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16477cdfef
The asm-generic tree contains three separate changes for linux-5.19:
- The h8300 architecture is retired after it has been effectively
unmaintained for a number of years. This is the last architecture we
supported that has no MMU implementation, but there are still a few
architectures (arm, m68k, riscv, sh and xtensa) that support CPUs with
and without an MMU.
- A series to add a generic ticket spinlock that can be shared by most
architectures with a working cmpxchg or ll/sc type atomic, including
the conversion of riscv, csky and openrisc. This series is also a
prerequisite for the loongarch64 architecture port that will come as
a separate pull request.
- A cleanup of some exported uapi header files to ensure they can be
included from user space without relying on other kernel headers.
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Merge tag 'asm-generic-5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic
Pull asm-generic updates from Arnd Bergmann:
"The asm-generic tree contains three separate changes for linux-5.19:
- The h8300 architecture is retired after it has been effectively
unmaintained for a number of years. This is the last architecture
we supported that has no MMU implementation, but there are still a
few architectures (arm, m68k, riscv, sh and xtensa) that support
CPUs with and without an MMU.
- A series to add a generic ticket spinlock that can be shared by
most architectures with a working cmpxchg or ll/sc type atomic,
including the conversion of riscv, csky and openrisc. This series
is also a prerequisite for the loongarch64 architecture port that
will come as a separate pull request.
- A cleanup of some exported uapi header files to ensure they can be
included from user space without relying on other kernel headers"
* tag 'asm-generic-5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic:
h8300: remove stale bindings and symlink
sparc: add asm/stat.h to UAPI compile-test coverage
powerpc: add asm/stat.h to UAPI compile-test coverage
mips: add asm/stat.h to UAPI compile-test coverage
riscv: add linux/bpf_perf_event.h to UAPI compile-test coverage
kbuild: prevent exported headers from including <stdlib.h>, <stdbool.h>
agpgart.h: do not include <stdlib.h> from exported header
csky: Move to generic ticket-spinlock
RISC-V: Move to queued RW locks
RISC-V: Move to generic spinlocks
openrisc: Move to ticket-spinlock
asm-generic: qrwlock: Document the spinlock fairness requirements
asm-generic: qspinlock: Indicate the use of mixed-size atomics
asm-generic: ticket-lock: New generic ticket-based spinlock
remove the h8300 architecture
147 lines
4 KiB
C
147 lines
4 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/*
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* Queue read/write lock
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*
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* These use generic atomic and locking routines, but depend on a fair spinlock
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* implementation in order to be fair themselves. The implementation in
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* asm-generic/spinlock.h meets these requirements.
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*
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* (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
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*
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* Authors: Waiman Long <waiman.long@hp.com>
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*/
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#ifndef __ASM_GENERIC_QRWLOCK_H
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#define __ASM_GENERIC_QRWLOCK_H
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#include <linux/atomic.h>
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#include <asm/barrier.h>
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#include <asm/processor.h>
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#include <asm-generic/qrwlock_types.h>
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/* Must be included from asm/spinlock.h after defining arch_spin_is_locked. */
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/*
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* Writer states & reader shift and bias.
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*/
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#define _QW_WAITING 0x100 /* A writer is waiting */
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#define _QW_LOCKED 0x0ff /* A writer holds the lock */
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#define _QW_WMASK 0x1ff /* Writer mask */
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#define _QR_SHIFT 9 /* Reader count shift */
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#define _QR_BIAS (1U << _QR_SHIFT)
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/*
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* External function declarations
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*/
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extern void queued_read_lock_slowpath(struct qrwlock *lock);
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extern void queued_write_lock_slowpath(struct qrwlock *lock);
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/**
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* queued_read_trylock - try to acquire read lock of a queued rwlock
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* @lock : Pointer to queued rwlock structure
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* Return: 1 if lock acquired, 0 if failed
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*/
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static inline int queued_read_trylock(struct qrwlock *lock)
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{
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int cnts;
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cnts = atomic_read(&lock->cnts);
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if (likely(!(cnts & _QW_WMASK))) {
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cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
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if (likely(!(cnts & _QW_WMASK)))
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return 1;
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atomic_sub(_QR_BIAS, &lock->cnts);
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}
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return 0;
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}
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/**
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* queued_write_trylock - try to acquire write lock of a queued rwlock
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* @lock : Pointer to queued rwlock structure
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* Return: 1 if lock acquired, 0 if failed
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*/
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static inline int queued_write_trylock(struct qrwlock *lock)
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{
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int cnts;
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cnts = atomic_read(&lock->cnts);
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if (unlikely(cnts))
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return 0;
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return likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts,
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_QW_LOCKED));
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}
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/**
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* queued_read_lock - acquire read lock of a queued rwlock
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* @lock: Pointer to queued rwlock structure
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*/
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static inline void queued_read_lock(struct qrwlock *lock)
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{
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int cnts;
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cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
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if (likely(!(cnts & _QW_WMASK)))
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return;
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/* The slowpath will decrement the reader count, if necessary. */
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queued_read_lock_slowpath(lock);
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}
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/**
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* queued_write_lock - acquire write lock of a queued rwlock
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* @lock : Pointer to queued rwlock structure
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*/
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static inline void queued_write_lock(struct qrwlock *lock)
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{
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int cnts = 0;
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/* Optimize for the unfair lock case where the fair flag is 0. */
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if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED)))
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return;
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queued_write_lock_slowpath(lock);
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}
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/**
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* queued_read_unlock - release read lock of a queued rwlock
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* @lock : Pointer to queued rwlock structure
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*/
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static inline void queued_read_unlock(struct qrwlock *lock)
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{
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/*
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* Atomically decrement the reader count
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*/
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(void)atomic_sub_return_release(_QR_BIAS, &lock->cnts);
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}
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/**
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* queued_write_unlock - release write lock of a queued rwlock
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* @lock : Pointer to queued rwlock structure
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*/
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static inline void queued_write_unlock(struct qrwlock *lock)
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{
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smp_store_release(&lock->wlocked, 0);
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}
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/**
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* queued_rwlock_is_contended - check if the lock is contended
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* @lock : Pointer to queued rwlock structure
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* Return: 1 if lock contended, 0 otherwise
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*/
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static inline int queued_rwlock_is_contended(struct qrwlock *lock)
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{
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return arch_spin_is_locked(&lock->wait_lock);
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}
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/*
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* Remapping rwlock architecture specific functions to the corresponding
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* queued rwlock functions.
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*/
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#define arch_read_lock(l) queued_read_lock(l)
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#define arch_write_lock(l) queued_write_lock(l)
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#define arch_read_trylock(l) queued_read_trylock(l)
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#define arch_write_trylock(l) queued_write_trylock(l)
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#define arch_read_unlock(l) queued_read_unlock(l)
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#define arch_write_unlock(l) queued_write_unlock(l)
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#define arch_rwlock_is_contended(l) queued_rwlock_is_contended(l)
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#endif /* __ASM_GENERIC_QRWLOCK_H */
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