btrfs-progs/transaction.c
Qu Wenruo 2a8cec4b12 btrfs-progs: Exhaust delayed refs and dirty block groups to prevent delayed refs lost
[BUG]
Btrfs-progs sometimes fails to find certain extent backref when
committing transaction.
The most reliable way to reproduce it is fsck-test/013 on 64K page sized
system:

  [...]
  adding new data backref on 315859712 root 287 owner 292 offset 0 found 1
  btrfs unable to find ref byte nr 31850496 parent 0 root 2  owner 0 offset 0
  Failed to find [30867456, 168, 65536]

Also there are some github bug reports related to this problem.

[CAUSE]
Commit 909357e867 ("btrfs-progs: Wire up delayed refs") introduced
delayed refs in btrfs-progs.

However in that commit, delayed refs are not run at correct timing.
That commit calls btrfs_run_delayed_refs() before
btrfs_write_dirty_block_groups(), which needs to update
BLOCK_GROUP_ITEMs in extent tree, thus could cause new delayed refs.

This means each time we commit a transaction, we may screw up the extent
tree by dropping some pending delayed refs, like:

Transaction 711:
btrfs_commit_transaction()
|- btrfs_run_delayed_refs()
|  Now all delayed refs are written to extent tree
|
|- btrfs_write_dirty_block_groups()
|  Needs to update extent tree root
|  ADD_DELAYED_REF to 315859712.
|  Delayed refs are attached to current trans handle.
|
|- __commit_transaction()
|- write_ctree_super()
|- btrfs_finish_extent_commit()
|- kfree(trans)
   Now delayed ref for 315859712 are lost

Transaction 712:
Tree block 315859712 get dropped
btrfs_commit_transaction()
|- btrfs_run_delayed_refs()
   |- run_one_delayed_ref()
      |- __free_extent()
         As previous ADD_DELAYED_REF to 315859712 is lost, extent tree
         doesn't have any backref for 315859712, causing the bug

In fact, commit c31edf610c ("btrfs-progs: Fix false ENOSPC alert by
tracking used space correctly") detects the tree block leakage, but in
the reproducer we have too much noise, thus nobody notices the leakage
warning.

[FIX]
We can't just move btrfs_run_delayed_refs() after
btrfs_write_dirty_block_groups(), as during btrfs_run_delayed_refs(), we
can re-dirty block groups.
Thus we need to exhaust both delayed refs and dirty blocks.

This patch will call btrfs_write_dirty_block_groups() and
btrfs_run_delayed_refs() in a loop until both delayed refs and dirty
blocks are exhausted. Much like what we do in commit_cowonly_roots() in
kernel.

Also, to prevent such problem from happening again (and not to debug
such problem again), add extra check on delayed refs before freeing the
transaction handle.

Reported-by: Klemens Schölhorn <klemens@schoelhorn.eu>
Issue: #187
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
2019-07-26 17:46:41 +02:00

246 lines
6.5 KiB
C

/*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public
* License v2 as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public
* License along with this program; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 021110-1307, USA.
*/
#include "kerncompat.h"
#include "disk-io.h"
#include "transaction.h"
#include "delayed-ref.h"
#include "common/messages.h"
struct btrfs_trans_handle* btrfs_start_transaction(struct btrfs_root *root,
int num_blocks)
{
struct btrfs_fs_info *fs_info = root->fs_info;
struct btrfs_trans_handle *h = kzalloc(sizeof(*h), GFP_NOFS);
if (fs_info->transaction_aborted)
return ERR_PTR(-EROFS);
if (!h)
return ERR_PTR(-ENOMEM);
if (root->commit_root) {
error("commit_root already set when starting transaction");
kfree(h);
return ERR_PTR(-EINVAL);
}
if (fs_info->running_transaction) {
error("attempt to start transaction over already running one");
kfree(h);
return ERR_PTR(-EINVAL);
}
h->fs_info = fs_info;
fs_info->running_transaction = h;
fs_info->generation++;
h->transid = fs_info->generation;
h->blocks_reserved = num_blocks;
h->reinit_extent_tree = false;
h->allocating_chunk = 0;
root->last_trans = h->transid;
root->commit_root = root->node;
extent_buffer_get(root->node);
return h;
}
static int update_cowonly_root(struct btrfs_trans_handle *trans,
struct btrfs_root *root)
{
int ret;
u64 old_root_bytenr;
struct btrfs_root *tree_root = root->fs_info->tree_root;
while(1) {
old_root_bytenr = btrfs_root_bytenr(&root->root_item);
if (old_root_bytenr == root->node->start)
break;
btrfs_set_root_bytenr(&root->root_item,
root->node->start);
btrfs_set_root_generation(&root->root_item,
trans->transid);
root->root_item.level = btrfs_header_level(root->node);
ret = btrfs_update_root(trans, tree_root,
&root->root_key,
&root->root_item);
if (ret < 0)
return ret;
btrfs_write_dirty_block_groups(trans);
}
return 0;
}
int commit_tree_roots(struct btrfs_trans_handle *trans,
struct btrfs_fs_info *fs_info)
{
struct btrfs_root *root;
struct list_head *next;
struct extent_buffer *eb;
int ret;
if (fs_info->readonly)
return 0;
eb = fs_info->tree_root->node;
extent_buffer_get(eb);
ret = btrfs_cow_block(trans, fs_info->tree_root, eb, NULL, 0, &eb);
free_extent_buffer(eb);
if (ret)
return ret;
/*
* If the above CoW is the first one to dirty the current tree_root,
* delayed refs for it won't be run until after this function has
* finished executing, meaning we won't process the extent tree root,
* which will have been added to ->dirty_cowonly_roots. So run
* delayed refs here as well.
*/
ret = btrfs_run_delayed_refs(trans, -1);
if (ret)
return ret;
while(!list_empty(&fs_info->dirty_cowonly_roots)) {
next = fs_info->dirty_cowonly_roots.next;
list_del_init(next);
root = list_entry(next, struct btrfs_root, dirty_list);
ret = update_cowonly_root(trans, root);
free_extent_buffer(root->commit_root);
root->commit_root = NULL;
if (ret < 0)
return ret;
}
return 0;
}
int __commit_transaction(struct btrfs_trans_handle *trans,
struct btrfs_root *root)
{
u64 start;
u64 end;
struct btrfs_fs_info *fs_info = root->fs_info;
struct extent_buffer *eb;
struct extent_io_tree *tree = &fs_info->extent_cache;
int ret;
while(1) {
ret = find_first_extent_bit(tree, 0, &start, &end,
EXTENT_DIRTY);
if (ret)
break;
while(start <= end) {
eb = find_first_extent_buffer(tree, start);
BUG_ON(!eb || eb->start != start);
ret = write_tree_block(trans, fs_info, eb);
BUG_ON(ret);
start += eb->len;
clear_extent_buffer_dirty(eb);
free_extent_buffer(eb);
}
}
return 0;
}
int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
struct btrfs_root *root)
{
u64 transid = trans->transid;
int ret = 0;
struct btrfs_fs_info *fs_info = root->fs_info;
struct btrfs_space_info *sinfo;
if (trans->fs_info->transaction_aborted)
return -EROFS;
/*
* Flush all accumulated delayed refs so that root-tree updates are
* consistent
*/
ret = btrfs_run_delayed_refs(trans, -1);
if (ret < 0)
goto error;
if (root->commit_root == root->node)
goto commit_tree;
if (root == root->fs_info->tree_root)
goto commit_tree;
if (root == root->fs_info->chunk_root)
goto commit_tree;
free_extent_buffer(root->commit_root);
root->commit_root = NULL;
btrfs_set_root_bytenr(&root->root_item, root->node->start);
btrfs_set_root_generation(&root->root_item, trans->transid);
root->root_item.level = btrfs_header_level(root->node);
ret = btrfs_update_root(trans, root->fs_info->tree_root,
&root->root_key, &root->root_item);
if (ret < 0)
goto error;
commit_tree:
ret = commit_tree_roots(trans, fs_info);
if (ret < 0)
goto error;
/*
* btrfs_write_dirty_block_groups() can cause COW thus new delayed
* tree refs, while run such delayed tree refs can dirty block groups
* again, we need to exhause both dirty blocks and delayed refs
*/
while (!RB_EMPTY_ROOT(&trans->delayed_refs.href_root) ||
test_range_bit(&fs_info->block_group_cache, 0, (u64)-1,
BLOCK_GROUP_DIRTY, 0)) {
ret = btrfs_write_dirty_block_groups(trans);
if (ret < 0)
goto error;
ret = btrfs_run_delayed_refs(trans, -1);
if (ret < 0)
goto error;
}
__commit_transaction(trans, root);
if (ret < 0)
goto error;
/* There should be no pending delayed refs now */
if (!RB_EMPTY_ROOT(&trans->delayed_refs.href_root)) {
error("uncommitted delayed refs detected");
goto error;
}
ret = write_ctree_super(trans);
btrfs_finish_extent_commit(trans);
kfree(trans);
free_extent_buffer(root->commit_root);
root->commit_root = NULL;
fs_info->running_transaction = NULL;
fs_info->last_trans_committed = transid;
list_for_each_entry(sinfo, &fs_info->space_info, list) {
if (sinfo->bytes_reserved) {
warning(
"reserved space leaked, transid=%llu flag=0x%llx bytes_reserved=%llu",
transid, sinfo->flags, sinfo->bytes_reserved);
}
}
return ret;
error:
btrfs_destroy_delayed_refs(trans);
free(trans);
return ret;
}
void btrfs_abort_transaction(struct btrfs_trans_handle *trans, int error)
{
trans->fs_info->transaction_aborted = error;
}