Re: [PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE->READ_ONCE
Am 15.01.2015 um 21:01 schrieb Oleg Nesterov:
> On 01/15, Christian Borntraeger wrote:
>>
>> Am 15.01.2015 um 20:38 schrieb Oleg Nesterov:
>>> On 01/15, Christian Borntraeger wrote:
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -186,7 +186,7 @@ static inline void
arch_spin_unlock_wait(arch_spinlock_t *lock)
__ticket_t head = ACCESS_ONCE(lock->tickets.head);
for (;;) {
- struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
+ struct __raw_tickets tmp = READ_ONCE(lock->tickets);
>>>
>>> Agreed, but what about another ACCESS_ONCE() above?
>>>
>>> Oleg.
>>
>> tickets.head is a scalar type, so ACCESS_ONCE does work fine with gcc
>> 4.6/4.7.
>> My goal was to convert all accesses on non-scalar types
>
> I understand, but READ_ONCE(lock->tickets.head) looks better anyway and
> arch_spin_lock() already use READ_ONCE() for this.
>
> So why we should keep the last ACCESS_ONCE() in spinlock.h ? Just to make
> another cosmetic cleanup which touches the same function later?
OK, I will change that one as well.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE->READ_ONCE
On 01/15, Christian Borntraeger wrote:
>
> Am 15.01.2015 um 20:38 schrieb Oleg Nesterov:
> > On 01/15, Christian Borntraeger wrote:
> >>
> >> --- a/arch/x86/include/asm/spinlock.h
> >> +++ b/arch/x86/include/asm/spinlock.h
> >> @@ -186,7 +186,7 @@ static inline void
> >> arch_spin_unlock_wait(arch_spinlock_t *lock)
> >>__ticket_t head = ACCESS_ONCE(lock->tickets.head);
> >>
> >>for (;;) {
> >> - struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
> >> + struct __raw_tickets tmp = READ_ONCE(lock->tickets);
> >
> > Agreed, but what about another ACCESS_ONCE() above?
> >
> > Oleg.
>
> tickets.head is a scalar type, so ACCESS_ONCE does work fine with gcc 4.6/4.7.
> My goal was to convert all accesses on non-scalar types
I understand, but READ_ONCE(lock->tickets.head) looks better anyway and
arch_spin_lock() already use READ_ONCE() for this.
So why we should keep the last ACCESS_ONCE() in spinlock.h ? Just to make
another cosmetic cleanup which touches the same function later?
Oleg.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE->READ_ONCE
Am 15.01.2015 um 20:38 schrieb Oleg Nesterov:
> On 01/15, Christian Borntraeger wrote:
>>
>> --- a/arch/x86/include/asm/spinlock.h
>> +++ b/arch/x86/include/asm/spinlock.h
>> @@ -186,7 +186,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t
>> *lock)
>> __ticket_t head = ACCESS_ONCE(lock->tickets.head);
>>
>> for (;;) {
>> -struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
>> +struct __raw_tickets tmp = READ_ONCE(lock->tickets);
>
> Agreed, but what about another ACCESS_ONCE() above?
>
> Oleg.
>
tickets.head is a scalar type, so ACCESS_ONCE does work fine with gcc 4.6/4.7.
My goal was to convert all accesses on non-scalar types as until
"kernel: tighten rules for ACCESS ONCE" is merged because anything else would be
a Whac-a-mole like adventure (I learned that during the last round in next: all
conversions in this series fix up changes made during this merge window)
We probably going to do a bigger bunch of bulk conversion later on when
"kernel: tighten rules for ACCESS ONCE" prevents new problems.
Makes sense?
Christian
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE->READ_ONCE
On 01/15, Christian Borntraeger wrote:
>
> --- a/arch/x86/include/asm/spinlock.h
> +++ b/arch/x86/include/asm/spinlock.h
> @@ -186,7 +186,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t
> *lock)
> __ticket_t head = ACCESS_ONCE(lock->tickets.head);
>
> for (;;) {
> - struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
> + struct __raw_tickets tmp = READ_ONCE(lock->tickets);
Agreed, but what about another ACCESS_ONCE() above?
Oleg.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE->READ_ONCE
commit 78bff1c8684f ("x86/ticketlock: Fix spin_unlock_wait() livelock")
introduced another ACCESS_ONCE case in x86 spinlock.h.
Change that as well.
Signed-off-by: Christian Borntraeger
Cc: Oleg Nesterov
---
arch/x86/include/asm/spinlock.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 625660f..9264f0f 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -186,7 +186,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t
*lock)
__ticket_t head = ACCESS_ONCE(lock->tickets.head);
for (;;) {
- struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
+ struct __raw_tickets tmp = READ_ONCE(lock->tickets);
/*
* We need to check "unlocked" in a loop, tmp.head == head
* can be false positive because of overflow.
--
1.9.3
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE-READ_ONCE
Am 15.01.2015 um 20:38 schrieb Oleg Nesterov:
On 01/15, Christian Borntraeger wrote:
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -186,7 +186,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t
*lock)
__ticket_t head = ACCESS_ONCE(lock-tickets.head);
for (;;) {
-struct __raw_tickets tmp = ACCESS_ONCE(lock-tickets);
+struct __raw_tickets tmp = READ_ONCE(lock-tickets);
Agreed, but what about another ACCESS_ONCE() above?
Oleg.
tickets.head is a scalar type, so ACCESS_ONCE does work fine with gcc 4.6/4.7.
My goal was to convert all accesses on non-scalar types as until
kernel: tighten rules for ACCESS ONCE is merged because anything else would be
a Whac-a-mole like adventure (I learned that during the last round in next: all
conversions in this series fix up changes made during this merge window)
We probably going to do a bigger bunch of bulk conversion later on when
kernel: tighten rules for ACCESS ONCE prevents new problems.
Makes sense?
Christian
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE-READ_ONCE
On 01/15, Christian Borntraeger wrote:
Am 15.01.2015 um 20:38 schrieb Oleg Nesterov:
On 01/15, Christian Borntraeger wrote:
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -186,7 +186,7 @@ static inline void
arch_spin_unlock_wait(arch_spinlock_t *lock)
__ticket_t head = ACCESS_ONCE(lock-tickets.head);
for (;;) {
- struct __raw_tickets tmp = ACCESS_ONCE(lock-tickets);
+ struct __raw_tickets tmp = READ_ONCE(lock-tickets);
Agreed, but what about another ACCESS_ONCE() above?
Oleg.
tickets.head is a scalar type, so ACCESS_ONCE does work fine with gcc 4.6/4.7.
My goal was to convert all accesses on non-scalar types
I understand, but READ_ONCE(lock-tickets.head) looks better anyway and
arch_spin_lock() already use READ_ONCE() for this.
So why we should keep the last ACCESS_ONCE() in spinlock.h ? Just to make
another cosmetic cleanup which touches the same function later?
Oleg.
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE-READ_ONCE
On 01/15, Christian Borntraeger wrote:
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -186,7 +186,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t
*lock)
__ticket_t head = ACCESS_ONCE(lock-tickets.head);
for (;;) {
- struct __raw_tickets tmp = ACCESS_ONCE(lock-tickets);
+ struct __raw_tickets tmp = READ_ONCE(lock-tickets);
Agreed, but what about another ACCESS_ONCE() above?
Oleg.
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE-READ_ONCE
Am 15.01.2015 um 21:01 schrieb Oleg Nesterov:
On 01/15, Christian Borntraeger wrote:
Am 15.01.2015 um 20:38 schrieb Oleg Nesterov:
On 01/15, Christian Borntraeger wrote:
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -186,7 +186,7 @@ static inline void
arch_spin_unlock_wait(arch_spinlock_t *lock)
__ticket_t head = ACCESS_ONCE(lock-tickets.head);
for (;;) {
- struct __raw_tickets tmp = ACCESS_ONCE(lock-tickets);
+ struct __raw_tickets tmp = READ_ONCE(lock-tickets);
Agreed, but what about another ACCESS_ONCE() above?
Oleg.
tickets.head is a scalar type, so ACCESS_ONCE does work fine with gcc
4.6/4.7.
My goal was to convert all accesses on non-scalar types
I understand, but READ_ONCE(lock-tickets.head) looks better anyway and
arch_spin_lock() already use READ_ONCE() for this.
So why we should keep the last ACCESS_ONCE() in spinlock.h ? Just to make
another cosmetic cleanup which touches the same function later?
OK, I will change that one as well.
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[PATCH 4/8] x86/spinlock: Leftover conversion ACCESS_ONCE-READ_ONCE
commit 78bff1c8684f (x86/ticketlock: Fix spin_unlock_wait() livelock)
introduced another ACCESS_ONCE case in x86 spinlock.h.
Change that as well.
Signed-off-by: Christian Borntraeger borntrae...@de.ibm.com
Cc: Oleg Nesterov o...@redhat.com
---
arch/x86/include/asm/spinlock.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 625660f..9264f0f 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -186,7 +186,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t
*lock)
__ticket_t head = ACCESS_ONCE(lock-tickets.head);
for (;;) {
- struct __raw_tickets tmp = ACCESS_ONCE(lock-tickets);
+ struct __raw_tickets tmp = READ_ONCE(lock-tickets);
/*
* We need to check unlocked in a loop, tmp.head == head
* can be false positive because of overflow.
--
1.9.3
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
