[PATCH] err.h: add __must_check to error pointer handlers

[PATCH] err.h: add __must_check to error pointer handlers

[Jani Nikula]

Add __must_check to error pointer handlers to have the compiler warn
about mistakes like:

	if (err)
		ERR_PTR(err);

Signed-off-by: Jani Nikula <ext-jani.1.nikula@nokia.com>
---
 include/linux/err.h |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/err.h b/include/linux/err.h
index 1b12642..448afc1 100644
--- a/include/linux/err.h
+++ b/include/linux/err.h
@@ -19,22 +19,22 @@
 
 #define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO)
 
-static inline void *ERR_PTR(long error)
+static inline void * __must_check ERR_PTR(long error)
 {
 	return (void *) error;
 }
 
-static inline long PTR_ERR(const void *ptr)
+static inline long __must_check PTR_ERR(const void *ptr)
 {
 	return (long) ptr;
 }
 
-static inline long IS_ERR(const void *ptr)
+static inline long __must_check IS_ERR(const void *ptr)
 {
 	return IS_ERR_VALUE((unsigned long)ptr);
 }
 
-static inline long IS_ERR_OR_NULL(const void *ptr)
+static inline long __must_check IS_ERR_OR_NULL(const void *ptr)
 {
 	return !ptr || IS_ERR_VALUE((unsigned long)ptr);
 }
@@ -46,7 +46,7 @@ static inline long IS_ERR_OR_NULL(const void *ptr)
  * Explicitly cast an error-valued pointer to another pointer type in such a
  * way as to make it clear that's what's going on.
  */
-static inline void *ERR_CAST(const void *ptr)
+static inline void * __must_check ERR_CAST(const void *ptr)
 {
 	/* cast away the const */
 	return (void *) ptr;
-- 
1.6.5.2

Re: [PATCH] err.h: add __must_check to error pointer handlers

[Alexey Dobriyan]

On Fri, Mar 12, 2010 at 03:45:40PM +0200, Jani Nikula wrote:
> Add __must_check to error pointer handlers to have the compiler warn
> about mistakes like:
> 
> 	if (err)
> 		ERR_PTR(err);

> -static inline void *ERR_PTR(long error)
> +static inline void * __must_check ERR_PTR(long error)

We had bugs like that?

Pretty much every non-void function should be marked then.

Re: [PATCH] err.h: add __must_check to error pointer handlers

[Phil Carmody]

On 12/03/10 19:40 +0100, ext Alexey Dobriyan wrote:
> On Fri, Mar 12, 2010 at 03:45:40PM +0200, Jani Nikula wrote:
> > Add __must_check to error pointer handlers to have the compiler warn
> > about mistakes like:
> > 
> > 	if (err)
> > 		ERR_PTR(err);
> 
> > -static inline void *ERR_PTR(long error)
> > +static inline void * __must_check ERR_PTR(long error)
> 
> We had bugs like that?

Two popped out immediately. Patches have been sent to appropriate
maintainers. Grepping my inbox:

Mar 12 Nikula Jani [PATCH] enclosure: fix error path - actually return ERR_PTR() on error
Mar 12 Nikula Jani [PATCH] sunrpc: fix error path - actually return ERR_PTR() on error

There's a slim chance that there may be others (grep doesn't find any
more obvious ones), but as allmodconfig seems broken currently, there
may be others which are as yet undiscovered. 

> Pretty much every non-void function should be marked then.

All functions where it makes no sense ignore the return value. You
really wouldn't be doing an ERR_PTR unless you wanted to use the result.

Note that __must_check doesn't actually require 'checking', merely
'using' the return value, which includes just storing it in a variable,
and then later ignoring it.

An alternative static code analysis method could be used to detect such 
things. Coverity Prevent uses a heuristic algorithm to detect missing 
checks of return values using a popularity contest. Most people check 
it - then everyone should probably check it.

Phil