Current implementation of 'atomic64_add_unless' function
(and hence 'atomic64_inc_not_zero') return incorrect value
if lover 32 bits of compared 64-bit number are equal and
higher 32 bits aren't.
For in following example atomic64_add_unless must return '1'
but it actually returns '0':
--------->8---------
atomic64_t val = ATOMIC64_INIT(0x4444000000000000LL);
int ret = atomic64_add_unless(&val, 1LL, 0LL)
--------->8---------
This happens because we write '0' to returned variable regardless
of higher 32 bits comparison result.
So fix it.
NOTE:
this change was tested with atomic64_test.
Signed-off-by: Eugeniy Paltsev <[email protected]>
---
arch/arc/include/asm/atomic.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arc/include/asm/atomic.h b/arch/arc/include/asm/atomic.h
index 11859287c52a..e840cb1763b2 100644
--- a/arch/arc/include/asm/atomic.h
+++ b/arch/arc/include/asm/atomic.h
@@ -578,11 +578,11 @@ static inline int atomic64_add_unless(atomic64_t *v, long long a, long long u)
__asm__ __volatile__(
"1: llockd %0, [%2] \n"
- " mov %1, 1 \n"
" brne %L0, %L4, 2f # continue to add since v != u \n"
" breq.d %H0, %H4, 3f # return since v == u \n"
" mov %1, 0 \n"
"2: \n"
+ " mov %1, 1 \n"
" add.f %L0, %L0, %L3 \n"
" adc %H0, %H0, %H3 \n"
" scondd %0, [%2] \n"
--
2.14.4
On 08/11/2018 09:09 AM, Eugeniy Paltsev wrote:
> Current implementation of 'atomic64_add_unless' function
> (and hence 'atomic64_inc_not_zero') return incorrect value
> if lover 32 bits of compared 64-bit number are equal and
> higher 32 bits aren't.
>
> For in following example atomic64_add_unless must return '1'
> but it actually returns '0':
> --------->8---------
> atomic64_t val = ATOMIC64_INIT(0x4444000000000000LL);
> int ret = atomic64_add_unless(&val, 1LL, 0LL)
> --------->8---------
>
> This happens because we write '0' to returned variable regardless
> of higher 32 bits comparison result.
>
> So fix it.
>
> NOTE:
> this change was tested with atomic64_test.
>
> Signed-off-by: Eugeniy Paltsev <[email protected]>
LGTM. Curious, was this from code review or did u actually run into this ?
Thx,
-Vineet
> ---
> arch/arc/include/asm/atomic.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arc/include/asm/atomic.h b/arch/arc/include/asm/atomic.h
> index 11859287c52a..e840cb1763b2 100644
> --- a/arch/arc/include/asm/atomic.h
> +++ b/arch/arc/include/asm/atomic.h
> @@ -578,11 +578,11 @@ static inline int atomic64_add_unless(atomic64_t *v, long long a, long long u)
>
> __asm__ __volatile__(
> "1: llockd %0, [%2] \n"
> - " mov %1, 1 \n"
> " brne %L0, %L4, 2f # continue to add since v != u \n"
> " breq.d %H0, %H4, 3f # return since v == u \n"
> " mov %1, 0 \n"
> "2: \n"
> + " mov %1, 1 \n"
> " add.f %L0, %L0, %L3 \n"
> " adc %H0, %H0, %H3 \n"
> " scondd %0, [%2] \n"
On Tue, 2018-08-14 at 13:42 +0000, Vineet Gupta wrote:
> On 08/11/2018 09:09 AM, Eugeniy Paltsev wrote:
> > Current implementation of 'atomic64_add_unless' function
> > (and hence 'atomic64_inc_not_zero') return incorrect value
> > if lover 32 bits of compared 64-bit number are equal and
> > higher 32 bits aren't.
> >
> > For in following example atomic64_add_unless must return '1'
> > but it actually returns '0':
> > --------->8---------
> > atomic64_t val = ATOMIC64_INIT(0x4444000000000000LL);
> > int ret = atomic64_add_unless(&val, 1LL, 0LL)
> > --------->8---------
> >
> > This happens because we write '0' to returned variable regardless
> > of higher 32 bits comparison result.
> >
> > So fix it.
> >
> > NOTE:
> > this change was tested with atomic64_test.
> >
> > Signed-off-by: Eugeniy Paltsev <[email protected]>
>
> LGTM. Curious, was this from code review or did u actually run into this ?
I've accidentally run into this when I played with atomic64_* functions
trying to implement hack to automatically align LL64/SC64 data for atomic 64-bit
operations on ARC to avoid problems like:
https://www.mail-archive.com/[email protected]/msg03791.html
> Thx,
> -Vineet
>
> > ---
> > arch/arc/include/asm/atomic.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arc/include/asm/atomic.h b/arch/arc/include/asm/atomic.h
> > index 11859287c52a..e840cb1763b2 100644
> > --- a/arch/arc/include/asm/atomic.h
> > +++ b/arch/arc/include/asm/atomic.h
> > @@ -578,11 +578,11 @@ static inline int atomic64_add_unless(atomic64_t *v, long long a, long long u)
> >
> > __asm__ __volatile__(
> > "1: llockd %0, [%2] \n"
> > - " mov %1, 1 \n"
> > " brne %L0, %L4, 2f # continue to add since v != u \n"
> > " breq.d %H0, %H4, 3f # return since v == u \n"
> > " mov %1, 0 \n"
> > "2: \n"
> > + " mov %1, 1 \n"
> > " add.f %L0, %L0, %L3 \n"
> > " adc %H0, %H0, %H3 \n"
> > " scondd %0, [%2] \n"
>
>
--
Eugeniy Paltsev