From 28b737f6ede3661fe610937706c4a6f50e9ab769 Mon Sep 17 00:00:00 2001 From: Liu Bo Date: Fri, 29 Jul 2016 11:09:50 -0700 Subject: [PATCH] Btrfs: clarify do_chunk_alloc()'s return value 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 Signed-off-by: David Sterba Signed-off-by: Chris Mason --- fs/btrfs/extent-tree.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 133c93b..d5d3cfb 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -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) { -- 2.7.4