Re: [PATCH] btrfs: use BUG() instead of BUG_ON(1)

From: Nikolay Borisov
Date: Mon Mar 25 2019 - 09:06:19 EST



On 25.03.19 Ð. 15:02 Ñ., Arnd Bergmann wrote:
> BUG_ON(1) leads to bogus warnings from clang when
> CONFIG_PROFILE_ANNOTATED_BRANCHES is set:
>
> fs/btrfs/volumes.c:5041:3: error: variable 'max_chunk_size' is used uninitialized whenever 'if' condition is false
> [-Werror,-Wsometimes-uninitialized]
> BUG_ON(1);
> ^~~~~~~~~
> include/asm-generic/bug.h:61:36: note: expanded from macro 'BUG_ON'
> #define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0)
> ^~~~~~~~~~~~~~~~~~~
> include/linux/compiler.h:48:23: note: expanded from macro 'unlikely'
> # define unlikely(x) (__branch_check__(x, 0, __builtin_constant_p(x)))
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> fs/btrfs/volumes.c:5046:9: note: uninitialized use occurs here
> max_chunk_size);
> ^~~~~~~~~~~~~~
> include/linux/kernel.h:860:36: note: expanded from macro 'min'
> #define min(x, y) __careful_cmp(x, y, <)
> ^
> include/linux/kernel.h:853:17: note: expanded from macro '__careful_cmp'
> __cmp_once(x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y), op))
> ^
> include/linux/kernel.h:847:25: note: expanded from macro '__cmp_once'
> typeof(y) unique_y = (y); \
> ^
> fs/btrfs/volumes.c:5041:3: note: remove the 'if' if its condition is always true
> BUG_ON(1);
> ^
> include/asm-generic/bug.h:61:32: note: expanded from macro 'BUG_ON'
> #define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0)
> ^
> fs/btrfs/volumes.c:4993:20: note: initialize the variable 'max_chunk_size' to silence this warning
> u64 max_chunk_size;
> ^
> = 0
>
> Change it to BUG() so clang can see that this code path can never
> continue.

Long-term we have to eliminate to bug_on's but until then:

Reviewed-by: Nikolay Borisov <nborisov@xxxxxxxx>

>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> fs/btrfs/backref.c | 4 ++--
> fs/btrfs/ctree.c | 4 ++--
> fs/btrfs/extent_io.c | 8 ++++----
> fs/btrfs/file.c | 2 +-
> fs/btrfs/inode.c | 2 +-
> fs/btrfs/root-tree.c | 2 +-
> fs/btrfs/volumes.c | 2 +-
> 7 files changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
> index 11459fe84a29..2602072ed906 100644
> --- a/fs/btrfs/backref.c
> +++ b/fs/btrfs/backref.c
> @@ -791,7 +791,7 @@ static int add_delayed_refs(const struct btrfs_fs_info *fs_info,
> count = node->ref_mod * -1;
> break;
> default:
> - BUG_ON(1);
> + BUG();
> }
> *total_refs += count;
> switch (node->type) {
> @@ -1747,7 +1747,7 @@ int extent_from_logical(struct btrfs_fs_info *fs_info, u64 logical,
> else if (flags & BTRFS_EXTENT_FLAG_DATA)
> *flags_ret = BTRFS_EXTENT_FLAG_DATA;
> else
> - BUG_ON(1);
> + BUG();
> return 0;
> }
>
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index 324df36d28bf..75c69829d975 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -4674,7 +4674,7 @@ void btrfs_extend_item(struct btrfs_fs_info *fs_info, struct btrfs_path *path,
> btrfs_print_leaf(leaf);
> btrfs_crit(fs_info, "slot %d too large, nritems %d",
> slot, nritems);
> - BUG_ON(1);
> + BUG();
> }
>
> /*
> @@ -4754,7 +4754,7 @@ void setup_items_for_insert(struct btrfs_root *root, struct btrfs_path *path,
> btrfs_print_leaf(leaf);
> btrfs_crit(fs_info, "slot %d old_data %d data_end %d",
> slot, old_data, data_end);
> - BUG_ON(1);
> + BUG();
> }
> /*
> * item0..itemN ... dataN.offset..dataN.size .. data0.size
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index ca8b8e785cf3..610a98857e22 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -5746,13 +5746,13 @@ void memcpy_extent_buffer(struct extent_buffer *dst, unsigned long dst_offset,
> btrfs_err(fs_info,
> "memmove bogus src_offset %lu move len %lu dst len %lu",
> src_offset, len, dst->len);
> - BUG_ON(1);
> + BUG();
> }
> if (dst_offset + len > dst->len) {
> btrfs_err(fs_info,
> "memmove bogus dst_offset %lu move len %lu dst len %lu",
> dst_offset, len, dst->len);
> - BUG_ON(1);
> + BUG();
> }
>
> while (len > 0) {
> @@ -5793,13 +5793,13 @@ void memmove_extent_buffer(struct extent_buffer *dst, unsigned long dst_offset,
> btrfs_err(fs_info,
> "memmove bogus src_offset %lu move len %lu len %lu",
> src_offset, len, dst->len);
> - BUG_ON(1);
> + BUG();
> }
> if (dst_offset + len > dst->len) {
> btrfs_err(fs_info,
> "memmove bogus dst_offset %lu move len %lu len %lu",
> dst_offset, len, dst->len);
> - BUG_ON(1);
> + BUG();
> }
> if (dst_offset < src_offset) {
> memcpy_extent_buffer(dst, dst_offset, src_offset, len);
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 34fe8a58b0e9..f28aed471693 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1025,7 +1025,7 @@ int __btrfs_drop_extents(struct btrfs_trans_handle *trans,
> continue;
> }
>
> - BUG_ON(1);
> + BUG();
> }
>
> if (!ret && del_nr > 0) {
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 82fdda8ff5ab..98bc66d34e6c 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -1451,7 +1451,7 @@ static noinline int run_delalloc_nocow(struct inode *inode,
> extent_end = ALIGN(extent_end,
> fs_info->sectorsize);
> } else {
> - BUG_ON(1);
> + BUG();
> }
> out_check:
> if (extent_end <= start) {
> diff --git a/fs/btrfs/root-tree.c b/fs/btrfs/root-tree.c
> index 893d12fbfda0..552efc88a016 100644
> --- a/fs/btrfs/root-tree.c
> +++ b/fs/btrfs/root-tree.c
> @@ -141,7 +141,7 @@ int btrfs_update_root(struct btrfs_trans_handle *trans, struct btrfs_root
> btrfs_print_leaf(path->nodes[0]);
> btrfs_crit(fs_info, "unable to update root key %llu %u %llu",
> key->objectid, key->type, key->offset);
> - BUG_ON(1);
> + BUG();
> }
>
> l = path->nodes[0];
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 9024eee889b9..95223fd9f9d0 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -5038,7 +5038,7 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
> } else {
> btrfs_err(info, "invalid chunk type 0x%llx requested",
> type);
> - BUG_ON(1);
> + BUG();
> }
>
> /* We don't want a chunk larger than 10% of writable space */
>