Messages in this thread | | | Date | Tue, 22 Mar 2022 17:14:05 -0400 | Subject | Re: [OpenRISC] [PATCH V2 1/5] asm-generic: ticket-lock: New generic ticket-based spinlock | From | Waiman Long <> |
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On 3/22/22 17:06, Stafford Horne wrote: > On Tue, Mar 22, 2022 at 11:54:37AM -0400, Waiman Long wrote: >> On 3/21/22 23:10, Stafford Horne wrote: >>> Hello, >>> >>> There is a problem with this patch on Big Endian machines, see below. >>> >>> On Sat, Mar 19, 2022 at 11:54:53AM +0800, guoren@kernel.org wrote: >>>> From: Peter Zijlstra <peterz@infradead.org> >>>> >>>> This is a simple, fair spinlock. Specifically it doesn't have all the >>>> subtle memory model dependencies that qspinlock has, which makes it more >>>> suitable for simple systems as it is more likely to be correct. >>>> >>>> [Palmer: commit text] >>>> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com> >>>> >>>> -- >>>> >>>> I have specifically not included Peter's SOB on this, as he sent his >>>> original patch >>>> <https://lore.kernel.org/lkml/YHbBBuVFNnI4kjj3@hirez.programming.kicks-ass.net/> >>>> without one. >>>> --- >>>> include/asm-generic/spinlock.h | 11 +++- >>>> include/asm-generic/spinlock_types.h | 15 +++++ >>>> include/asm-generic/ticket-lock-types.h | 11 ++++ >>>> include/asm-generic/ticket-lock.h | 86 +++++++++++++++++++++++++ >>>> 4 files changed, 120 insertions(+), 3 deletions(-) >>>> create mode 100644 include/asm-generic/spinlock_types.h >>>> create mode 100644 include/asm-generic/ticket-lock-types.h >>>> create mode 100644 include/asm-generic/ticket-lock.h >>>> >>>> diff --git a/include/asm-generic/ticket-lock.h b/include/asm-generic/ticket-lock.h >>>> new file mode 100644 >>>> index 000000000000..59373de3e32a >>>> --- /dev/null >>>> +++ b/include/asm-generic/ticket-lock.h >>> ... >>> >>>> +static __always_inline void ticket_unlock(arch_spinlock_t *lock) >>>> +{ >>>> + u16 *ptr = (u16 *)lock + __is_defined(__BIG_ENDIAN); >>> As mentioned, this patch series breaks SMP on OpenRISC. I traced it to this >>> line. The above `__is_defined(__BIG_ENDIAN)` does not return 1 as expected >>> even on BIG_ENDIAN machines. This works: >>> >>> >>> diff --git a/include/asm-generic/ticket-lock.h b/include/asm-generic/ticket-lock.h >>> index 59373de3e32a..52b5dc9ffdba 100644 >>> --- a/include/asm-generic/ticket-lock.h >>> +++ b/include/asm-generic/ticket-lock.h >>> @@ -26,6 +26,7 @@ >>> #define __ASM_GENERIC_TICKET_LOCK_H >>> #include <linux/atomic.h> >>> +#include <linux/kconfig.h> >>> #include <asm-generic/ticket-lock-types.h> >>> static __always_inline void ticket_lock(arch_spinlock_t *lock) >>> @@ -51,7 +52,7 @@ static __always_inline bool ticket_trylock(arch_spinlock_t *lock) >>> static __always_inline void ticket_unlock(arch_spinlock_t *lock) >>> { >>> - u16 *ptr = (u16 *)lock + __is_defined(__BIG_ENDIAN); >>> + u16 *ptr = (u16 *)lock + IS_ENABLED(CONFIG_CPU_BIG_ENDIAN); >>> u32 val = atomic_read(lock); >>> smp_store_release(ptr, (u16)val + 1); >>> >>> >>>> + u32 val = atomic_read(lock); >>>> + >>>> + smp_store_release(ptr, (u16)val + 1); >>>> +} >>>> + >> __BIG_ENDIAN is defined in <linux/kconfig.h>. I believe that if you include >> <linux/kconfig.h>, the second hunk is not really needed and vice versa. > I thought so too, but it doesn't seem to work. I think __is_defined is not > doing what we think in this context. It looks like __is_defined works when a > macro is defined as 1, in this case we have __BIG_ENDIAN 4321.
You are right. __is_defined() only for 1 or not 1. So it can't be used for __BIG_ENDIAN.
I was not aware of that. Anyway, the <linux/kconfig.h> include is not really needed then.
Cheers, Longman
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