| Message ID | 20180811160856.24936-1-Eugeniy.Paltsev@synopsys.com |
|---|---|
| State | New |
| Headers | show |
| Series | ARC: atomic64: fix atomic64_add_unless function | expand |
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 <Eugeniy.Paltsev@synopsys.com> 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 <Eugeniy.Paltsev@synopsys.com> > > 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/linux-snps-arc@lists.infradead.org/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" > >
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"
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 <Eugeniy.Paltsev@synopsys.com> --- arch/arc/include/asm/atomic.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)