[PATCH 0/3] btrfs: fix possible race between error handling and writeback

[Qu Wenruo <wqu@suse.com>]

There are some rare kernel warning for experimental btrfs builds that
the DEBUG_WARN() can be triggered from btrfs_writepage_cow_fixup(),
mostly after some delalloc range failure.

The root cause is explained the the last patch, the TL;DR is we
shouldn't call btrfs_cleanup_ordered_extents() on folios that are
already unlocked.

Those unlocked folios can be under writeback, and if we cleared the
order flag just before the writeback thread entering
btrfs_writepage_cow_fixup(), we will trigger the warning.

The first patch is a small enhancement to the error messages, which
helps debugging.

The second patch is to make nocow_one_range() to do proper cleanup,
aligning itself to cow_file_range().

The last one is to fix the race window by keep folios of successful
ranges locked, so that we either unlock them manually at the end of
run_delalloc_nocow(), or get btrfs_cleanup_ordered_extents() called on
locked folios for error handling.

Qu Wenruo (3):
  btrfs: enhance error messages for delalloc range failure
  btrfs: make nocow_one_range() to do cleanup on error
  btrfs: keep folios locked inside run_delalloc_nocow()

 fs/btrfs/inode.c | 131 +++++++++++++++++++++--------------------------
 1 file changed, 58 insertions(+), 73 deletions(-)

-- 
2.50.0