Messages in this thread | | | Date | Tue, 22 Mar 2022 11:54:37 -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 3/21/22 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.
Cheers, Longman
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