cregit-Linux how code gets into the kernel

Release 4.12 include/asm-generic/qrwlock.h

/*
 * Queue read/write lock
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
 *
 * Authors: Waiman Long <waiman.long@hp.com>
 */
#ifndef __ASM_GENERIC_QRWLOCK_H

#define __ASM_GENERIC_QRWLOCK_H

#include <linux/atomic.h>
#include <asm/barrier.h>
#include <asm/processor.h>

#include <asm-generic/qrwlock_types.h>

/*
 * Writer states & reader shift and bias.
 *
 *       | +0 | +1 | +2 | +3 |
 *   ----+----+----+----+----+
 *    LE | 78 | 56 | 34 | 12 | 0x12345678
 *   ----+----+----+----+----+
 *       | wr |      rd      |
 *       +----+----+----+----+
 *
 *   ----+----+----+----+----+
 *    BE | 12 | 34 | 56 | 78 | 0x12345678
 *   ----+----+----+----+----+
 *       |      rd      | wr |
 *       +----+----+----+----+
 */

#define	_QW_WAITING	1		
/* A writer is waiting     */

#define	_QW_LOCKED	0xff		
/* A writer holds the lock */

#define	_QW_WMASK	0xff		
/* Writer mask             */

#define	_QR_SHIFT	8		
/* Reader count shift      */

#define _QR_BIAS	(1U << _QR_SHIFT)

/*
 * External function declarations
 */
extern void queued_read_lock_slowpath(struct qrwlock *lock, u32 cnts);
extern void queued_write_lock_slowpath(struct qrwlock *lock);

/**
 * queued_read_can_lock- would read_trylock() succeed?
 * @lock: Pointer to queue rwlock structure
 */

static inline int queued_read_can_lock(struct qrwlock *lock) { return !(atomic_read(&lock->cnts) & _QW_WMASK); }

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Waiman Long26100.00%2100.00%
Total26100.00%2100.00%

/** * queued_write_can_lock- would write_trylock() succeed? * @lock: Pointer to queue rwlock structure */
static inline int queued_write_can_lock(struct qrwlock *lock) { return !atomic_read(&lock->cnts); }

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Waiman Long22100.00%2100.00%
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/** * queued_read_trylock - try to acquire read lock of a queue rwlock * @lock : Pointer to queue rwlock structure * Return: 1 if lock acquired, 0 if failed */
static inline int queued_read_trylock(struct qrwlock *lock) { u32 cnts; cnts = atomic_read(&lock->cnts); if (likely(!(cnts & _QW_WMASK))) { cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts); if (likely(!(cnts & _QW_WMASK))) return 1; atomic_sub(_QR_BIAS, &lock->cnts); } return 0; }

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Waiman Long8198.78%266.67%
Will Deacon11.22%133.33%
Total82100.00%3100.00%

/** * queued_write_trylock - try to acquire write lock of a queue rwlock * @lock : Pointer to queue rwlock structure * Return: 1 if lock acquired, 0 if failed */
static inline int queued_write_trylock(struct qrwlock *lock) { u32 cnts; cnts = atomic_read(&lock->cnts); if (unlikely(cnts)) return 0; return likely(atomic_cmpxchg_acquire(&lock->cnts, cnts, cnts | _QW_LOCKED) == cnts); }

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Waiman Long5498.18%266.67%
Will Deacon11.82%133.33%
Total55100.00%3100.00%

/** * queued_read_lock - acquire read lock of a queue rwlock * @lock: Pointer to queue rwlock structure */
static inline void queued_read_lock(struct qrwlock *lock) { u32 cnts; cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts); if (likely(!(cnts & _QW_WMASK))) return; /* The slowpath will decrement the reader count, if necessary. */ queued_read_lock_slowpath(lock, cnts); }

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Waiman Long4797.92%375.00%
Will Deacon12.08%125.00%
Total48100.00%4100.00%

/** * queued_write_lock - acquire write lock of a queue rwlock * @lock : Pointer to queue rwlock structure */
static inline void queued_write_lock(struct qrwlock *lock) { /* Optimize for the unfair lock case where the fair flag is 0. */ if (atomic_cmpxchg_acquire(&lock->cnts, 0, _QW_LOCKED) == 0) return; queued_write_lock_slowpath(lock); }

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Waiman Long3497.14%266.67%
Will Deacon12.86%133.33%
Total35100.00%3100.00%

/** * queued_read_unlock - release read lock of a queue rwlock * @lock : Pointer to queue rwlock structure */
static inline void queued_read_unlock(struct qrwlock *lock) { /* * Atomically decrement the reader count */ (void)atomic_sub_return_release(_QR_BIAS, &lock->cnts); }

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Waiman Long2284.62%266.67%
Will Deacon415.38%133.33%
Total26100.00%3100.00%

/** * __qrwlock_write_byte - retrieve the write byte address of a queue rwlock * @lock : Pointer to queue rwlock structure * Return: the write byte address of a queue rwlock */
static inline u8 *__qrwlock_write_byte(struct qrwlock *lock) { return (u8 *)lock + 3 * IS_BUILTIN(CONFIG_CPU_BIG_ENDIAN); }

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Pan Xinhui27100.00%1100.00%
Total27100.00%1100.00%

/** * queued_write_unlock - release write lock of a queue rwlock * @lock : Pointer to queue rwlock structure */
static inline void queued_write_unlock(struct qrwlock *lock) { smp_store_release(__qrwlock_write_byte(lock), 0); }

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Waiman Long1672.73%250.00%
Will Deacon313.64%125.00%
Pan Xinhui313.64%125.00%
Total22100.00%4100.00%

/* * Remapping rwlock architecture specific functions to the corresponding * queue rwlock functions. */ #define arch_read_can_lock(l) queued_read_can_lock(l) #define arch_write_can_lock(l) queued_write_can_lock(l) #define arch_read_lock(l) queued_read_lock(l) #define arch_write_lock(l) queued_write_lock(l) #define arch_read_trylock(l) queued_read_trylock(l) #define arch_write_trylock(l) queued_write_trylock(l) #define arch_read_unlock(l) queued_read_unlock(l) #define arch_write_unlock(l) queued_write_unlock(l) #endif /* __ASM_GENERIC_QRWLOCK_H */

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Waiman Long43791.04%350.00%
Pan Xinhui326.67%116.67%
Will Deacon112.29%233.33%
Total480100.00%6100.00%
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