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

[Waiman Long]

On 2/9/21 5:25 PM, Guenter Roeck wrote:
> 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

It is because in arch/mips/include/asm/spinlock.h, asm/qrwlock.h is 
included before asm/qspinlock.h. The compilation error should be gone if 
the asm/qrwlock.h is removed or moved after asm/qspinlock.h.

I did a x86 build and there was no compilation issue.

Cheers,
Longman