_sched_clock+0x28/0x77
    [<ffffffff863ed9b0>] btrfs_ioctl+0xabc/0x25cb
  (...)

The problem goes away by eleminating check_ref(), which no longer is
needed as its purpose was to get a value for the no_quota field of
a delayed reference (this patch removes the no_quota field as mentioned
earlier).

Reported-by: Stéphane Lesimple <stephane_btrfs@lesimple.fr>
Tested-by: Stéphane Lesimple <stephane_btrfs@lesimple.fr>
Reported-by: Elias Probst <mail@eliasprobst.eu>
Reported-by: Peter Becker <floyd.net@gmail.com>
Reported-by: Malte Schröder <malte@tnxip.de>
Reported-by: Derek Dongray <derek@valedon.co.uk>
Reported-by: Erkki Seppala <flux-btrfs@inside.org>
Cc: stable@vger.kernel.org  # 4.2+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Qu Wenruo <quwenruo@cn.fujitsu.com>

1 files changed, 16 insertions, 29 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index c0f30f5d8a41..c1f8c7e27a6d 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -95,8 +95,7 @@ static int alloc_reserved_tree_block(struct btrfs_trans_handle *trans,
 				     struct btrfs_root *root,
 				     u64 parent, u64 root_objectid,
 				     u64 flags, struct btrfs_disk_key *key,
-				     int level, struct btrfs_key *ins,
-				     int no_quota);
+				     int level, struct btrfs_key *ins);
 static int do_chunk_alloc(struct btrfs_trans_handle *trans,
 			  struct btrfs_root *extent_root, u64 flags,
 			  int force);
@@ -2073,8 +2072,7 @@ int btrfs_discard_extent(struct btrfs_root *root, u64 bytenr,
 int btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
 			 struct btrfs_root *root,
 			 u64 bytenr, u64 num_bytes, u64 parent,
-			 u64 root_objectid, u64 owner, u64 offset,
-			 int no_quota)
+			 u64 root_objectid, u64 owner, u64 offset)
 {
 	int ret;
 	struct btrfs_fs_info *fs_info = root->fs_info;
@@ -2086,12 +2084,12 @@ int btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
 		ret = btrfs_add_delayed_tree_ref(fs_info, trans, bytenr,
 					num_bytes,
 					parent, root_objectid, (int)owner,
-					BTRFS_ADD_DELAYED_REF, NULL, no_quota);
+					BTRFS_ADD_DELAYED_REF, NULL);
 	} else {
 		ret = btrfs_add_delayed_data_ref(fs_info, trans, bytenr,
 					num_bytes,
 					parent, root_objectid, owner, offset,
-					BTRFS_ADD_DELAYED_REF, NULL, no_quota);
+					BTRFS_ADD_DELAYED_REF, NULL);
 	}
 	return ret;
 }
@@ -2112,15 +2110,11 @@ static int __btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
 	u64 num_bytes = node->num_bytes;
 	u64 refs;
 	int ret;
-	int no_quota = node->no_quota;
 
 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;
 
-	if (!is_fstree(root_objectid) || !root->fs_info->quota_enabled)
-		no_quota = 1;
-
 	path->reada = 1;
 	path->leave_spinning = 1;
 	/* this will setup the path even if it fails to insert the back ref */
@@ -2355,8 +2349,7 @@ static int run_delayed_tree_ref(struct btrfs_trans_handle *trans,
 						parent, ref_root,
 						extent_op->flags_to_set,
 						&extent_op->key,
-						ref->level, &ins,
-						node->no_quota);
+						ref->level, &ins);
 	} else if (node->action == BTRFS_ADD_DELAYED_REF) {
 		ret = __btrfs_inc_extent_ref(trans, root, node,
 					     parent, ref_root,
@@ -3192,7 +3185,7 @@ static int __btrfs_mod_ref(struct btrfs_trans_handle *trans,
 	int level;
 	int ret = 0;
 	int (*process_func)(struct btrfs_trans_handle *, struct btrfs_root *,
-			    u64, u64, u64, u64, u64, u64, int);
+			    u64, u64, u64, u64, u64, u64);
 
 
 	if (btrfs_test_is_dummy_root(root))
@@ -3233,15 +3226,14 @@ static int __btrfs_mod_ref(struct btrfs_trans_handle *trans,
 			key.offset -= btrfs_file_extent_offset(buf, fi);
 			ret = process_func(trans, root, bytenr, num_bytes,
 					   parent, ref_root, key.objectid,
-					   key.offset, 1);
+					   key.offset);
 			if (ret)
 				goto fail;
 		} else {
 			bytenr = btrfs_node_blockptr(buf, i);
 			num_bytes = root->nodesize;
 			ret = process_func(trans, root, bytenr, num_bytes,
-					   parent, ref_root, level - 1, 0,
-					   1);
+					   parent, ref_root, level - 1, 0);
 			if (ret)
 				goto fail;
 		}
@@ -6431,7 +6423,6 @@ static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
 	int extent_slot = 0;
 	int found_extent = 0;
 	int num_to_del = 1;
-	int no_quota = node->no_quota;
 	u32 item_size;
 	u64 refs;
 	u64 bytenr = node->bytenr;
@@ -6440,9 +6431,6 @@ static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
 	bool skinny_metadata = btrfs_fs_incompat(root->fs_info,
 						 SKINNY_METADATA);
 
-	if (!info->quota_enabled || !is_fstree(root_objectid))
-		no_quota = 1;
-
 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;
@@ -6768,7 +6756,7 @@ void btrfs_free_tree_block(struct btrfs_trans_handle *trans,
 					buf->start, buf->len,
 					parent, root->root_key.objectid,
 					btrfs_header_level(buf),
-					BTRFS_DROP_DELAYED_REF, NULL, 0);
+					BTRFS_DROP_DELAYED_REF, NULL);
 		BUG_ON(ret); /* -ENOMEM */
 	}
 
@@ -6816,7 +6804,7 @@ out:
 /* Can return -ENOMEM */
 int btrfs_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 		      u64 bytenr, u64 num_bytes, u64 parent, u64 root_objectid,
-		      u64 owner, u64 offset, int no_quota)
+		      u64 owner, u64 offset)
 {
 	int ret;
 	struct btrfs_fs_info *fs_info = root->fs_info;
@@ -6839,13 +6827,13 @@ int btrfs_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 		ret = btrfs_add_delayed_tree_ref(fs_info, trans, bytenr,
 					num_bytes,
 					parent, root_objectid, (int)owner,
-					BTRFS_DROP_DELAYED_REF, NULL, no_quota);
+					BTRFS_DROP_DELAYED_REF, NULL);
 	} else {
 		ret = btrfs_add_delayed_data_ref(fs_info, trans, bytenr,
 						num_bytes,
 						parent, root_objectid, owner,
 						offset, BTRFS_DROP_DELAYED_REF,
-						NULL, no_quota);
+						NULL);
 	}
 	return ret;
 }
@@ -7690,8 +7678,7 @@ static int alloc_reserved_tree_block(struct btrfs_trans_handle *trans,
 				     struct btrfs_root *root,
 				     u64 parent, u64 root_objectid,
 				     u64 flags, struct btrfs_disk_key *key,
-				     int level, struct btrfs_key *ins,
-				     int no_quota)
+				     int level, struct btrfs_key *ins)
 {
 	int ret;
 	struct btrfs_fs_info *fs_info = root->fs_info;
@@ -7781,7 +7768,7 @@ int btrfs_alloc_reserved_file_extent(struct btrfs_trans_handle *trans,
 	ret = btrfs_add_delayed_data_ref(root->fs_info, trans, ins->objectid,
 					 ins->offset, 0,
 					 root_objectid, owner, offset,
-					 BTRFS_ADD_DELAYED_EXTENT, NULL, 0);
+					 BTRFS_ADD_DELAYED_EXTENT, NULL);
 	return ret;
 }
 
@@ -7995,7 +7982,7 @@ struct extent_buffer *btrfs_alloc_tree_block(struct btrfs_trans_handle *trans,
 						 ins.objectid, ins.offset,
 						 parent, root_objectid, level,
 						 BTRFS_ADD_DELAYED_EXTENT,
-						 extent_op, 0);
+						 extent_op);
 		if (ret)
 			goto out_free_delayed;
 	}
@@ -8544,7 +8531,7 @@ skip:
 			}
 		}
 		ret = btrfs_free_extent(trans, root, bytenr, blocksize, parent,
-				root->root_key.objectid, level - 1, 0, 0);
+				root->root_key.objectid, level - 1, 0);
 		BUG_ON(ret); /* -ENOMEM */
 	}
 	btrfs_tree_unlock(next);