On 09/24/2013 05:30 PM, Will Deacon wrote:

Hello,

On Sat, Sep 21, 2013 at 12:06:47PM +0100, Chen Gang wrote:

quoted

The return value of atomic64_add_return() is u64 which never less than
zero, so need type cast 's64' for comparing in atomic64_add_negative().

The related error: (allmodconfig for S5PV210, with "EXTRA_CFLAGS=-W"):

  kernel/events/core.c:5404:2: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]


Signed-off-by: Chen Gang <redacted>
---
 arch/arm/include/asm/atomic.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/arm/include/asm/atomic.h b/arch/arm/include/asm/atomic.h
index da1c77d..8cf005d 100644
--- a/arch/arm/include/asm/atomic.h
+++ b/arch/arm/include/asm/atomic.h

@@ -475,7 +475,7 @@ static inline int atomic64_add_unless(atomic64_t *v, u64 a, u64 u)
 	return ret;
 }
 
-#define atomic64_add_negative(a, v)	(atomic64_add_return((a), (v)) < 0)
+#define atomic64_add_negative(a, v)	((s64)atomic64_add_return((a), (v)) < 0)
 #define atomic64_inc(v)			atomic64_add(1LL, (v))
 #define atomic64_inc_return(v)		atomic64_add_return(1LL, (v))
 #define atomic64_inc_and_test(v)	(atomic64_inc_return(v) == 0)

Is this the right fix? It looks more like atomic[64]_t should be signed, but
some 32-bit architectures (ARM, x86, tile) are actually implementing
atomic64_t as u64. Furthermore, there are discrepencies in the operands to
the various atomic64_* function (long long vs u64) which probably need
sorting out.

Since the 32-bit interface is well defined (Documentation/atomic_ops.txt),
I think we should just follow the same signedness rules for the 64-bit
versions.

That sounds reasonable, excluding arm and tile_32, all are defined as
signed (even for related 32-bits functions, arm and tile are also use
signed).

For atomic64_add_negative(), like arm, tile also has the same issue
(unsigned type is never less than zero).

Tomorrow, I will send patch v2 for arm, and another fix patch for tile.
:-)

Thanks.


The related search:

  arm/include/asm/atomic.h:314:static inline u64 atomic64_add_return(u64 i, atomic64_t *v) 
  tile/include/asm/atomic_32.h:123:static inline u64 atomic64_add_return(u64 i, atomic64_t *v) 

  ia64/include/asm/atomic.h:137:#define atomic64_add_return(i,v)                                  \   

  alpha/include/asm/atomic.h:115:static __inline__ long atomic64_add_return(long i, atomic64_t * v)
  arm64/include/asm/atomic.h:194:static inline long atomic64_add_return(long i, atomic64_t *v) 
  frv/include/asm/atomic.h:152:extern long long atomic64_add_return(long long i, atomic64_t *v);
  mips/include/asm/atomic.h:499:static __inline__ long atomic64_add_return(long i, atomic64_t * v)
  parisc/include/asm/atomic.h:156:__atomic64_add_return(s64 i, atomic64_t *v) 
  parisc/include/asm/atomic.h:190:#define atomic64_add_return(i,v)        (__atomic64_add_return( ((s64)(i)),(v)))
  powerpc/include/asm/atomic.h:310:static __inline__ long atomic64_add_return(long a, atomic64_t *v) 
  s390/include/asm/atomic.h:199:static inline long long atomic64_add_return(long long i, atomic64_t *v) 
  s390/include/asm/atomic.h:284:static inline long long atomic64_add_return(long long i, atomic64_t *v) 
  sparc/include/asm/atomic_64.h:42:#define atomic64_add_return(i, v) atomic64_add_ret(i, v)
  tile/include/asm/atomic_64.h:73:static inline long atomic64_add_return(long i, atomic64_t *v) 
  x86/include/asm/atomic64_32.h:134:static inline long long atomic64_add_return(long long i, atomic64_t *v) 
  x86/include/asm/atomic64_64.h:171:static inline long atomic64_add_return(long i, atomic64_t *v) 

Will

Thanks
-- 
Chen Gang