wireguard-linux/fs/btrfs/backref.c, branch jd/unified-crypt-queue

btrfs: do not resolve backrefs for roots that are being deleted

2020-03-23T16:03:51Z

Zygo reported a deadlock where a task was stuck in the inode logical resolve code. The deadlock looks like this Task 1 btrfs_ioctl_logical_to_ino ->iterate_inodes_from_logical ->iterate_extent_inodes ->path->search_commit_root isn't set, so a transaction is started ->resolve_indirect_ref for a root that's being deleted ->search for our key, attempt to lock a node, DEADLOCK Task 2 btrfs_drop_snapshot ->walk down to a leaf, lock it, walk up, lock node ->end transaction ->start transaction -> wait_cur_trans Task 3 btrfs_commit_transaction ->wait_event(cur_trans->write_wait, num_writers == 1) DEADLOCK We are holding a transaction open in btrfs_ioctl_logical_to_ino while we try to resolve our references. btrfs_drop_snapshot() holds onto its locks while it stops and starts transaction handles, because it assumes nobody is going to touch the root now. Commit just does what commit does, waiting for the writers to finish, blocking any new trans handles from starting. Fix this by making the backref code not try to resolve backrefs of roots that are currently being deleted. This will keep us from walking into a snapshot that's currently being deleted. This problem was harder to hit before because we rarely broke out of the snapshot delete halfway through, but with my delayed ref throttling code it happened much more often. However we've always been able to do this, so it's not a new problem. Fixes: 8da6d5815c59 ("Btrfs: added btrfs_find_all_roots()") Signed-off-by: Josef Bacik Signed-off-by: David Sterba

btrfs: kill the subvol_srcu

2020-03-23T16:02:00Z

Now that we have proper root ref counting everywhere we can kill the subvol_srcu. * removal of fs_info::subvol_srcu reduces size of fs_info by 1176 bytes * the refcount_t used for the references checks for accidental 0->1 in cases where the root lifetime would not be properly protected * there's a leak detector for roots to catch unfreed roots at umount time * SRCU served us well over the years but is was not a proper synchronization mechanism for some cases Signed-off-by: Josef Bacik Reviewed-by: David Sterba [ update changelog ] Signed-off-by: David Sterba

btrfs: relocation: Use btrfs_find_all_leafs to locate data extent parent tree leaves

2020-03-23T16:01:57Z

In relocation, we need to locate all parent tree leaves referring to one data extent, thus we have a complex mechanism to iterate throught extent tree and subvolume trees to locate the related leaves. However this is already done in backref.c, we have btrfs_find_all_leafs(), which can return a ulist containing all leaves referring to that data extent. Use btrfs_find_all_leafs() to replace find_data_references(). There is a special handling for v1 space cache data extents, where we need to delete the v1 space cache data extents, to avoid those data extents to hang the data relocation. In this patch, the special handling is done by re-iterating the root tree leaf. Although it's a little less efficient than the old handling, considering we can reuse a lot of code, it should be acceptable. Signed-off-by: Qu Wenruo Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: backref, use correct count to resolve normal data refs

2020-03-23T16:01:40Z

With the following patches: - btrfs: backref, only collect file extent items matching backref offset - btrfs: backref, not adding refs from shared block when resolving normal backref - btrfs: backref, only search backref entries from leaves of the same root we only collect the normal data refs we want, so the imprecise upper bound total_refs of that EXTENT_ITEM could now be changed to the count of the normal backref entry we want to search. Background and how the patches fit together: Btrfs has two types of data backref. For BTRFS_EXTENT_DATA_REF_KEY type of backref, we don't have the exact block number. Therefore, we need to call resolve_indirect_refs. It uses btrfs_search_slot to locate the leaf block. Then we need to walk through the leaves to search for the EXTENT_DATA items that have disk bytenr matching the extent item (add_all_parents). When resolving indirect refs, we could take entries that don't belong to the backref entry we are searching for right now. For that reason when searching backref entry, we always use total refs of that EXTENT_ITEM rather than individual count. For example: item 11 key (40831553536 EXTENT_ITEM 4194304) itemoff 15460 itemsize extent refs 24 gen 7302 flags DATA shared data backref parent 394985472 count 10 #1 extent data backref root 257 objectid 260 offset 1048576 count 3 #2 extent data backref root 256 objectid 260 offset 65536 count 6 #3 extent data backref root 257 objectid 260 offset 65536 count 5 #4 For example, when searching backref entry #4, we'll use total_refs 24, a very loose loop ending condition, instead of total_refs = 5. But using total_refs = 24 is not accurate. Sometimes, we'll never find all the refs from specific root. As a result, the loop keeps on going until we reach the end of that inode. The first 3 patches, handle 3 different types refs we might encounter. These refs do not belong to the normal backref we are searching, and hence need to be skipped. This patch changes the total_refs to correct number so that we could end loop as soon as we find all the refs we want. btrfs send uses backref to find possible clone sources, the following is a simple test to compare the results with and without this patch: $ btrfs subvolume create /sub1 $ for i in `seq 1 163840`; do dd if=/dev/zero of=/sub1/file bs=64K count=1 seek=$((i-1)) conv=notrunc oflag=direct done $ btrfs subvolume snapshot /sub1 /sub2 $ for i in `seq 1 163840`; do dd if=/dev/zero of=/sub1/file bs=4K count=1 seek=$(((i-1)*16+10)) conv=notrunc oflag=direct done $ btrfs subvolume snapshot -r /sub1 /snap1 $ time btrfs send /snap1 | btrfs receive /volume2 Without this patch: real 69m48.124s user 0m50.199s sys 70m15.600s With this patch: real 1m59.683s user 0m35.421s sys 2m42.684s Reviewed-by: Josef Bacik Reviewed-by: Johannes Thumshirn Signed-off-by: ethanwu [ add patchset cover letter with background and numbers ] Signed-off-by: David Sterba

btrfs: backref, only search backref entries from leaves of the same root

2020-03-23T16:01:40Z

We could have some nodes/leaves in subvolume whose owner are not the that subvolume. In this way, when we resolve normal backrefs of that subvolume, we should avoid collecting those references from these blocks. Reviewed-by: Josef Bacik Reviewed-by: Johannes Thumshirn Signed-off-by: ethanwu Signed-off-by: David Sterba

btrfs: backref, don't add refs from shared block when resolving normal backref

2020-03-23T16:01:40Z

All references from the block of SHARED_DATA_REF belong to that shared block backref. For example: item 11 key (40831553536 EXTENT_ITEM 4194304) itemoff 15460 itemsize 95 extent refs 24 gen 7302 flags DATA extent data backref root 257 objectid 260 offset 65536 count 5 extent data backref root 258 objectid 265 offset 0 count 9 shared data backref parent 394985472 count 10 Block 394985472 might be leaf from root 257, and the item obejctid and (file_pos - file_extent_item::offset) in that leaf just happens to be 260 and 65536 which is equal to the first extent data backref entry. Before this patch, when we resolve backref: root 257 objectid 260 offset 65536 we will add those refs in block 394985472 and wrongly treat those as the refs we want. Fix this by checking if the leaf we are processing is shared data backref, if so, just skip this leaf. Shared data refs added into preftrees.direct have all entry value = 0 (root_id = 0, key = NULL, level = 0) except parent entry. Other refs from indirect tree will have key value and root id != 0, and these values won't be changed when their parent is resolved and added to preftrees.direct. Therefore, we could reuse the preftrees.direct and search ref with all values = 0 except parent is set to avoid getting those resolved refs block. Reviewed-by: Josef Bacik Reviewed-by: Johannes Thumshirn Signed-off-by: ethanwu Signed-off-by: David Sterba

btrfs: backref, only collect file extent items matching backref offset

2020-03-23T16:01:40Z

When resolving one backref of type EXTENT_DATA_REF, we collect all references that simply reference the EXTENT_ITEM even though their (file_pos - file_extent_item::offset) are not the same as the btrfs_extent_data_ref::offset we are searching for. This patch adds additional check so that we only collect references whose (file_pos - file_extent_item::offset) == btrfs_extent_data_ref::offset. Reviewed-by: Josef Bacik Reviewed-by: Johannes Thumshirn Signed-off-by: ethanwu Signed-off-by: David Sterba

btrfs: rename btrfs_put_fs_root and btrfs_grab_fs_root

2020-03-23T16:01:33Z

We are now using these for all roots, rename them to btrfs_put_root() and btrfs_grab_root(); Reviewed-by: Nikolay Borisov Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: push btrfs_grab_fs_root into btrfs_get_fs_root

2020-03-23T16:01:32Z

Now that all callers of btrfs_get_fs_root are subsequently calling btrfs_grab_fs_root and handling dropping the ref when they are done appropriately, go ahead and push btrfs_grab_fs_root up into btrfs_get_fs_root. Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: hold a ref on the root in resolve_indirect_ref

2020-03-23T16:01:27Z

We're looking up a random root, we need to hold a ref on it while we're using it. Reviewed-by: David Sterba Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba