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Date:   Mon, 25 Mar 2019 15:06:12 +0200
From:   Nikolay Borisov <nborisov@...e.com>
To:     Arnd Bergmann <arnd@...db.de>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>
Cc:     clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Qu Wenruo <wqu@...e.com>, Liu Bo <bo.liu@...ux.alibaba.com>,
        Filipe Manana <fdmanana@...e.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Anand Jain <Anand.Jain@...cle.com>,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: use BUG() instead of BUG_ON(1)



On 25.03.19 г. 15:02 ч., 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@...e.com>

> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  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 */
> 

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