From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <longman@redhat.com>
Cc: linux-arch@vger.kernel.org, linux-xtensa@linux-xtensa.org,
Davidlohr Bueso <dave@stgolabs.net>,
linux-ia64@vger.kernel.org, Tim Chen <tim.c.chen@linux.intel.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-sh@vger.kernel.org, linux-hexagon@vger.kernel.org,
x86@kernel.org, Will Deacon <will.deacon@arm.com>,
linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
linux-alpha@vger.kernel.org, sparclinux@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
linuxppc-dev@lists.ozlabs.org,
Andrew Morton <akpm@linux-foundation.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
Date: Mon, 11 Feb 2019 10:36:01 +0100 [thread overview]
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 */
next prev parent reply other threads:[~2019-02-11 9:38 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-11 2:00 [PATCH] locking/rwsem: Remove arch specific rwsem files 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
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