kernel/git/stable/linux.git/fs/btrfs/delayed-ref.c, branch linux-3.8.y

Btrfs: compare relevant parts of delayed tree refs

2013-05-11T20:54:09+00:00

commit 41b0fc42800569f63e029549b75c4c9cb63f2dfd upstream. A user reported a panic while running a balance. What was happening was he was relocating a block, which added the reference to the relocation tree. Then relocation would walk through the relocation tree and drop that reference and free that block, and then it would walk down a snapshot which referenced the same block and add another ref to the block. The problem is this was all happening in the same transaction, so the parent block was free'ed up when we drop our reference which was immediately available for allocation, and then it was used _again_ to add a reference for the same block from a different snapshot. This resulted in something like this in the delayed ref tree add ref to 90234880, parent=2067398656, ref_root 1766, level 1 del ref to 90234880, parent=2067398656, ref_root 18446744073709551608, level 1 add ref to 90234880, parent=2067398656, ref_root 1767, level 1 as you can see the ref_root's don't match, because when we inc the ref we use the header owner, which is the original tree the block belonged to, instead of the data reloc tree. Then when we remove the extent we use the reloc tree objectid. But none of this matters, since it is a shared reference which means only the parent matters. When the delayed ref stuff runs it adds all the increments first, and then does all the drops, to make sure that we don't delete the ref if we net a positive ref count. But tree blocks aren't allowed to have multiple refs from the same block, so this panics when it tries to add the second ref. We need the add and the drop to cancel each other out in memory so we only do the final add. So to fix this we need to adjust how the delayed refs are added to the tree. Only the ref_root matters when it is a normal backref, and only the parent matters when it is a shared backref. So make our decision based on what ref type we have. This allows us to keep the ref_root in memory in case anybody wants to use it for something else, and it allows the delayed refs to be merged properly so we don't end up with this panic. With this patch the users image no longer panics on mount, and it has a clean fsck after a normal mount/umount cycle. Thanks, Reported-by: Roman Mamedov Signed-off-by: Josef Bacik Signed-off-by: Greg Kroah-Hartman

Btrfs: allow delayed refs to be merged

2012-08-28T20:53:38+00:00

Daniel Blueman reported a bug with fio+balance on a ramdisk setup. Basically what happens is the balance relocates a tree block which will drop the implicit refs for all of its children and adds a full backref. Once the block is relocated we have to add the implicit refs back, so when we cow the block again we add the implicit refs for its children back. The problem comes when the original drop ref doesn't get run before we add the implicit refs back. The delayed ref stuff will specifically prefer ADD operations over DROP to keep us from freeing up an extent that will have references to it, so we try to add the implicit ref before it is actually removed and we panic. This worked fine before because the add would have just canceled the drop out and we would have been fine. But the backref walking work needs to be able to freeze the delayed ref stuff in time so we have this ever increasing sequence number that gets attached to all new delayed ref updates which makes us not merge refs and we run into this issue. So to fix this we need to merge delayed refs. So everytime we run a clustered ref we need to try and merge all of its delayed refs. The backref walking stuff locks the delayed ref head before processing, so if we have it locked we are safe to merge any refs inside of the sequence number. If there is no sequence number we can merge all refs. Doing this not only fixes our bug but keeps the delayed ref code from adding and removing useless refs and batching together multiple refs into one search instead of one search per delayed ref, which will really help our commit times. I ran this with Daniels test and 276 and I haven't seen any problems. Thanks, Reported-by: Daniel J Blueman Signed-off-by: Josef Bacik

Btrfs: fix deadlock in wait_for_more_refs

2012-08-28T20:53:32+00:00

Commit a168650c introduced a waiting mechanism to prevent busy waiting in btrfs_run_delayed_refs. This can deadlock with btrfs_run_ordered_operations, where a tree_mod_seq is held while waiting for the io to complete, while the end_io calls btrfs_run_delayed_refs. This whole mechanism is unnecessary. If not enough runnable refs are available to satisfy count, just return as count is more like a guideline than a strict requirement. In case we have to run all refs, commit transaction makes sure that no other threads are working in the transaction anymore, so we just assert here that no refs are blocked. Signed-off-by: Arne Jansen Signed-off-by: Chris Mason

Btrfs: hooks for qgroup to record delayed refs

2012-07-12T08:54:38+00:00

Hooks into qgroup code to record refs and into transaction commit. This is the main entry point for qgroup. Basically every change in extent backrefs got accounted to the appropriate qgroups. Signed-off-by: Arne Jansen Signed-off-by: Jan Schmidt

Btrfs: join tree mod log code with the code holding back delayed refs

2012-07-10T13:14:41+00:00

We've got two mechanisms both required for reliable backref resolving (tree mod log and holding back delayed refs). You cannot make use of one without the other. So instead of requiring the user of this mechanism to setup both correctly, we join them into a single interface. Additionally, we stop inserting non-blockers into fs_info->tree_mod_seq_list as we did before, which was of no value. Signed-off-by: Jan Schmidt

Btrfs: use delayed ref sequence numbers for all fs-tree updates

2012-05-30T16:18:21+00:00

The sequence number for delayed refs is needed to postpone certain delayed refs for a very short period while walking backrefs. Before the tree modification log, we thought we'd only have to hold back those references that don't have a counter operation. While now we've the tree mod log, we're rewinding fs tree blocks to a defined consistent state. We cannot know in advance for which tree block we'll be doing rewind operations later. Therefore, we must postpone all the delayed refs for fs-tree blocks, even those having a counter operation. Signed-off-by: Jan Schmidt

btrfs: return void in functions without error conditions

2012-03-22T00:45:34+00:00

Signed-off-by: Jeff Mahoney

btrfs: Fix kfree of member instead of structure

2012-03-22T00:45:30+00:00

Correctness fix: The kfree calls in the add_delayed_* functions free the node that's passed into it, but the node is a member of another structure. It works because it's always the first member of the containing structure, but it should really be using the containing structure itself. Signed-off-by: Jeff Mahoney

Btrfs: add waitqueue instead of doing busy waiting for more delayed refs

2012-01-04T15:12:48+00:00

Now that we may be holding back delayed refs for a limited period, we might end up having no runnable delayed refs. Without this commit, we'd do busy waiting in that thread until another (runnable) ref arives. Instead, we're detecting this situation and use a waitqueue, such that we only try to run more refs after a) another runnable ref was added or b) delayed refs are no longer held back Signed-off-by: Jan Schmidt

Btrfs: put back delayed refs that are too new

2012-01-04T15:12:45+00:00

When processing a delayed ref, first check if there are still old refs in the process of being added. If so, put this ref back to the tree. To avoid looping on this ref, choose a newer one in the next loop. btrfs_find_ref_cluster has to take care of that. Signed-off-by: Arne Jansen Signed-off-by: Jan Schmidt