/* * 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 */ #include #include #include #include #include #include /* * 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(); 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(); } /* 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(); } unlock: arch_spin_unlock(&lock->wait_lock); } EXPORT_SYMBOL(queued_write_lock_slowpath); value='2'>2space:mode:
Diffstat (limited to 'include/net/netns/mib.h')