[PATCH][RFC] err.h: silence sparse warning: dereference of noderef expression

[PATCH][RFC] err.h: silence sparse warning: dereference of noderef expression

[Jeff Layton]

From: Jeff Layton <jlayton@primarydata.com>

Lately, when I do a make with C=1, I get *tons* of these warnings:

    include/linux/err.h:35:16: warning: dereference of noderef expression
    include/linux/err.h:30:23: warning: dereference of noderef expression

...so many that it's really driven down the signal to noise ratio. I've
taken a look at what's driving these warnings and I really just don't
get it. The pointers being passed in aren't being dereferenced as far
as I can tell, so what is sparse complaining about?

Even odder, just in playing around I've noticed that removing the
__force directives seems to silence these warnings. This is really
strange since all of the docs I see indicate that __force is supposed to
help silence sparse warnings, not cause them.

This patch just removes the __force directives on the err.h inlines and
that silences the warnings for me. Dan originally added those in commit
e7152b97f38f1 (err.h: IS_ERR() can accept __user pointers).

I don't really consider this a serious proposal for inclusion, but
rather just a starting point for discussion. What's the right way to fix
this problem? Is this a bug in sparse?

Signed-off-by: Jeff Layton <jlayton@primarydata.com>
---
 include/linux/err.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/err.h b/include/linux/err.h
index a729120644d5..284897f403b3 100644
--- a/include/linux/err.h
+++ b/include/linux/err.h
@@ -25,17 +25,17 @@ static inline void * __must_check ERR_PTR(long error)
 	return (void *) error;
 }
 
-static inline long __must_check PTR_ERR(__force const void *ptr)
+static inline long __must_check PTR_ERR(const void *ptr)
 {
 	return (long) ptr;
 }
 
-static inline bool __must_check IS_ERR(__force const void *ptr)
+static inline bool __must_check IS_ERR(const void *ptr)
 {
 	return IS_ERR_VALUE((unsigned long)ptr);
 }
 
-static inline bool __must_check IS_ERR_OR_NULL(__force const void *ptr)
+static inline bool __must_check IS_ERR_OR_NULL(const void *ptr)
 {
 	return !ptr || IS_ERR_VALUE((unsigned long)ptr);
 }
@@ -47,13 +47,13 @@ static inline bool __must_check IS_ERR_OR_NULL(__force 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 * __must_check ERR_CAST(__force const void *ptr)
+static inline void * __must_check ERR_CAST(const void *ptr)
 {
 	/* cast away the const */
 	return (void *) ptr;
 }
 
-static inline int __must_check PTR_ERR_OR_ZERO(__force const void *ptr)
+static inline int __must_check PTR_ERR_OR_ZERO(const void *ptr)
 {
 	if (IS_ERR(ptr))
 		return PTR_ERR(ptr);
-- 
1.9.3

Re: [PATCH][RFC] err.h: silence sparse warning: dereference of noderef expression

[Dan Carpenter]

On Tue, Jun 10, 2014 at 05:38:49PM -0400, Jeff Layton wrote:
> From: Jeff Layton <jlayton@primarydata.com>
> 
> Lately, when I do a make with C=1, I get *tons* of these warnings:
> 
>     include/linux/err.h:35:16: warning: dereference of noderef expression
>     include/linux/err.h:30:23: warning: dereference of noderef expression

Which version of Sparse, which version of the kernel and which .c file
can I compile to reproduce this?

I built fs/cifs/ and I didn't see the sparse warning.

regards,
dan carpenter

Re: [PATCH][RFC] err.h: silence sparse warning: dereference of noderef expression

[Jeff Layton]

On Wed, 11 Jun 2014 08:45:18 +0300
Dan Carpenter <dan.carpenter@oracle.com> wrote:

> On Tue, Jun 10, 2014 at 05:38:49PM -0400, Jeff Layton wrote:
> > From: Jeff Layton <jlayton@primarydata.com>
> > 
> > Lately, when I do a make with C=1, I get *tons* of these warnings:
> > 
> >     include/linux/err.h:35:16: warning: dereference of noderef expression
> >     include/linux/err.h:30:23: warning: dereference of noderef expression
> 
> Which version of Sparse, which version of the kernel and which .c file
> can I compile to reproduce this?
> 
> I built fs/cifs/ and I didn't see the sparse warning.
> 
> regards,
> dan carpenter
> 

$ rpm -q sparse
sparse-0.5.0-1.fc20.x86_64

I see it all over the tree, but an easy example is fs/locks.c:

$ make fs/locks.o C=1
make[1]: Nothing to be done for `all'.
make[1]: Nothing to be done for `relocs'.
  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  CALL    scripts/checksyscalls.sh
  CHECK   fs/locks.c
include/linux/err.h:35:16: warning: dereference of noderef expression
include/linux/err.h:30:23: warning: dereference of noderef expression
include/linux/err.h:35:16: warning: dereference of noderef expression
include/linux/err.h:30:23: warning: dereference of noderef expression
  CC      fs/locks.o

It has two IS_ERR calls and two PTR_ERR calls, and each generates the
warning.

-- 
Jeff Layton <jlayton@poochiereds.net>

Re: [PATCH][RFC] err.h: silence sparse warning: dereference of noderef expression

[Dan Carpenter]

On Wed, Jun 11, 2014 at 07:06:32AM -0400, Jeff Layton wrote:
> $ rpm -q sparse
> sparse-0.5.0-1.fc20.x86_64
>
> I see it all over the tree, but an easy example is fs/locks.c:
> 
> $ make fs/locks.o C=1
> make[1]: Nothing to be done for `all'.
> make[1]: Nothing to be done for `relocs'.
>   CHK     include/config/kernel.release
>   CHK     include/generated/uapi/linux/version.h
>   CHK     include/generated/utsrelease.h
>   CALL    scripts/checksyscalls.sh
>   CHECK   fs/locks.c
> include/linux/err.h:35:16: warning: dereference of noderef expression
> include/linux/err.h:30:23: warning: dereference of noderef expression
> include/linux/err.h:35:16: warning: dereference of noderef expression
> include/linux/err.h:30:23: warning: dereference of noderef expression
>   CC      fs/locks.o
> 
> It has two IS_ERR calls and two PTR_ERR calls, and each generates the
> warning.
>

I downloaded the Fedora SRPM and built the binary but I still wasn't
able to reproduce the bug.

dcarpenter@speke:~/progs/kernel/devel$ /tmp/sparse/sparse-0.5.0/sparse --version
0.5.0
dcarpenter@speke:~/progs/kernel/devel$ make C=2 CHECK=/tmp/sparse/sparse-0.5.0/sparse fs/locks.o
  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  CALL    scripts/checksyscalls.sh
<stdin>:1226:2: warning: #warning syscall finit_module not implemented [-Wcpp]
<stdin>:1229:2: warning: #warning syscall sched_setattr not implemented [-Wcpp]
<stdin>:1232:2: warning: #warning syscall sched_getattr not implemented [-Wcpp]
<stdin>:1235:2: warning: #warning syscall renameat2 not implemented [-Wcpp]
  CHECK   scripts/mod/empty.c
  CHECK   fs/locks.c
dcarpenter@speke:~/progs/kernel/devel$

I'm on today's linux-next.  I can't think of a kernel configuration
issue which would cause this...

regards,
dan carpenter

Re: [PATCH][RFC] err.h: silence sparse warning: dereference of noderef expression

[Jeff Layton]

On Wed, 11 Jun 2014 16:11:46 +0300
Dan Carpenter <dan.carpenter@oracle.com> wrote:

> On Wed, Jun 11, 2014 at 07:06:32AM -0400, Jeff Layton wrote:
> > $ rpm -q sparse
> > sparse-0.5.0-1.fc20.x86_64
> >
> > I see it all over the tree, but an easy example is fs/locks.c:
> > 
> > $ make fs/locks.o C=1
> > make[1]: Nothing to be done for `all'.
> > make[1]: Nothing to be done for `relocs'.
> >   CHK     include/config/kernel.release
> >   CHK     include/generated/uapi/linux/version.h
> >   CHK     include/generated/utsrelease.h
> >   CALL    scripts/checksyscalls.sh
> >   CHECK   fs/locks.c
> > include/linux/err.h:35:16: warning: dereference of noderef expression
> > include/linux/err.h:30:23: warning: dereference of noderef expression
> > include/linux/err.h:35:16: warning: dereference of noderef expression
> > include/linux/err.h:30:23: warning: dereference of noderef expression
> >   CC      fs/locks.o
> > 
> > It has two IS_ERR calls and two PTR_ERR calls, and each generates the
> > warning.
> >
> 
> I downloaded the Fedora SRPM and built the binary but I still wasn't
> able to reproduce the bug.
> 
> dcarpenter@speke:~/progs/kernel/devel$ /tmp/sparse/sparse-0.5.0/sparse --version
> 0.5.0
> dcarpenter@speke:~/progs/kernel/devel$ make C=2 CHECK=/tmp/sparse/sparse-0.5.0/sparse fs/locks.o
>   CHK     include/config/kernel.release
>   CHK     include/generated/uapi/linux/version.h
>   CHK     include/generated/utsrelease.h
>   CALL    scripts/checksyscalls.sh
> <stdin>:1226:2: warning: #warning syscall finit_module not implemented [-Wcpp]
> <stdin>:1229:2: warning: #warning syscall sched_setattr not implemented [-Wcpp]
> <stdin>:1232:2: warning: #warning syscall sched_getattr not implemented [-Wcpp]
> <stdin>:1235:2: warning: #warning syscall renameat2 not implemented [-Wcpp]
>   CHECK   scripts/mod/empty.c
>   CHECK   fs/locks.c
> dcarpenter@speke:~/progs/kernel/devel$
> 
> I'm on today's linux-next.  I can't think of a kernel configuration
> issue which would cause this...
> 
> regards,
> dan carpenter

Could it be arch-specific then? What arch are you using? I'm on x86_64.
I know that quite a few other people have mentioned seeing these
warnings as well, so I'm pretty sure it's not just me.

-- 
Jeff Layton <jlayton@poochiereds.net>