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btrfs: warn about extent buffer that can not be released

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When we unmount the fs or during mount failures, btrfs will call
invalidate_inode_pages() to release all btree inode folios.

However that function can return -EBUSY if any folios can not be
invalidated.
This can be caused by:

- Some extent buffers are still held by btrfs
  This is a logic error, as we should release all tree root nodes
  during unmount and mount failure handling.

- Some extent buffers are under readahead and haven't yet finished
  These are much rarer but valid cases.
  In that case we should wait for those extent buffers.

Introduce a new helper invalidate_and_check_btree_folios() which will:

- Call invalidate_inode_pages2() and catch its return value
  If it returned 0 as expected, that's great and we can call it a day.

- Otherwise go through each extent buffer in buffer_tree
  Increase the ref by one first for the eb we're checking.
  This is to ensure the eb won't be freed after the readahead is
  finished.

  For ebs that still have EXTENT_BUFFER_READING flag, wait for them to
  finish first.

  After waiting for the readahead, check the refs of the eb and if it's
  still dirty.

  If the eb ref count is greater than 2 (one for the buffer tree, one
  held by us), it means we are still holding the extent buffer somewhere
  else, which is a code bug.

  If the eb is still dirty, it means a bug in transaction handling, e.g.
  the bug fixed by patch "btrfs: only release the dirty pages io tree
  after successful writes".

  For either case, show a warning message about the eb, including its
  bytenr, owner, refs and flags.
  And if it's a debug build, also trigger WARN_ON_ONCE() so that fstests
  can properly catch such situation.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=221270
Reported-by: AHN SEOK-YOUNG <iamsyahn@gmail.com>
CC: Teng Liu <27rabbitlt@gmail.com>
Tested-by: Teng Liu <27rabbitlt@gmail.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo 2026-04-30 10:37:23 +09:30 • committed by David Sterba
commit 83f7e52b7e
3 changed files with 57 additions and 8 deletions
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