On 1/22/21 10:28 AM, fdman...@kernel.org wrote:
From: Filipe Manana <fdman...@suse.com>
During log replay we first start by walking the log trees and pin the
ranges for their extent buffers, through calls to the function
btrfs_pin_extent_for_log_replay().
However if the space cache for a block group is invalid and needs to be
rebuilt, we can fail the log replay and mount with -EINVAL like this:
[72383.415114] BTRFS: device fsid 32b95b69-0ea9-496a-9f02-3f5a56dc9322 devid
1 transid 1432 /dev/sdb scanned by mount (3816007)
[72383.417837] BTRFS info (device sdb): disk space caching is enabled
[72383.418536] BTRFS info (device sdb): has skinny extents
[72383.423846] BTRFS info (device sdb): start tree-log replay
[72383.426416] BTRFS warning (device sdb): block group 30408704 has wrong
amount of free space
[72383.427686] BTRFS warning (device sdb): failed to load free space cache
for block group 30408704, rebuilding it now
[72383.454291] BTRFS: error (device sdb) in btrfs_recover_log_trees:6203:
errno=-22 unknown (Failed to pin buffers while recovering log root tree.)
[72383.456725] BTRFS: error (device sdb) in btrfs_replay_log:2253: errno=-22
unknown (Failed to recover log tree)
[72383.460241] BTRFS error (device sdb): open_ctree failed
This is because at the start of btrfs_pin_extent_for_log_replay() we mark
the range for the extent buffer in excluded extents io tree. That is fine
when the space cache is valid on disk and we can load it, in which case it
causes no problems - in fact it is pointless since shortly after, still at
btrfs_pin_extent_for_log_replay(), we remove the range from the free space
cache with the call to btrfs_remove_free_space(().
However, for the case where we need to rebuild the space cache, because it
is either invalid or it is missing, having the extent buffer range marked
in the excluded extents io tree leads to a -EINVAL failure from the call
to btrfs_remove_free_space(), resulting in the log replay and mount to
fail. This is because by having the range marked in the excluded extents
io tree, the caching thread ends never marking adding the range of the
extent buffer marked as free space in the block group since the calls to
add_new_free_space(), called from load_extent_tree_free(), filter out any
ranges that are marked as excluded extents.
So fix this by not marking the extent buffer range in the excluded extents
io tree at btrfs_pin_extent_for_log_replay() since it leads to the failure
when a space cache needs to be rebuilt and it is useless when we do not
need to rebuild a space cache. Also, remove the cleanup of ranges in the
excluded extents io tree at btrfs_finish_extent_commit() since they were
there to cleanup the ranges added by btrfs_pin_extent_for_log_replay().
Fixes: f2fb72983bdcf5 ("btrfs: Mark pinned log extents as excluded")
Signed-off-by: Filipe Manana <fdman...@suse.com>
Hmm it took some time to convince myself this is correct, but because we
unconditionally do that remove we really have to force ourselves to cache the
block group every time. That means my suggestion to do
if (btrfs_test_opt(fs_info, SPACE_CACHE))
cache block group
would actually cause problems with this patch as well. I think the best course
of action is to get rid of this idea that we can do it the fast way or skip it
altogether now, and just force a full caching of any block group at log replay
time and then this patch will be the right thing to do. You can add
Reviewed-by: Josef Bacik <jo...@toxicpanda.com>
Thanks,
Josef
