leandrof/linux
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Btrfs: deal with convert_extent_bit errors to avoid fs corruption

Browse Source 
When committing a transaction or a log, we look for btree extents that
need to be durably persisted by searching for ranges in a io tree that
have some bits set (EXTENT_DIRTY or EXTENT_NEW). We then attempt to clear
those bits and set the EXTENT_NEED_WAIT bit, with calls to the function
convert_extent_bit, and then start writeback for the extents.

That function however can return an error (at the moment only -ENOMEM
is possible, specially when it does GFP_ATOMIC allocation requests
through alloc_extent_state_atomic) - that means the ranges didn't got
the EXTENT_NEED_WAIT bit set (or at least not for the whole range),
which in turn means a call to btrfs_wait_marked_extents() won't find
those ranges for which we started writeback, causing a transaction
commit or a log commit to persist a new superblock without waiting
for the writeback of extents in that range to finish first.

Therefore if a crash happens after persisting the new superblock and
before writeback finishes, we have a superblock pointing to roots that
weren't fully persisted or roots that point to nodes or leafs that weren't
fully persisted, causing all sorts of unexpected/bad behaviour as we endup
reading garbage from disk or the content of some node/leaf from a past
generation that got cowed or deleted and is no longer valid (for this later
case we end up getting error messages like "parent transid verify failed on
X wanted Y found Z" when reading btree nodes/leafs from disk).

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
This commit is contained in:
Filipe Manana 2014-10-13 12:28:37 +01:00 committed by Chris Mason
parent 2fc9f6baa2
commit 663dfbb077
2 changed files with 76 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

92
fs/btrfs/transaction.c
View File

@ -76,6 +76,32 @@ void btrfs_put_transaction(struct btrfs_transaction *transaction)
}
}
static void clear_btree_io_tree(struct extent_io_tree *tree)
{
spin_lock(&tree->lock);
while (!RB_EMPTY_ROOT(&tree->state)) {
struct rb_node *node;
struct extent_state *state;
node = rb_first(&tree->state);
state = rb_entry(node, struct extent_state, rb_node);
rb_erase(&state->rb_node, &tree->state);
RB_CLEAR_NODE(&state->rb_node);
/*
* btree io trees aren't supposed to have tasks waiting for
* changes in the flags of extent states ever.
*/
ASSERT(!waitqueue_active(&state->wq));
free_extent_state(state);
if (need_resched()) {
spin_unlock(&tree->lock);
cond_resched();
spin_lock(&tree->lock);
}
}
spin_unlock(&tree->lock);
}
static noinline void switch_commit_roots(struct btrfs_transaction *trans,
struct btrfs_fs_info *fs_info)
{
@ -89,6 +115,7 @@ static noinline void switch_commit_roots(struct btrfs_transaction *trans,
root->commit_root = btrfs_root_node(root);
if (is_fstree(root->objectid))
btrfs_unpin_free_ino(root);
clear_btree_io_tree(&root->dirty_log_pages);
}
up_write(&fs_info->commit_root_sem);
}
@ -828,17 +855,38 @@ int btrfs_write_marked_extents(struct btrfs_root *root,
while (!find_first_extent_bit(dirty_pages, start, &start, &end,
mark, &cached_state)) {
convert_extent_bit(dirty_pages, start, end, EXTENT_NEED_WAIT,
mark, &cached_state, GFP_NOFS);
cached_state = NULL;
err = filemap_fdatawrite_range(mapping, start, end);
bool wait_writeback = false;
err = convert_extent_bit(dirty_pages, start, end,
EXTENT_NEED_WAIT,
mark, &cached_state, GFP_NOFS);
/*
* convert_extent_bit can return -ENOMEM, which is most of the
* time a temporary error. So when it happens, ignore the error
* and wait for writeback of this range to finish - because we
* failed to set the bit EXTENT_NEED_WAIT for the range, a call
* to btrfs_wait_marked_extents() would not know that writeback
* for this range started and therefore wouldn't wait for it to
* finish - we don't want to commit a superblock that points to
* btree nodes/leafs for which writeback hasn't finished yet
* (and without errors).
* We cleanup any entries left in the io tree when committing
* the transaction (through clear_btree_io_tree()).
*/
if (err == -ENOMEM) {
err = 0;
wait_writeback = true;
}
if (!err)
err = filemap_fdatawrite_range(mapping, start, end);
if (err)
werr = err;
else if (wait_writeback)
werr = filemap_fdatawait_range(mapping, start, end);
cached_state = NULL;
cond_resched();
start = end + 1;
}
if (err)
werr = err;
return werr;
}
@ -862,9 +910,21 @@ int btrfs_wait_marked_extents(struct btrfs_root *root,
while (!find_first_extent_bit(dirty_pages, start, &start, &end,
EXTENT_NEED_WAIT, &cached_state)) {
clear_extent_bit(dirty_pages, start, end, EXTENT_NEED_WAIT,
0, 0, &cached_state, GFP_NOFS);
err = filemap_fdatawait_range(mapping, start, end);
/*
* Ignore -ENOMEM errors returned by clear_extent_bit().
* When committing the transaction, we'll remove any entries
* left in the io tree. For a log commit, we don't remove them
* after committing the log because the tree can be accessed
* concurrently - we do it only at transaction commit time when
* it's safe to do it (through clear_btree_io_tree()).
*/
err = clear_extent_bit(dirty_pages, start, end,
EXTENT_NEED_WAIT,
0, 0, &cached_state, GFP_NOFS);
if (err == -ENOMEM)
err = 0;
if (!err)
err = filemap_fdatawait_range(mapping, start, end);
if (err)
werr = err;
cond_resched();
@ -919,17 +979,17 @@ static int btrfs_write_and_wait_marked_extents(struct btrfs_root *root,
return 0;
}
int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,
static int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,
struct btrfs_root *root)
{
if (!trans || !trans->transaction) {
struct inode *btree_inode;
btree_inode = root->fs_info->btree_inode;
return filemap_write_and_wait(btree_inode->i_mapping);
}
return btrfs_write_and_wait_marked_extents(root,
int ret;
ret = btrfs_write_and_wait_marked_extents(root,
&trans->transaction->dirty_pages,
EXTENT_DIRTY);
clear_btree_io_tree(&trans->transaction->dirty_pages);
return ret;
}
/*

2
fs/btrfs/transaction.h
View File

@ -145,8 +145,6 @@ struct btrfs_trans_handle *btrfs_attach_transaction_barrier(
struct btrfs_root *root);
struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root);
int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid);
int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,
struct btrfs_root *root);
void btrfs_add_dead_root(struct btrfs_root *root);
int btrfs_defrag_root(struct btrfs_root *root);