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https://github.com/kdave/btrfs-progs
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btrfs-progs: Avoid nested chunk allocation call
There is a indirect recursion which can reach the extent reservation: btrfs_reserve_extent() <--| |- do_chunk_alloc() | |- btrfs_alloc_chunk() | |- btrfs_insert_item() | |- btrfs_reserve_extent() <--| Currently, we're using root->ref_cows to determine whether we should do chunk prealloc to avoid such loop. But that's still a hidden trap. Instead of solving it using some hidden tricks, this patch will make chunk/block group allocation exclusive. Now if do_chunk_alloc() determines to alloc chunk, it will set a flag in transaction handle so new call of do_chunk_alloc() will refuse to allocate new chunk until current chunk allocation finishes. The chunks get over-allocated by 2M so there's enough space in case the recursive call asks for a different type of blockgroup. Signed-off-by: Qu Wenruo <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
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@ -1717,10 +1717,20 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans,
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(flags & BTRFS_BLOCK_GROUP_SYSTEM))
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return 0;
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/*
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* We're going to allocate new chunk, during the process, we will
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* allocate new tree blocks, which can trigger new chunk allocation
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* again. Avoid the recursion.
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*/
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if (trans->allocating_chunk)
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return 0;
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trans->allocating_chunk = 1;
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ret = btrfs_alloc_chunk(trans, fs_info, &start, &num_bytes,
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space_info->flags);
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if (ret == -ENOSPC) {
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space_info->full = 1;
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trans->allocating_chunk = 0;
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return 0;
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}
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@ -1729,6 +1739,7 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans,
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ret = btrfs_make_block_group(trans, fs_info, 0, space_info->flags,
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start, num_bytes);
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BUG_ON(ret);
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trans->allocating_chunk = 0;
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return 0;
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}
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@ -48,6 +48,7 @@ struct btrfs_trans_handle* btrfs_start_transaction(struct btrfs_root *root,
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h->transid = fs_info->generation;
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h->blocks_reserved = num_blocks;
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h->reinit_extent_tree = false;
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h->allocating_chunk = 0;
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root->last_trans = h->transid;
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root->commit_root = root->node;
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extent_buffer_get(root->node);
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@ -29,6 +29,7 @@ struct btrfs_trans_handle {
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u64 alloc_exclude_start;
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u64 alloc_exclude_nr;
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bool reinit_extent_tree;
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unsigned int allocating_chunk:1;
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u64 delayed_ref_updates;
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unsigned long blocks_reserved;
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unsigned long blocks_used;
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