Re: [PATCH v2 06/28] locking/rwlocks: Add contention detection for rwlocks

[Guenter Roeck]

On Tue, Feb 09, 2021 at 04:46:02PM -0500, Waiman Long wrote:
> On 2/9/21 3:39 PM, Guenter Roeck wrote:
> > On Tue, Feb 02, 2021 at 10:57:12AM -0800, Ben Gardon wrote:
> > > rwlocks do not currently have any facility to detect contention
> > > like spinlocks do. In order to allow users of rwlocks to better manage
> > > latency, add contention detection for queued rwlocks.
> > > 
> > > CC: Ingo Molnar <mingo@xxxxxxxxxx>
> > > CC: Will Deacon <will@xxxxxxxxxx>
> > > Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > > Acked-by: Davidlohr Bueso <dbueso@xxxxxxx>
> > > Acked-by: Waiman Long <longman@xxxxxxxxxx>
> > > Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > > Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>
> > When building mips:defconfig, this patch results in:
> > 
> > Error log:
> > In file included from include/linux/spinlock.h:90,
> >                   from include/linux/ipc.h:5,
> >                   from include/uapi/linux/sem.h:5,
> >                   from include/linux/sem.h:5,
> >                   from include/linux/compat.h:14,
> >                   from arch/mips/kernel/asm-offsets.c:12:
> > arch/mips/include/asm/spinlock.h:17:28: error: redefinition of 'queued_spin_unlock'
> >     17 | #define queued_spin_unlock queued_spin_unlock
> >        |                            ^~~~~~~~~~~~~~~~~~
> > arch/mips/include/asm/spinlock.h:22:20: note: in expansion of macro 'queued_spin_unlock'
> >     22 | static inline void queued_spin_unlock(struct qspinlock *lock)
> >        |                    ^~~~~~~~~~~~~~~~~~
> > In file included from include/asm-generic/qrwlock.h:17,
> >                   from ./arch/mips/include/generated/asm/qrwlock.h:1,
> >                   from arch/mips/include/asm/spinlock.h:13,
> >                   from include/linux/spinlock.h:90,
> >                   from include/linux/ipc.h:5,
> >                   from include/uapi/linux/sem.h:5,
> >                   from include/linux/sem.h:5,
> >                   from include/linux/compat.h:14,
> >                   from arch/mips/kernel/asm-offsets.c:12:
> > include/asm-generic/qspinlock.h:94:29: note: previous definition of 'queued_spin_unlock' was here
> >     94 | static __always_inline void queued_spin_unlock(struct qspinlock *lock)
> >        |                             ^~~~~~~~~~~~~~~~~~
> 
> I think the compile error is caused by the improper header file inclusion
> ordering. Can you try the following change to see if it can fix the compile
> error?
> 

That results in:

In file included from ./arch/mips/include/generated/asm/qrwlock.h:1,
                 from ./arch/mips/include/asm/spinlock.h:13,
                 from ./include/linux/spinlock.h:90,
                 from ./include/linux/ipc.h:5,
                 from ./include/uapi/linux/sem.h:5,
                 from ./include/linux/sem.h:5,
                 from ./include/linux/compat.h:14,
                 from arch/mips/kernel/asm-offsets.c:12:
./include/asm-generic/qrwlock.h: In function 'queued_rwlock_is_contended':
./include/asm-generic/qrwlock.h:127:9: error: implicit declaration of function 'arch_spin_is_locked'

Guenter

> Cheers,
> Longman
> 
> diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
> index 0020d3b820a7..d7178a9439b5 100644
> --- a/include/asm-generic/qrwlock.h
> +++ b/include/asm-generic/qrwlock.h
> @@ -10,11 +10,11 @@
>  #define __ASM_GENERIC_QRWLOCK_H
> 
>  #include <linux/atomic.h>
> +#include <linux/spinlock.h>
>  #include <asm/barrier.h>
>  #include <asm/processor.h>
> 
>  #include <asm-generic/qrwlock_types.h>
> -#include <asm-generic/qspinlock.h>
> 
>  /*
>   * Writer states & reader shift and bias.
> 
> 
>