mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-21 13:47:14 +07:00
f9852b74be
The only reason for the current code is to make GCC emit only the "LOCK XADD" instruction on x86 (and not do a pointless extra ADD on the result), do so nicer. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Waiman Long <waiman.long@hpe.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-arch@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
150 lines
4.1 KiB
C
150 lines
4.1 KiB
C
/*
|
|
* Queued read/write locks
|
|
*
|
|
* 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>
|
|
*/
|
|
#include <linux/smp.h>
|
|
#include <linux/bug.h>
|
|
#include <linux/cpumask.h>
|
|
#include <linux/percpu.h>
|
|
#include <linux/hardirq.h>
|
|
#include <asm/qrwlock.h>
|
|
|
|
/*
|
|
* This internal data structure is used for optimizing access to some of
|
|
* the subfields within the atomic_t cnts.
|
|
*/
|
|
struct __qrwlock {
|
|
union {
|
|
atomic_t cnts;
|
|
struct {
|
|
#ifdef __LITTLE_ENDIAN
|
|
u8 wmode; /* Writer mode */
|
|
u8 rcnts[3]; /* Reader counts */
|
|
#else
|
|
u8 rcnts[3]; /* Reader counts */
|
|
u8 wmode; /* Writer mode */
|
|
#endif
|
|
};
|
|
};
|
|
arch_spinlock_t lock;
|
|
};
|
|
|
|
/**
|
|
* rspin_until_writer_unlock - inc reader count & spin until writer is gone
|
|
* @lock : Pointer to queue rwlock structure
|
|
* @writer: Current queue rwlock writer status byte
|
|
*
|
|
* In interrupt context or at the head of the queue, the reader will just
|
|
* increment the reader count & wait until the writer releases the lock.
|
|
*/
|
|
static __always_inline void
|
|
rspin_until_writer_unlock(struct qrwlock *lock, u32 cnts)
|
|
{
|
|
while ((cnts & _QW_WMASK) == _QW_LOCKED) {
|
|
cpu_relax_lowlatency();
|
|
cnts = atomic_read_acquire(&lock->cnts);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* queued_read_lock_slowpath - acquire read lock of a queue rwlock
|
|
* @lock: Pointer to queue rwlock structure
|
|
* @cnts: Current qrwlock lock value
|
|
*/
|
|
void queued_read_lock_slowpath(struct qrwlock *lock, u32 cnts)
|
|
{
|
|
/*
|
|
* Readers come here when they cannot get the lock without waiting
|
|
*/
|
|
if (unlikely(in_interrupt())) {
|
|
/*
|
|
* Readers in interrupt context will get the lock immediately
|
|
* if the writer is just waiting (not holding the lock yet).
|
|
* The rspin_until_writer_unlock() function returns immediately
|
|
* in this case. Otherwise, they will spin (with ACQUIRE
|
|
* semantics) until the lock is available without waiting in
|
|
* the queue.
|
|
*/
|
|
rspin_until_writer_unlock(lock, cnts);
|
|
return;
|
|
}
|
|
atomic_sub(_QR_BIAS, &lock->cnts);
|
|
|
|
/*
|
|
* Put the reader into the wait queue
|
|
*/
|
|
arch_spin_lock(&lock->wait_lock);
|
|
|
|
/*
|
|
* The ACQUIRE semantics of the following spinning code ensure
|
|
* that accesses can't leak upwards out of our subsequent critical
|
|
* section in the case that the lock is currently held for write.
|
|
*/
|
|
cnts = atomic_fetch_add_acquire(_QR_BIAS, &lock->cnts);
|
|
rspin_until_writer_unlock(lock, cnts);
|
|
|
|
/*
|
|
* Signal the next one in queue to become queue head
|
|
*/
|
|
arch_spin_unlock(&lock->wait_lock);
|
|
}
|
|
EXPORT_SYMBOL(queued_read_lock_slowpath);
|
|
|
|
/**
|
|
* queued_write_lock_slowpath - acquire write lock of a queue rwlock
|
|
* @lock : Pointer to queue rwlock structure
|
|
*/
|
|
void queued_write_lock_slowpath(struct qrwlock *lock)
|
|
{
|
|
u32 cnts;
|
|
|
|
/* Put the writer into the wait queue */
|
|
arch_spin_lock(&lock->wait_lock);
|
|
|
|
/* Try to acquire the lock directly if no reader is present */
|
|
if (!atomic_read(&lock->cnts) &&
|
|
(atomic_cmpxchg_acquire(&lock->cnts, 0, _QW_LOCKED) == 0))
|
|
goto unlock;
|
|
|
|
/*
|
|
* Set the waiting flag to notify readers that a writer is pending,
|
|
* or wait for a previous writer to go away.
|
|
*/
|
|
for (;;) {
|
|
struct __qrwlock *l = (struct __qrwlock *)lock;
|
|
|
|
if (!READ_ONCE(l->wmode) &&
|
|
(cmpxchg_relaxed(&l->wmode, 0, _QW_WAITING) == 0))
|
|
break;
|
|
|
|
cpu_relax_lowlatency();
|
|
}
|
|
|
|
/* When no more readers, set the locked flag */
|
|
for (;;) {
|
|
cnts = atomic_read(&lock->cnts);
|
|
if ((cnts == _QW_WAITING) &&
|
|
(atomic_cmpxchg_acquire(&lock->cnts, _QW_WAITING,
|
|
_QW_LOCKED) == _QW_WAITING))
|
|
break;
|
|
|
|
cpu_relax_lowlatency();
|
|
}
|
|
unlock:
|
|
arch_spin_unlock(&lock->wait_lock);
|
|
}
|
|
EXPORT_SYMBOL(queued_write_lock_slowpath);
|