On Mon, 4 Mar 2013 18:54:02 +0800, Liu Bo wrote:
> On Mon, Mar 04, 2013 at 05:44:29PM +0800, Miao Xie wrote:
>> There are several bugs at error path of create_snapshot() when the
>> transaction commitment failed.
>> - access the freed transaction handler. At the end of the
>> transaction commitment, the transaction handler was freed, so we
>> should not access it after the transaction commitment.
>> - we were not aware of the error which happened during the snapshot
>> creation if we submitted a async transaction commitment.
>> - pending snapshot access vs pending snapshot free. when something
>> wrong happened after we submitted a async transaction commitment,
>> the transaction committer would cleanup the pending snapshots and
>> free them. But the snapshot creators were not aware of it, they
>> would access the freed pending snapshots.
>>
>> This patch fixes the above problems by:
>> - remove the dangerous code that accessed the freed handler
>> - assign ->error if the error happens during the snapshot creation
>> - the transaction committer doesn't free the pending snapshots,
>> just assigns the error number and evicts them before we unblock
>> the transaction.
>>
>> Reported-by: Dan Carpenter <[email protected]>
>> Signed-off-by: Miao Xie <[email protected]>
>> ---
>> fs/btrfs/disk-io.c | 16 +++++-------
>> fs/btrfs/ioctl.c | 6 +----
>> fs/btrfs/transaction.c | 58
>> +++++++++++++++++++++++++++--------------------
>> 3 files changed, 41 insertions(+), 39 deletions(-)
>>
>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>> index 02369a3..7d84651 100644
>> --- a/fs/btrfs/disk-io.c
>> +++ b/fs/btrfs/disk-io.c
>> @@ -62,7 +62,7 @@ static void btrfs_destroy_ordered_operations(struct
>> btrfs_transaction *t,
>> static void btrfs_destroy_ordered_extents(struct btrfs_root *root);
>> static int btrfs_destroy_delayed_refs(struct btrfs_transaction *trans,
>> struct btrfs_root *root);
>> -static void btrfs_destroy_pending_snapshots(struct btrfs_transaction *t);
>> +static void btrfs_evict_pending_snapshots(struct btrfs_transaction *t);
>> static void btrfs_destroy_delalloc_inodes(struct btrfs_root *root);
>> static int btrfs_destroy_marked_extents(struct btrfs_root *root,
>> struct extent_io_tree *dirty_pages,
>> @@ -3687,7 +3687,7 @@ int btrfs_destroy_delayed_refs(struct
>> btrfs_transaction *trans,
>> return ret;
>> }
>>
>> -static void btrfs_destroy_pending_snapshots(struct btrfs_transaction *t)
>> +static void btrfs_evict_pending_snapshots(struct btrfs_transaction *t)
>> {
>> struct btrfs_pending_snapshot *snapshot;
>> struct list_head splice;
>> @@ -3700,10 +3700,8 @@ static void btrfs_destroy_pending_snapshots(struct
>> btrfs_transaction *t)
>> snapshot = list_entry(splice.next,
>> struct btrfs_pending_snapshot,
>> list);
>> -
>> + snapshot->error = -ECANCELED;
>
> ECANCELED or EROFS? Now that EROFS is why we're here.
If trans->blocks_used is not 0, the file system may not be set to read-only, so
I chose ECANCELED,
this error number is proper, I think.
Thanks
Miao
> Others look good.
>
> thanks,
> liubo
>
>> list_del_init(&snapshot->list);
>> -
>> - kfree(snapshot);
>> }
>> }
>>
>> @@ -3840,6 +3838,8 @@ void btrfs_cleanup_one_transaction(struct
>> btrfs_transaction *cur_trans,
>> cur_trans->blocked = 1;
>> wake_up(&root->fs_info->transaction_blocked_wait);
>>
>> + btrfs_evict_pending_snapshots(cur_trans);
>> +
>> cur_trans->blocked = 0;
>> wake_up(&root->fs_info->transaction_wait);
>>
>> @@ -3849,8 +3849,6 @@ void btrfs_cleanup_one_transaction(struct
>> btrfs_transaction *cur_trans,
>> btrfs_destroy_delayed_inodes(root);
>> btrfs_assert_delayed_root_empty(root);
>>
>> - btrfs_destroy_pending_snapshots(cur_trans);
>> -
>> btrfs_destroy_marked_extents(root, &cur_trans->dirty_pages,
>> EXTENT_DIRTY);
>> btrfs_destroy_pinned_extent(root,
>> @@ -3894,6 +3892,8 @@ int btrfs_cleanup_transaction(struct btrfs_root *root)
>> if (waitqueue_active(&root->fs_info->transaction_blocked_wait))
>> wake_up(&root->fs_info->transaction_blocked_wait);
>>
>> + btrfs_evict_pending_snapshots(t);
>> +
>> t->blocked = 0;
>> smp_mb();
>> if (waitqueue_active(&root->fs_info->transaction_wait))
>> @@ -3907,8 +3907,6 @@ int btrfs_cleanup_transaction(struct btrfs_root *root)
>> btrfs_destroy_delayed_inodes(root);
>> btrfs_assert_delayed_root_empty(root);
>>
>> - btrfs_destroy_pending_snapshots(t);
>> -
>> btrfs_destroy_delalloc_inodes(root);
>>
>> spin_lock(&root->fs_info->trans_lock);
>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>> index b908960..94c0e42 100644
>> --- a/fs/btrfs/ioctl.c
>> +++ b/fs/btrfs/ioctl.c
>> @@ -596,12 +596,8 @@ static int create_snapshot(struct btrfs_root *root,
>> struct inode *dir,
>> ret = btrfs_commit_transaction(trans,
>> root->fs_info->extent_root);
>> }
>> - if (ret) {
>> - /* cleanup_transaction has freed this for us */
>> - if (trans->aborted)
>> - pending_snapshot = NULL;
>> + if (ret)
>> goto fail;
>> - }
>>
>> ret = pending_snapshot->error;
>> if (ret)
>> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
>> index f11c2e0..d8fce6f 100644
>> --- a/fs/btrfs/transaction.c
>> +++ b/fs/btrfs/transaction.c
>> @@ -1053,7 +1053,12 @@ int btrfs_defrag_root(struct btrfs_root *root)
>>
>> /*
>> * new snapshots need to be created at a very specific time in the
>> - * transaction commit. This does the actual creation
>> + * transaction commit. This does the actual creation.
>> + *
>> + * Note:
>> + * If the error which may affect the commitment of the current transaction
>> + * happens, we should return the error number. If the error which just
>> affect
>> + * the creation of the pending snapshots, just return 0.
>> */
>> static noinline int create_pending_snapshot(struct btrfs_trans_handle
>> *trans,
>> struct btrfs_fs_info *fs_info,
>> @@ -1072,7 +1077,7 @@ static noinline int create_pending_snapshot(struct
>> btrfs_trans_handle *trans,
>> struct extent_buffer *tmp;
>> struct extent_buffer *old;
>> struct timespec cur_time = CURRENT_TIME;
>> - int ret;
>> + int ret = 0;
>> u64 to_reserve = 0;
>> u64 index = 0;
>> u64 objectid;
>> @@ -1081,40 +1086,36 @@ static noinline int create_pending_snapshot(struct
>> btrfs_trans_handle *trans,
>>
>> path = btrfs_alloc_path();
>> if (!path) {
>> - ret = pending->error = -ENOMEM;
>> - return ret;
>> + pending->error = -ENOMEM;
>> + return 0;
>> }
>>
>> new_root_item = kmalloc(sizeof(*new_root_item), GFP_NOFS);
>> if (!new_root_item) {
>> - ret = pending->error = -ENOMEM;
>> + pending->error = -ENOMEM;
>> goto root_item_alloc_fail;
>> }
>>
>> - ret = btrfs_find_free_objectid(tree_root, &objectid);
>> - if (ret) {
>> - pending->error = ret;
>> + pending->error = btrfs_find_free_objectid(tree_root, &objectid);
>> + if (pending->error)
>> goto no_free_objectid;
>> - }
>>
>> btrfs_reloc_pre_snapshot(trans, pending, &to_reserve);
>>
>> if (to_reserve > 0) {
>> - ret = btrfs_block_rsv_add(root, &pending->block_rsv,
>> - to_reserve,
>> - BTRFS_RESERVE_NO_FLUSH);
>> - if (ret) {
>> - pending->error = ret;
>> + pending->error = btrfs_block_rsv_add(root,
>> + &pending->block_rsv,
>> + to_reserve,
>> + BTRFS_RESERVE_NO_FLUSH);
>> + if (pending->error)
>> goto no_free_objectid;
>> - }
>> }
>>
>> - ret = btrfs_qgroup_inherit(trans, fs_info, root->root_key.objectid,
>> - objectid, pending->inherit);
>> - if (ret) {
>> - pending->error = ret;
>> + pending->error = btrfs_qgroup_inherit(trans, fs_info,
>> + root->root_key.objectid,
>> + objectid, pending->inherit);
>> + if (pending->error)
>> goto no_free_objectid;
>> - }
>>
>> key.objectid = objectid;
>> key.offset = (u64)-1;
>> @@ -1142,7 +1143,7 @@ static noinline int create_pending_snapshot(struct
>> btrfs_trans_handle *trans,
>> dentry->d_name.len, 0);
>> if (dir_item != NULL && !IS_ERR(dir_item)) {
>> pending->error = -EEXIST;
>> - goto fail;
>> + goto dir_item_existed;
>> } else if (IS_ERR(dir_item)) {
>> ret = PTR_ERR(dir_item);
>> btrfs_abort_transaction(trans, root, ret);
>> @@ -1273,6 +1274,8 @@ static noinline int create_pending_snapshot(struct
>> btrfs_trans_handle *trans,
>> if (ret)
>> btrfs_abort_transaction(trans, root, ret);
>> fail:
>> + pending->error = ret;
>> +dir_item_existed:
>> trans->block_rsv = rsv;
>> trans->bytes_reserved = 0;
>> no_free_objectid:
>> @@ -1288,12 +1291,17 @@ root_item_alloc_fail:
>> static noinline int create_pending_snapshots(struct btrfs_trans_handle
>> *trans,
>> struct btrfs_fs_info *fs_info)
>> {
>> - struct btrfs_pending_snapshot *pending;
>> + struct btrfs_pending_snapshot *pending, *next;
>> struct list_head *head = &trans->transaction->pending_snapshots;
>> + int ret = 0;
>>
>> - list_for_each_entry(pending, head, list)
>> - create_pending_snapshot(trans, fs_info, pending);
>> - return 0;
>> + list_for_each_entry_safe(pending, next, head, list) {
>> + list_del(&pending->list);
>> + ret = create_pending_snapshot(trans, fs_info, pending);
>> + if (ret)
>> + break;
>> + }
>> + return ret;
>> }
>>
>> static void update_super_roots(struct btrfs_root *root)
>> --
>> 1.6.5.2
>> --
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