Btrfs: fix race of using total_bytes_pinned
This percpu counter @total_bytes_pinned is introduced to skip unnecessary operations of 'commit transaction', it accounts for those space we may free but are stuck in delayed refs. And we zero out @space_info->total_bytes_pinned every transaction period so we have a better idea of how much space we'll actually free up by committing this transaction. However, we do the 'zero out' part a little earlier, before we actually unpin space, so we end up returning ENOSPC when we actually have free space that's just unpinned from committing transaction. xfstests/generic/074 complained then. This fixes it by actually accounting the percpu pinned number when 'unpin', and since it's protected by space_info->lock, the race is gone now. Signed-off-by: Liu Bo <bo.li.liu@oracle.com> Reviewed-by: Miao Xie <miaox@cn.fujitsu.com> Signed-off-by: Chris Mason <clm@fb.com>
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@ -5678,7 +5678,6 @@ void btrfs_prepare_extent_commit(struct btrfs_trans_handle *trans,
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struct btrfs_caching_control *next;
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struct btrfs_caching_control *caching_ctl;
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struct btrfs_block_group_cache *cache;
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struct btrfs_space_info *space_info;
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down_write(&fs_info->commit_root_sem);
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@ -5701,9 +5700,6 @@ void btrfs_prepare_extent_commit(struct btrfs_trans_handle *trans,
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up_write(&fs_info->commit_root_sem);
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list_for_each_entry_rcu(space_info, &fs_info->space_info, list)
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percpu_counter_set(&space_info->total_bytes_pinned, 0);
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update_global_block_rsv(fs_info);
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}
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@ -5741,6 +5737,7 @@ static int unpin_extent_range(struct btrfs_root *root, u64 start, u64 end)
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spin_lock(&cache->lock);
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cache->pinned -= len;
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space_info->bytes_pinned -= len;
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percpu_counter_add(&space_info->total_bytes_pinned, -len);
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if (cache->ro) {
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space_info->bytes_readonly += len;
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readonly = true;
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