linux-kernel - Re: [PATCH 10/11] x86, rwsem: provide __down_write

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Date:	Wed, 13 Apr 2016 11:08:30 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"David S. Miller" <davem@...emloft.net>,
	Tony Luck <tony.luck@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Zankel <chris@...kel.net>,
	Max Filippov <jcmvbkbc@...il.com>, x86@...nel.org,
	linux-alpha@...r.kernel.org, linux-ia64@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
	sparclinux@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
	linux-arch@...r.kernel.org, Michal Hocko <mhocko@...e.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable


* Michal Hocko <mhocko@...nel.org> wrote:

> From: Michal Hocko <mhocko@...e.com>
> 
> which uses the same fast path as __down_write except it falls back to
> call_rwsem_down_write_failed_killable slow path and return -EINTR if
> killed. To prevent from code duplication extract the skeleton of
> __down_write into a helper macro which just takes the semaphore
> and the slow path function to be called.
> 
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> ---
>  arch/x86/include/asm/rwsem.h | 41 ++++++++++++++++++++++++++++-------------
>  arch/x86/lib/rwsem.S         |  8 ++++++++
>  2 files changed, 36 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h
> index d79a218675bc..4c3d90dbe89a 100644
> --- a/arch/x86/include/asm/rwsem.h
> +++ b/arch/x86/include/asm/rwsem.h
> @@ -99,21 +99,36 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
>  /*
>   * lock for writing
>   */
> +#define ____down_write(sem, slow_path)			\
> +({							\
> +	long tmp;					\
> +	struct rw_semaphore* ret = sem;			\
> +	asm volatile("# beginning down_write\n\t"	\
> +		     LOCK_PREFIX "  xadd      %1,(%2)\n\t"	\
> +		     /* adds 0xffff0001, returns the old value */ \
> +		     "  test " __ASM_SEL(%w1,%k1) "," __ASM_SEL(%w1,%k1) "\n\t" \
> +		     /* was the active mask 0 before? */\
> +		     "  jz        1f\n"			\
> +		     "  call " slow_path "\n"		\
> +		     "1:\n"				\
> +		     "# ending down_write"		\
> +		     : "+m" (sem->count), "=d" (tmp), "+a" (ret)	\
> +		     : "a" (sem), "1" (RWSEM_ACTIVE_WRITE_BIAS) \
> +		     : "memory", "cc");			\
> +	ret;						\
> +})
> +
>  static inline void __down_write(struct rw_semaphore *sem)
>  {
> -	long tmp;
> -	asm volatile("# beginning down_write\n\t"
> -		     LOCK_PREFIX "  xadd      %1,(%2)\n\t"
> -		     /* adds 0xffff0001, returns the old value */
> -		     "  test " __ASM_SEL(%w1,%k1) "," __ASM_SEL(%w1,%k1) "\n\t"
> -		     /* was the active mask 0 before? */
> -		     "  jz        1f\n"
> -		     "  call call_rwsem_down_write_failed\n"
> -		     "1:\n"
> -		     "# ending down_write"
> -		     : "+m" (sem->count), "=d" (tmp)
> -		     : "a" (sem), "1" (RWSEM_ACTIVE_WRITE_BIAS)
> -		     : "memory", "cc");
> +	____down_write(sem, "call_rwsem_down_write_failed");
> +}
> +
> +static inline int __down_write_killable(struct rw_semaphore *sem)
> +{
> +	if (IS_ERR(____down_write(sem, "call_rwsem_down_write_failed_killable")))
> +		return -EINTR;
> +
> +	return 0;
>  }
>  
>  /*
> diff --git a/arch/x86/lib/rwsem.S b/arch/x86/lib/rwsem.S
> index 40027db99140..d1a1397e1fb3 100644
> --- a/arch/x86/lib/rwsem.S
> +++ b/arch/x86/lib/rwsem.S
> @@ -101,6 +101,14 @@ ENTRY(call_rwsem_down_write_failed)
>  	ret
>  ENDPROC(call_rwsem_down_write_failed)
>  
> +ENTRY(call_rwsem_down_write_failed_killable)
> +	save_common_regs
> +	movq %rax,%rdi
> +	call rwsem_down_write_failed_killable
> +	restore_common_regs
> +	ret
> +ENDPROC(call_rwsem_down_write_failed_killable)

Got this objtool warning on x86-64 allyesconfig:

  arch/x86/lib/rwsem.o: warning: objtool: call_rwsem_down_write_failed_killable()+0xe: call without frame pointer save/setup

Thanks,

	Ingo