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authorLiu Bo <bo.li.liu@oracle.com>2016-07-29 11:09:50 -0700
committerChris Mason <clm@fb.com>2016-08-25 03:58:27 -0700
commit28b737f6ede3661fe610937706c4a6f50e9ab769 (patch)
parent9e7cc91a6d18a4973c6d2cc104871439c9e94f3d (diff)
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 <bo.li.liu@oracle.com> Signed-off-by: David Sterba <dsterba@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
1 files changed, 9 insertions, 0 deletions
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 133c93b0a0f1..d5d3cfb1f66f 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)