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Btrfs: clarify do_chunk_alloc()'s return value

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Function start_transaction() can return ERR_PTR(1) when flush is
BTRFS_RESERVE_FLUSH_LIMIT, so the call graph is

start_transaction (return ERR_PTR(1))
  -> btrfs_block_rsv_add (return 1)
     -> reserve_metadata_bytes (return 1)
        -> flush_space (return 1)
           -> do_chunk_alloc  (return 1)

With BTRFS_RESERVE_FLUSH_LIMIT, if flush_space is already on the
flush_state of ALLOC_CHUNK and it successfully allocates a new
chunk, then instead of trying to reserve space again,
reserve_metadata_bytes returns 1 immediately.

Eventually the callers who call start_transaction() usually just
do the IS_ERR() check which ERR_PTR(1) can pass, then it'll get
a panic when dereferencing a pointer which is ERR_PTR(1).

The following patch fixes the above problem.
"btrfs: flush_space: treat return value of do_chunk_alloc properly"
https://patchwork.kernel.org/patch/7778651/

This add comments to clarify do_chunk_alloc()'s return value.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
This commit is contained in:
Liu Bo 2016-07-29 11:09:50 -07:00 committed by Chris Mason
parent 9e7cc91a6d
commit 28b737f6ed
1 changed files with 9 additions and 0 deletions
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9
fs/btrfs/extent-tree.c
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@ -4457,6 +4457,15 @@ void check_system_chunk(struct btrfs_trans_handle *trans,
}
}
/*
* If force is CHUNK_ALLOC_FORCE:
* - return 1 if it successfully allocates a chunk,
* - return errors including -ENOSPC otherwise.
* If force is NOT CHUNK_ALLOC_FORCE:
* - return 0 if it doesn't need to allocate a new chunk,
* - return 1 if it successfully allocates a chunk,
* - return errors including -ENOSPC otherwise.
*/
static int do_chunk_alloc(struct btrfs_trans_handle *trans,
struct btrfs_root *extent_root, u64 flags, int force)
{