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btrfs: explicitly protect ->last_byte_to_unpin in unpin_extent_range

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Currently unpin_extent_range happens in the transaction commit context,
so we are protected from ->last_byte_to_unpin changing while we're
unpinning, because any new transactions would have to wait for us to
complete before modifying ->last_byte_to_unpin.

However in the future we may want to change how this works, for instance
with async unpinning or other such TODO items.  To prepare for that
future explicitly protect ->last_byte_to_unpin with the commit_root_sem
so we are sure it won't change while we're doing our work.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Josef Bacik 2020-10-23 09:58:06 -04:00 committed by David Sterba
parent 27d56e62e4
commit 2ca08c56e8
1 changed files with 2 additions and 0 deletions
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2
fs/btrfs/extent-tree.c
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@ -2769,11 +2769,13 @@ static int unpin_extent_range(struct btrfs_fs_info *fs_info,
len = cache->start + cache->length - start;
len = min(len, end + 1 - start);
down_read(&fs_info->commit_root_sem);
if (start < cache->last_byte_to_unpin && return_free_space) {
u64 add_len = min(len, cache->last_byte_to_unpin - start);
btrfs_add_free_space(cache, start, add_len);
}
up_read(&fs_info->commit_root_sem);
start += len;
total_unpinned += len;