Commit d288db5d authored Jul 02, 2014 by Liu Bo Committed by Chris Mason Jul 03, 2014

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>

parent 130d5b41

fs/btrfs/extent-tree.c

+1 −4

Original line number	Diff line number	Diff line
		@@ -5678,7 +5678,6 @@ void btrfs_prepare_extent_commit(struct btrfs_trans_handle *trans,
		struct btrfs_caching_control *next;
		struct btrfs_caching_control *caching_ctl;
		struct btrfs_block_group_cache *cache;
		struct btrfs_space_info *space_info;

		down_write(&fs_info->commit_root_sem);

		@@ -5701,9 +5700,6 @@ void btrfs_prepare_extent_commit(struct btrfs_trans_handle *trans,

		up_write(&fs_info->commit_root_sem);

		list_for_each_entry_rcu(space_info, &fs_info->space_info, list)
		percpu_counter_set(&space_info->total_bytes_pinned, 0);

		update_global_block_rsv(fs_info);
		}

		@@ -5741,6 +5737,7 @@ static int unpin_extent_range(struct btrfs_root *root, u64 start, u64 end)
		spin_lock(&cache->lock);
		cache->pinned -= len;
		space_info->bytes_pinned -= len;
		percpu_counter_add(&space_info->total_bytes_pinned, -len);
		if (cache->ro) {
		space_info->bytes_readonly += len;
		readonly = true;

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