Re: [PATCH] ERR_PTR: warn when ERR_PTR parameter is valid argument

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 22 May 2008 18:50:19 +0200
Marcin Slusarz <marcin.slusarz@gmail.com> wrote:

> Check at runtime whether error argument of ERR_PTR is valid.
> It can catch bugs which possibly lead to oops or panic earlier.
> 
> Currently there are > 600 calls of ERR_PTR with non-constant argument.
> 
> Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Al Viro <viro@ZenIV.linux.org.uk>
> Cc: Alexey Dobriyan <adobriyan@gmail.com>
> Cc: Johannes Weiner <hannes@saeurebad.de>
> ---
>  include/linux/err.h |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/err.h b/include/linux/err.h
> index 4773ed3..f7e098e 100644
> --- a/include/linux/err.h
> +++ b/include/linux/err.h
> @@ -3,6 +3,7 @@
>  
>  #include <linux/compiler.h>
>  
> +#include <asm/bug.h>
>  #include <asm/errno.h>
>  
>  /*
> @@ -22,6 +23,7 @@
>  
>  static inline void *__ERR_PTR(long error)
>  {
> +	WARN_ON(!VALID_ERR_PTR_ARG(error));
>  	return (void *) error;
>  }

It would be regrettable to add source-level complexity and runtime cost
to detect this particular bug.  I think it would be better to do this
via static source-code checking if at all possible.

Is there _any_ legitimate use of non-negative EFOO?  There might be
some baroque bits of code which are using non-negative constants in a
non-buggy fashion, but I bet they could be reworked to use negative
constants.

In which case I'd have thought that a script which

a) extracts all the EFOO identifiers from include/*/errno.h and

b) greps the tree for non-negative uses of those

would have 100% coverage?

We might need to touch up some code sites to avoid triggering false
positives and make that script's life a bit easier, but that's fine.