kernel.git/fs/btrfs/delayed-ref.c, branch linux-6.10.y

btrfs: check delayed refs when we're checking if a ref exists

2024-08-29T15:35:42Z

commit 42fac187b5c746227c92d024f1caf33bc1d337e4 upstream. In the patch 78c52d9eb6b7 ("btrfs: check for refs on snapshot delete resume") I added some code to handle file systems that had been corrupted by a bug that incorrectly skipped updating the drop progress key while dropping a snapshot. This code would check to see if we had already deleted our reference for a child block, and skip the deletion if we had already. Unfortunately there is a bug, as the check would only check the on-disk references. I made an incorrect assumption that blocks in an already deleted snapshot that was having the deletion resume on mount wouldn't be modified. If we have 2 pending deleted snapshots that share blocks, we can easily modify the rules for a block. Take the following example subvolume a exists, and subvolume b is a snapshot of subvolume a. They share references to block 1. Block 1 will have 2 full references, one for subvolume a and one for subvolume b, and it belongs to subvolume a (btrfs_header_owner(block 1) == subvolume a). When deleting subvolume a, we will drop our full reference for block 1, and because we are the owner we will drop our full reference for all of block 1's children, convert block 1 to FULL BACKREF, and add a shared reference to all of block 1's children. Then we will start the snapshot deletion of subvolume b. We look up the extent info for block 1, which checks delayed refs and tells us that FULL BACKREF is set, so sets parent to the bytenr of block 1. However because this is a resumed snapshot deletion, we call into check_ref_exists(). Because check_ref_exists() only looks at the disk, it doesn't find the shared backref for the child of block 1, and thus returns 0 and we skip deleting the reference for the child of block 1 and continue. This orphans the child of block 1. The fix is to lookup the delayed refs, similar to what we do in btrfs_lookup_extent_info(). However we only care about whether the reference exists or not. If we fail to find our reference on disk, go look up the bytenr in the delayed refs, and if it exists look for an existing ref in the delayed ref head. If that exists then we know we can delete the reference safely and carry on. If it doesn't exist we know we have to skip over this block. This bug has existed since I introduced this fix, however requires having multiple deleted snapshots pending when we unmount. We noticed this in production because our shutdown path stops the container on the system, which deletes a bunch of subvolumes, and then reboots the box. This gives us plenty of opportunities to hit this issue. Looking at the history we've seen this occasionally in production, but we had a big spike recently thanks to faster machines getting jobs with multiple subvolumes in the job. Chris Mason wrote a reproducer which does the following mount /dev/nvme4n1 /btrfs btrfs subvol create /btrfs/s1 simoop -E -f 4k -n 200000 -z /btrfs/s1 while(true) ; do btrfs subvol snap /btrfs/s1 /btrfs/s2 simoop -f 4k -n 200000 -r 10 -z /btrfs/s2 btrfs subvol snap /btrfs/s2 /btrfs/s3 btrfs balance start -dusage=80 /btrfs btrfs subvol del /btrfs/s2 /btrfs/s3 umount /btrfs btrfsck /dev/nvme4n1 || exit 1 mount /dev/nvme4n1 /btrfs done On the second loop this would fail consistently, with my patch it has been running for hours and hasn't failed. I also used dm-log-writes to capture the state of the failure so I could debug the problem. Using the existing failure case to test my patch validated that it fixes the problem. Fixes: 78c52d9eb6b7 ("btrfs: check for refs on snapshot delete resume") CC: stable@vger.kernel.org # 5.4+ Reviewed-by: Filipe Manana Signed-off-by: Josef Bacik Signed-off-by: David Sterba Signed-off-by: Greg Kroah-Hartman

btrfs: replace btrfs_delayed__ref with btrfs__ref

2024-05-07T19:31:05Z

Now that these two structs are the same, move the btrfs_data_ref and btrfs_tree_ref up and use these in the btrfs_delayed_ref_node. Then remove the btrfs_delayed_*_ref structs. Reviewed-by: Filipe Manana Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: rename btrfs_data_ref->ino to ->objectid

2024-05-07T19:31:05Z

This is how we refer to it in the rest of the extent reference related code, make it consistent. Reviewed-by: Filipe Manana Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: move ->parent and ->ref_root into btrfs_delayed_ref_node

2024-05-07T19:31:05Z

These two members are shared by both the tree refs and data refs, so move them into btrfs_delayed_ref_node proper. This allows us to greatly simplify the comparison code, as the shared refs always only sort on parent, and the non shared refs always sort first on ref_root, and then only data refs sort on their specific fields. Reviewed-by: Filipe Manana Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: rename ->len to ->num_bytes in btrfs_ref

2024-05-07T19:31:05Z

We consistently use ->num_bytes everywhere through the delayed ref code, except in btrfs_ref. Rename btrfs_ref to match all the other code. Reviewed-by: Filipe Manana Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: unify the btrfs_add_delayed_*_ref helpers into one helper

2024-05-07T19:31:05Z

Now that these helpers are identical, create a helper function that handles everything properly and strip the individual helpers down to use just the common helper. This cleans up a significant amount of duplicated code. Reviewed-by: Filipe Manana Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: simplify delayed ref tracepoints

2024-05-07T19:31:04Z

Now that all of the delayed ref information is in the delayed ref node, drastically simplify the delayed ref tracepoints by simply passing in the btrfs_delayed_ref_node and populating the tracepoints with the values from the structure itself. Reviewed-by: Filipe Manana Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: move ref specific initialization into init_delayed_ref_common

2024-05-07T19:31:04Z

Now that the btrfs_delayed_ref_node contains a union of the data and metadata specific information we can move the initialization into init_delayed_ref_common and just use the btrfs_ref to initialize the correct fields of the reference. Reviewed-by: Filipe Manana Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: initialize btrfs_delayed_ref_head with btrfs_ref

2024-05-07T19:31:04Z

We are calling init_delayed_ref_head with all of the elements from btrfs_ref, clean this up to simply pass in the btrfs_ref and initialize the btrfs_delayed_ref_head with the values from the btrfs_ref directly. Reviewed-by: Filipe Manana Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: pass btrfs_ref to init_delayed_ref_common

2024-05-07T19:31:04Z

We're extracting all of these values from the btrfs_ref we passed in already, just pass the btrfs_ref through to init_delayed_ref_common and get the values directly from the struct. Reviewed-by: Filipe Manana Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba

kernel.git/fs/btrfs/delayed-ref.c, branch linux-6.10.y

btrfs: check delayed refs when we're checking if a ref exists

btrfs: replace btrfs_delayed_*_ref with btrfs_*_ref

btrfs: rename btrfs_data_ref->ino to ->objectid

btrfs: move ->parent and ->ref_root into btrfs_delayed_ref_node

btrfs: rename ->len to ->num_bytes in btrfs_ref

btrfs: unify the btrfs_add_delayed_*_ref helpers into one helper

btrfs: simplify delayed ref tracepoints

btrfs: move ref specific initialization into init_delayed_ref_common

btrfs: initialize btrfs_delayed_ref_head with btrfs_ref

btrfs: pass btrfs_ref to init_delayed_ref_common

btrfs: replace btrfs_delayed__ref with btrfs__ref