[ This one is not actually your fault. It's the core code which is
confusing. -dan ]
Hello Qu Wenruo,
The patch b72c3aba09a5: "btrfs: locking: Add extra check in
btrfs_init_new_buffer() to avoid deadlock" from Aug 21, 2018, leads
to the following static checker warning:
fs/btrfs/extent-tree.c:8556 btrfs_init_new_buffer()
warn: possible NULL dereference of 'buf'
fs/btrfs/extent-tree.c
8540 static struct extent_buffer *
8541 btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root,
8542 u64 bytenr, int level, u64 owner)
8543 {
8544 struct btrfs_fs_info *fs_info = root->fs_info;
8545 struct extent_buffer *buf;
8546
8547 buf = btrfs_find_create_tree_block(fs_info, bytenr);
The btrfs_find_create_tree_block() function either returns
alloc_test_extent_buffer() which returns NULL on error or
alloc_extent_buffer() which returns error pointers on error. It
confuses static checkers and me also.
8548 if (IS_ERR(buf))
8549 return buf;
8550
8551 /*
8552 * Extra safety check in case the extent tree is corrupted and extent
8553 * allocator chooses to use a tree block which is already used and
8554 * locked.
8555 */
--> 8556 if (buf->lock_owner == current->pid) {
8557 btrfs_err_rl(fs_info,
8558 "tree block %llu owner %llu already locked by pid=%d, extent tree corruption detected",
8559 buf->start, btrfs_header_owner(buf), current->pid);
8560 free_extent_buffer(buf);
regards,
dan carpenter
