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Date:   Fri, 22 Oct 2021 16:10:35 +0200
From:   Helge Deller <deller@....de>
To:     Arnd Bergmann <arnd@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
        openrisc@...ts.librecores.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH] locking: remove spin_lock_flags() etc

On 10/22/21 13:59, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
>
> parisc, ia64 and powerpc32 are the only remaining architectures that
> provide custom arch_{spin,read,write}_lock_flags() functions, which are
> meant to re-enable interrupts while waiting for a spinlock.
>
> However, none of these can actually run into this codepath, because
> it is only called on architectures without CONFIG_GENERIC_LOCKBREAK,
> or when CONFIG_DEBUG_LOCK_ALLOC is set without CONFIG_LOCKDEP, and none
> of those combinations are possible on the three architectures.
>
> Going back in the git history, it appears that arch/mn10300 may have
> been able to run into this code path, but there is a good chance that
> it never worked. On the architectures that still exist, it was
> already impossible to hit back in 2008 after the introduction of
> CONFIG_GENERIC_LOCKBREAK, and possibly earlier.
>
> As this is all dead code, just remove it and the helper functions built
> around it. For arch/ia64, the inline asm could be cleaned up, but
> it seems safer to leave it untouched.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Acked-by: Helge Deller <deller@....de>  # parisc

Helge

> ---
>  arch/ia64/include/asm/spinlock.h           | 23 ++++++----------------
>  arch/openrisc/include/asm/spinlock.h       |  3 ---
>  arch/parisc/include/asm/spinlock.h         | 15 --------------
>  arch/powerpc/include/asm/simple_spinlock.h | 21 --------------------
>  arch/s390/include/asm/spinlock.h           |  8 --------
>  include/linux/lockdep.h                    | 17 ----------------
>  include/linux/rwlock.h                     | 15 --------------
>  include/linux/rwlock_api_smp.h             |  6 ++----
>  include/linux/spinlock.h                   | 13 ------------
>  include/linux/spinlock_api_smp.h           |  9 ---------
>  include/linux/spinlock_up.h                |  1 -
>  kernel/locking/spinlock.c                  |  3 +--
>  12 files changed, 9 insertions(+), 125 deletions(-)
>
> diff --git a/arch/ia64/include/asm/spinlock.h b/arch/ia64/include/asm/spinlock.h
> index 864775970c50..0e5c1ad3239c 100644
> --- a/arch/ia64/include/asm/spinlock.h
> +++ b/arch/ia64/include/asm/spinlock.h
> @@ -124,18 +124,13 @@ static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
>  	__ticket_spin_unlock(lock);
>  }
>
> -static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
> -						  unsigned long flags)
> -{
> -	arch_spin_lock(lock);
> -}
> -#define arch_spin_lock_flags	arch_spin_lock_flags
> -
>  #ifdef ASM_SUPPORTED
>
>  static __always_inline void
> -arch_read_lock_flags(arch_rwlock_t *lock, unsigned long flags)
> +arch_read_lock(arch_rwlock_t *lock)
>  {
> +	unsigned long flags = 0;
> +
>  	__asm__ __volatile__ (
>  		"tbit.nz p6, p0 = %1,%2\n"
>  		"br.few 3f\n"
> @@ -157,13 +152,8 @@ arch_read_lock_flags(arch_rwlock_t *lock, unsigned long flags)
>  		: "p6", "p7", "r2", "memory");
>  }
>
> -#define arch_read_lock_flags arch_read_lock_flags
> -#define arch_read_lock(lock) arch_read_lock_flags(lock, 0)
> -
>  #else /* !ASM_SUPPORTED */
>
> -#define arch_read_lock_flags(rw, flags) arch_read_lock(rw)
> -
>  #define arch_read_lock(rw)								\
>  do {											\
>  	arch_rwlock_t *__read_lock_ptr = (rw);						\
> @@ -186,8 +176,10 @@ do {								\
>  #ifdef ASM_SUPPORTED
>
>  static __always_inline void
> -arch_write_lock_flags(arch_rwlock_t *lock, unsigned long flags)
> +arch_write_lock(arch_rwlock_t *lock)
>  {
> +	unsigned long flags = 0;
> +
>  	__asm__ __volatile__ (
>  		"tbit.nz p6, p0 = %1, %2\n"
>  		"mov ar.ccv = r0\n"
> @@ -210,9 +202,6 @@ arch_write_lock_flags(arch_rwlock_t *lock, unsigned long flags)
>  		: "ar.ccv", "p6", "p7", "r2", "r29", "memory");
>  }
>
> -#define arch_write_lock_flags arch_write_lock_flags
> -#define arch_write_lock(rw) arch_write_lock_flags(rw, 0)
> -
>  #define arch_write_trylock(rw)							\
>  ({										\
>  	register long result;							\
> diff --git a/arch/openrisc/include/asm/spinlock.h b/arch/openrisc/include/asm/spinlock.h
> index a8940bdfcb7e..264944a71535 100644
> --- a/arch/openrisc/include/asm/spinlock.h
> +++ b/arch/openrisc/include/asm/spinlock.h
> @@ -19,9 +19,6 @@
>
>  #include <asm/qrwlock.h>
>
> -#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
> -#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
> -
>  #define arch_spin_relax(lock)	cpu_relax()
>  #define arch_read_relax(lock)	cpu_relax()
>  #define arch_write_relax(lock)	cpu_relax()
> diff --git a/arch/parisc/include/asm/spinlock.h b/arch/parisc/include/asm/spinlock.h
> index fa5ee8a45dbd..a6e5d66a7656 100644
> --- a/arch/parisc/include/asm/spinlock.h
> +++ b/arch/parisc/include/asm/spinlock.h
> @@ -23,21 +23,6 @@ static inline void arch_spin_lock(arch_spinlock_t *x)
>  			continue;
>  }
>
> -static inline void arch_spin_lock_flags(arch_spinlock_t *x,
> -					unsigned long flags)
> -{
> -	volatile unsigned int *a;
> -
> -	a = __ldcw_align(x);
> -	while (__ldcw(a) == 0)
> -		while (*a == 0)
> -			if (flags & PSW_SM_I) {
> -				local_irq_enable();
> -				local_irq_disable();
> -			}
> -}
> -#define arch_spin_lock_flags arch_spin_lock_flags
> -
>  static inline void arch_spin_unlock(arch_spinlock_t *x)
>  {
>  	volatile unsigned int *a;
> diff --git a/arch/powerpc/include/asm/simple_spinlock.h b/arch/powerpc/include/asm/simple_spinlock.h
> index 8985791a2ba5..7ae6aeef8464 100644
> --- a/arch/powerpc/include/asm/simple_spinlock.h
> +++ b/arch/powerpc/include/asm/simple_spinlock.h
> @@ -123,27 +123,6 @@ static inline void arch_spin_lock(arch_spinlock_t *lock)
>  	}
>  }
>
> -static inline
> -void arch_spin_lock_flags(arch_spinlock_t *lock, unsigned long flags)
> -{
> -	unsigned long flags_dis;
> -
> -	while (1) {
> -		if (likely(__arch_spin_trylock(lock) == 0))
> -			break;
> -		local_save_flags(flags_dis);
> -		local_irq_restore(flags);
> -		do {
> -			HMT_low();
> -			if (is_shared_processor())
> -				splpar_spin_yield(lock);
> -		} while (unlikely(lock->slock != 0));
> -		HMT_medium();
> -		local_irq_restore(flags_dis);
> -	}
> -}
> -#define arch_spin_lock_flags arch_spin_lock_flags
> -
>  static inline void arch_spin_unlock(arch_spinlock_t *lock)
>  {
>  	__asm__ __volatile__("# arch_spin_unlock\n\t"
> diff --git a/arch/s390/include/asm/spinlock.h b/arch/s390/include/asm/spinlock.h
> index ef59588a3042..888a2f1c9ee3 100644
> --- a/arch/s390/include/asm/spinlock.h
> +++ b/arch/s390/include/asm/spinlock.h
> @@ -67,14 +67,6 @@ static inline void arch_spin_lock(arch_spinlock_t *lp)
>  		arch_spin_lock_wait(lp);
>  }
>
> -static inline void arch_spin_lock_flags(arch_spinlock_t *lp,
> -					unsigned long flags)
> -{
> -	if (!arch_spin_trylock_once(lp))
> -		arch_spin_lock_wait(lp);
> -}
> -#define arch_spin_lock_flags	arch_spin_lock_flags
> -
>  static inline int arch_spin_trylock(arch_spinlock_t *lp)
>  {
>  	if (!arch_spin_trylock_once(lp))
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index 9fe165beb0f9..467b94257105 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -481,23 +481,6 @@ do {								\
>
>  #endif /* CONFIG_LOCK_STAT */
>
> -#ifdef CONFIG_LOCKDEP
> -
> -/*
> - * On lockdep we dont want the hand-coded irq-enable of
> - * _raw_*_lock_flags() code, because lockdep assumes
> - * that interrupts are not re-enabled during lock-acquire:
> - */
> -#define LOCK_CONTENDED_FLAGS(_lock, try, lock, lockfl, flags) \
> -	LOCK_CONTENDED((_lock), (try), (lock))
> -
> -#else /* CONFIG_LOCKDEP */
> -
> -#define LOCK_CONTENDED_FLAGS(_lock, try, lock, lockfl, flags) \
> -	lockfl((_lock), (flags))
> -
> -#endif /* CONFIG_LOCKDEP */
> -
>  #ifdef CONFIG_PROVE_LOCKING
>  extern void print_irqtrace_events(struct task_struct *curr);
>  #else
> diff --git a/include/linux/rwlock.h b/include/linux/rwlock.h
> index 7ce9a51ae5c0..2c0ad417ce3c 100644
> --- a/include/linux/rwlock.h
> +++ b/include/linux/rwlock.h
> @@ -30,31 +30,16 @@ do {								\
>
>  #ifdef CONFIG_DEBUG_SPINLOCK
>   extern void do_raw_read_lock(rwlock_t *lock) __acquires(lock);
> -#define do_raw_read_lock_flags(lock, flags) do_raw_read_lock(lock)
>   extern int do_raw_read_trylock(rwlock_t *lock);
>   extern void do_raw_read_unlock(rwlock_t *lock) __releases(lock);
>   extern void do_raw_write_lock(rwlock_t *lock) __acquires(lock);
> -#define do_raw_write_lock_flags(lock, flags) do_raw_write_lock(lock)
>   extern int do_raw_write_trylock(rwlock_t *lock);
>   extern void do_raw_write_unlock(rwlock_t *lock) __releases(lock);
>  #else
> -
> -#ifndef arch_read_lock_flags
> -# define arch_read_lock_flags(lock, flags)	arch_read_lock(lock)
> -#endif
> -
> -#ifndef arch_write_lock_flags
> -# define arch_write_lock_flags(lock, flags)	arch_write_lock(lock)
> -#endif
> -
>  # define do_raw_read_lock(rwlock)	do {__acquire(lock); arch_read_lock(&(rwlock)->raw_lock); } while (0)
> -# define do_raw_read_lock_flags(lock, flags) \
> -		do {__acquire(lock); arch_read_lock_flags(&(lock)->raw_lock, *(flags)); } while (0)
>  # define do_raw_read_trylock(rwlock)	arch_read_trylock(&(rwlock)->raw_lock)
>  # define do_raw_read_unlock(rwlock)	do {arch_read_unlock(&(rwlock)->raw_lock); __release(lock); } while (0)
>  # define do_raw_write_lock(rwlock)	do {__acquire(lock); arch_write_lock(&(rwlock)->raw_lock); } while (0)
> -# define do_raw_write_lock_flags(lock, flags) \
> -		do {__acquire(lock); arch_write_lock_flags(&(lock)->raw_lock, *(flags)); } while (0)
>  # define do_raw_write_trylock(rwlock)	arch_write_trylock(&(rwlock)->raw_lock)
>  # define do_raw_write_unlock(rwlock)	do {arch_write_unlock(&(rwlock)->raw_lock); __release(lock); } while (0)
>  #endif
> diff --git a/include/linux/rwlock_api_smp.h b/include/linux/rwlock_api_smp.h
> index abfb53ab11be..f1db6f17c4fb 100644
> --- a/include/linux/rwlock_api_smp.h
> +++ b/include/linux/rwlock_api_smp.h
> @@ -157,8 +157,7 @@ static inline unsigned long __raw_read_lock_irqsave(rwlock_t *lock)
>  	local_irq_save(flags);
>  	preempt_disable();
>  	rwlock_acquire_read(&lock->dep_map, 0, 0, _RET_IP_);
> -	LOCK_CONTENDED_FLAGS(lock, do_raw_read_trylock, do_raw_read_lock,
> -			     do_raw_read_lock_flags, &flags);
> +	LOCK_CONTENDED(lock, do_raw_read_trylock, do_raw_read_lock);
>  	return flags;
>  }
>
> @@ -184,8 +183,7 @@ static inline unsigned long __raw_write_lock_irqsave(rwlock_t *lock)
>  	local_irq_save(flags);
>  	preempt_disable();
>  	rwlock_acquire(&lock->dep_map, 0, 0, _RET_IP_);
> -	LOCK_CONTENDED_FLAGS(lock, do_raw_write_trylock, do_raw_write_lock,
> -			     do_raw_write_lock_flags, &flags);
> +	LOCK_CONTENDED(lock, do_raw_write_trylock, do_raw_write_lock);
>  	return flags;
>  }
>
> diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
> index c04e99edfe92..40e467cdee2d 100644
> --- a/include/linux/spinlock.h
> +++ b/include/linux/spinlock.h
> @@ -176,7 +176,6 @@ do {									\
>
>  #ifdef CONFIG_DEBUG_SPINLOCK
>   extern void do_raw_spin_lock(raw_spinlock_t *lock) __acquires(lock);
> -#define do_raw_spin_lock_flags(lock, flags) do_raw_spin_lock(lock)
>   extern int do_raw_spin_trylock(raw_spinlock_t *lock);
>   extern void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock);
>  #else
> @@ -187,18 +186,6 @@ static inline void do_raw_spin_lock(raw_spinlock_t *lock) __acquires(lock)
>  	mmiowb_spin_lock();
>  }
>
> -#ifndef arch_spin_lock_flags
> -#define arch_spin_lock_flags(lock, flags)	arch_spin_lock(lock)
> -#endif
> -
> -static inline void
> -do_raw_spin_lock_flags(raw_spinlock_t *lock, unsigned long *flags) __acquires(lock)
> -{
> -	__acquire(lock);
> -	arch_spin_lock_flags(&lock->raw_lock, *flags);
> -	mmiowb_spin_lock();
> -}
> -
>  static inline int do_raw_spin_trylock(raw_spinlock_t *lock)
>  {
>  	int ret = arch_spin_trylock(&(lock)->raw_lock);
> diff --git a/include/linux/spinlock_api_smp.h b/include/linux/spinlock_api_smp.h
> index 6b8e1a0b137b..51fa0dab68c4 100644
> --- a/include/linux/spinlock_api_smp.h
> +++ b/include/linux/spinlock_api_smp.h
> @@ -108,16 +108,7 @@ static inline unsigned long __raw_spin_lock_irqsave(raw_spinlock_t *lock)
>  	local_irq_save(flags);
>  	preempt_disable();
>  	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
> -	/*
> -	 * On lockdep we dont want the hand-coded irq-enable of
> -	 * do_raw_spin_lock_flags() code, because lockdep assumes
> -	 * that interrupts are not re-enabled during lock-acquire:
> -	 */
> -#ifdef CONFIG_LOCKDEP
>  	LOCK_CONTENDED(lock, do_raw_spin_trylock, do_raw_spin_lock);
> -#else
> -	do_raw_spin_lock_flags(lock, &flags);
> -#endif
>  	return flags;
>  }
>
> diff --git a/include/linux/spinlock_up.h b/include/linux/spinlock_up.h
> index 0ac9112c1bbe..16521074b6f7 100644
> --- a/include/linux/spinlock_up.h
> +++ b/include/linux/spinlock_up.h
> @@ -62,7 +62,6 @@ static inline void arch_spin_unlock(arch_spinlock_t *lock)
>  #define arch_spin_is_locked(lock)	((void)(lock), 0)
>  /* for sched/core.c and kernel_lock.c: */
>  # define arch_spin_lock(lock)		do { barrier(); (void)(lock); } while (0)
> -# define arch_spin_lock_flags(lock, flags)	do { barrier(); (void)(lock); } while (0)
>  # define arch_spin_unlock(lock)	do { barrier(); (void)(lock); } while (0)
>  # define arch_spin_trylock(lock)	({ barrier(); (void)(lock); 1; })
>  #endif /* DEBUG_SPINLOCK */
> diff --git a/kernel/locking/spinlock.c b/kernel/locking/spinlock.c
> index c5830cfa379a..b562f9289372 100644
> --- a/kernel/locking/spinlock.c
> +++ b/kernel/locking/spinlock.c
> @@ -378,8 +378,7 @@ unsigned long __lockfunc _raw_spin_lock_irqsave_nested(raw_spinlock_t *lock,
>  	local_irq_save(flags);
>  	preempt_disable();
>  	spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
> -	LOCK_CONTENDED_FLAGS(lock, do_raw_spin_trylock, do_raw_spin_lock,
> -				do_raw_spin_lock_flags, &flags);
> +	LOCK_CONTENDED(lock, do_raw_spin_trylock, do_raw_spin_lock);
>  	return flags;
>  }
>  EXPORT_SYMBOL(_raw_spin_lock_irqsave_nested);
>

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