| Message ID | 1421312314-72330-5-git-send-email-borntraeger@de.ibm.com |
|---|---|
| State | New, archived |
| Headers | show |
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 kvm-ppc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 kvm-ppc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 kvm-ppc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 kvm-ppc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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.
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 <borntraeger@de.ibm.com> Cc: Oleg Nesterov <oleg@redhat.com> --- arch/x86/include/asm/spinlock.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)