Re: [PATCH v2 2/2] add check for pointers with __free attribute initialized to NULL

[Joe Perches <joe@perches.com>]

On Fri, 2025-10-24 at 22:59 +0530, Ally Heev wrote:
> pointers with __free attribute initialized to NULL
> pose potential cleanup issues [1] when a function uses
> interdependent variables with cleanup attributes
> 
> Link: https://docs.kernel.org/core-api/cleanup.html [1]
> Link: https://lore.kernel.org/all/68f7b830ec21a_10e910070@dwillia2-mobl4.notmuch/
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Ally Heev <allyheev@gmail.com>
[]
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -7728,6 +7728,12 @@ sub process {
>  			ERROR("UNINITIALIZED_PTR_WITH_FREE",
>  			      "pointer '$1' with __free attribute should be initialized\n" . $herecurr);
>  		}
> +
> +# check for pointers with __free attribute initialized to NULL
> +		while ($line =~ /\*\s*($Ident)\s+$FreeAttribute\s*=\s*NULL\b/g) {
> +			WARN("NULL_INITIALIZED_PTR_WITH_FREE",
> +			      "pointer '$1' with __free attribute should be initialized to a non-NULL address\n" . $herecurr);
> +		}
>  	}

I think this a poor idea as almost all the instances where this
initialization is done are fine.

And there are a lot of them.

$ git grep -P '\b__free\b.*=\s*NULL\s*;' | wc -l
490

And what about these uses that depend on struct path members
.mnt and .dentry being NULL. 

$ git grep -P '\b__free\b.*=\s*\{.*\}\s*;'
fs/configfs/symlink.c:  struct path path __free(path_put) = {};
fs/fhandle.c:   struct path path __free(path_put) = {};
fs/file_attr.c: struct path filepath __free(path_put) = {};
fs/file_attr.c: struct path filepath __free(path_put) = {};
fs/namei.c:     struct path parent_path __free(path_put) = {};
fs/namei.c:     struct path parent_path __free(path_put) = {};
fs/namespace.c: struct path old_path __free(path_put) = {};
fs/namespace.c: struct path path __free(path_put) = {};
fs/namespace.c: struct path old_path __free(path_put) = {};
fs/namespace.c: struct path path __free(path_put) = {};
fs/namespace.c: struct path to_path __free(path_put) = {};
fs/namespace.c: struct path from_path __free(path_put) = {};
fs/namespace.c: struct path new __free(path_put) = {};
fs/namespace.c: struct path old __free(path_put) = {};
fs/namespace.c: struct path root __free(path_put) = {};
fs/namespace.c: struct klistmount kls __free(klistmount_free) = {};
fs/namespace.c: struct path fs_root __free(path_put) = {};
fs/nsfs.c:      struct path path __free(path_put) = {};
fs/nsfs.c:              struct path path __free(path_put) = {};
fs/nsfs.c:      struct path path __free(path_put) = {};
fs/overlayfs/params.c:  struct path layer_path __free(path_put) = {};
fs/overlayfs/params.c:          struct path path __free(path_put) = {};
fs/pidfs.c:     struct path path __free(path_put) = {};
include/linux/path.h: * struct path path __free(path_put) = {};
kernel/acct.c:  struct path internal __free(path_put) = {};     // in that order
kernel/trace/trace_uprobe.c:    struct path path __free(path_put) = {};