LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <longman@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, linux-sh@vger.kernel.org,
	sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org,
	linux-arch@vger.kernel.org, x86@kernel.org,
	Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Tim Chen <tim.c.chen@linux.intel.com>
Subject: Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
Date: Mon, 11 Feb 2019 10:36:01 +0100
Message-ID: <20190211093601.GT32511@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1549850450-10171-1-git-send-email-longman@redhat.com>

On Sun, Feb 10, 2019 at 09:00:50PM -0500, Waiman Long wrote:
> diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h
> index bad2bca..067e265 100644
> --- a/kernel/locking/rwsem.h
> +++ b/kernel/locking/rwsem.h
> @@ -32,6 +32,26 @@
>  # define DEBUG_RWSEMS_WARN_ON(c)
>  #endif
>  
> +/*
> + * R/W semaphores originally for PPC using the stuff in lib/rwsem.c.
> + * Adapted largely from include/asm-i386/rwsem.h
> + * by Paul Mackerras <paulus@samba.org>.
> + */
> +
> +/*
> + * the semaphore definition
> + */
> +#ifdef CONFIG_64BIT
> +# define RWSEM_ACTIVE_MASK		0xffffffffL
> +#else
> +# define RWSEM_ACTIVE_MASK		0x0000ffffL
> +#endif
> +
> +#define RWSEM_ACTIVE_BIAS		0x00000001L
> +#define RWSEM_WAITING_BIAS		(-RWSEM_ACTIVE_MASK-1)
> +#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
> +#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
> +
>  #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
>  /*
>   * All writes to owner are protected by WRITE_ONCE() to make sure that
> @@ -132,3 +152,113 @@ static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
>  {
>  }
>  #endif
> +
> +#ifdef CONFIG_RWSEM_XCHGADD_ALGORITHM
> +/*
> + * lock for reading
> + */
> +static inline void __down_read(struct rw_semaphore *sem)
> +{
> +	if (unlikely(atomic_long_inc_return_acquire(&sem->count) <= 0))
> +		rwsem_down_read_failed(sem);
> +}
> +
> +static inline int __down_read_killable(struct rw_semaphore *sem)
> +{
> +	if (unlikely(atomic_long_inc_return_acquire(&sem->count) <= 0)) {
> +		if (IS_ERR(rwsem_down_read_failed_killable(sem)))
> +			return -EINTR;
> +	}
> +
> +	return 0;
> +}
> +
> +static inline int __down_read_trylock(struct rw_semaphore *sem)
> +{
> +	long tmp;
> +
> +	while ((tmp = atomic_long_read(&sem->count)) >= 0) {
> +		if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
> +				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
> +			return 1;

That really wants to be:

		if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
						    tmp + RWSEM_ACTIVE_READ_BIAS))

> +		}
> +	}
> +	return 0;
> +}
> +
> +/*
> + * lock for writing
> + */
> +static inline void __down_write(struct rw_semaphore *sem)
> +{
> +	long tmp;
> +
> +	tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
> +					     &sem->count);
> +	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
> +		rwsem_down_write_failed(sem);
> +}
> +
> +static inline int __down_write_killable(struct rw_semaphore *sem)
> +{
> +	long tmp;
> +
> +	tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
> +					     &sem->count);
> +	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
> +		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
> +			return -EINTR;
> +	return 0;
> +}
> +
> +static inline int __down_write_trylock(struct rw_semaphore *sem)
> +{
> +	long tmp;

	tmp = RWSEM_UNLOCKED_VALUE;

> +
> +	tmp = atomic_long_cmpxchg_acquire(&sem->count, RWSEM_UNLOCKED_VALUE,
> +		      RWSEM_ACTIVE_WRITE_BIAS);
> +	return tmp == RWSEM_UNLOCKED_VALUE;

	return atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
					       RWSEM_ACTIVE_WRITE_BIAS);

> +}
> +
> +/*
> + * unlock after reading
> + */
> +static inline void __up_read(struct rw_semaphore *sem)
> +{
> +	long tmp;
> +
> +	tmp = atomic_long_dec_return_release(&sem->count);
> +	if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
> +		rwsem_wake(sem);
> +}
> +
> +/*
> + * unlock after writing
> + */
> +static inline void __up_write(struct rw_semaphore *sem)
> +{
> +	if (unlikely(atomic_long_sub_return_release(RWSEM_ACTIVE_WRITE_BIAS,
> +						    &sem->count) < 0))
> +		rwsem_wake(sem);
> +}
> +
> +/*
> + * downgrade write lock to read lock
> + */
> +static inline void __downgrade_write(struct rw_semaphore *sem)
> +{
> +	long tmp;
> +
> +	/*
> +	 * When downgrading from exclusive to shared ownership,
> +	 * anything inside the write-locked region cannot leak
> +	 * into the read side. In contrast, anything in the
> +	 * read-locked region is ok to be re-ordered into the
> +	 * write side. As such, rely on RELEASE semantics.
> +	 */
> +	tmp = atomic_long_add_return_release(-RWSEM_WAITING_BIAS, &sem->count);
> +	if (tmp < 0)
> +		rwsem_downgrade_wake(sem);
> +}
> +
> +#endif /* CONFIG_RWSEM_XCHGADD_ALGORITHM */

  parent reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-11  2:00 Waiman Long
2019-02-11  2:08 ` Waiman Long
2019-02-11  7:11   ` Ingo Molnar
2019-02-11 10:39     ` Ingo Molnar
2019-02-11 10:52       ` Will Deacon
2019-02-11 10:55         ` Ingo Molnar
2019-02-11 13:32       ` Waiman Long
2019-02-11  9:36 ` Peter Zijlstra [this message]
2019-02-11  9:40   ` Peter Zijlstra
2019-02-11 10:57     ` Peter Zijlstra
2019-02-11 11:58 ` Peter Zijlstra
2019-02-11 16:35   ` Waiman Long
2019-02-11 17:04     ` Peter Zijlstra

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190211093601.GT32511@hirez.programming.kicks-ass.net \
    --to=peterz@infradead.org \
    --cc=akpm@linux-foundation.org \
    --cc=arnd@arndb.de \
    --cc=bp@alien8.de \
    --cc=dave@stgolabs.net \
    --cc=hpa@zytor.com \
    --cc=linux-alpha@vger.kernel.org \
    --cc=linux-arch@vger.kernel.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-hexagon@vger.kernel.org \
    --cc=linux-ia64@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-sh@vger.kernel.org \
    --cc=linux-xtensa@linux-xtensa.org \
    --cc=linuxppc-dev@lists.ozlabs.org \
    --cc=longman@redhat.com \
    --cc=mingo@redhat.com \
    --cc=sparclinux@vger.kernel.org \
    --cc=tglx@linutronix.de \
    --cc=tim.c.chen@linux.intel.com \
    --cc=torvalds@linux-foundation.org \
    --cc=will.deacon@arm.com \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org linux-kernel@archiver.kernel.org
	public-inbox-index lkml


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/ public-inbox