/* * MCS lock defines * * This file contains the main data structure and API definitions of MCS lock. * * The MCS lock (proposed by Mellor-Crummey and Scott) is a simple spin-lock * with the desirable properties of being fair, and with each cpu trying * to acquire the lock spinning on a local variable. * It avoids expensive cache bouncings that common test-and-set spin-lock * implementations incur. */ #ifndef __LINUX_MCS_SPINLOCK_H #define __LINUX_MCS_SPINLOCK_H #include struct mcs_spinlock { struct mcs_spinlock *next; int locked; /* 1 if lock acquired */ int count; /* nesting count, see qspinlock.c */ }; #ifndef arch_mcs_spin_lock_contended /* * Using smp_load_acquire() provides a memory barrier that ensures * subsequent operations happen after the lock is acquired. */ #define arch_mcs_spin_lock_contended(l) \ do { \ while (!(smp_load_acquire(l))) \ cpu_relax(); \ } while (0) #endif #ifndef arch_mcs_spin_unlock_contended /* * smp_store_release() provides a memory barrier to ensure all * operations in the critical section has been completed before * unlocking. */ #define arch_mcs_spin_unlock_contended(l) \ smp_store_release((l), 1) #endif /* * Note: the smp_load_acquire/smp_store_release pair is not * sufficient to form a full memory barrier across * cpus for many architectures (except x86) for mcs_unlock and mcs_lock. * For applications that need a full barrier across multiple cpus * with mcs_unlock and mcs_lock pair, smp_mb__after_unlock_lock() should be * used after mcs_lock. */ /* * In order to acquire the lock, the caller should declare a local node and * pass a reference of the node to this function in addition to the lock. * If the lock has already been acquired, then this will proceed to spin * on this node->locked until the previous lock holder sets the node->locked * in mcs_spin_unlock(). */ static inline void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node) { struct mcs_spinlock *prev; /* Init node */ node->locked = 0; node->next = NULL; /* * We rely on the full barrier with global transitivity implied by the * below xchg() to order the initialization stores above against any * observation of @node. And to provide the ACQUIRE ordering associated * with a LOCK primitive. */ prev = xchg(lock, node); if (likely(prev == NULL)) { /* * Lock acquired, don't need to set node->locked to 1. Threads * only spin on its own node->locked value for lock acquisition. * However, since this thread can immediately acquire the lock * and does not proceed to spin on its own node->locked, this * value won't be used. If a debug mode is needed to * audit lock status, then set node->locked value here. */ return; } WRITE_ONCE(prev->next, node); /* Wait until the lock holder passes the lock down. */ arch_mcs_spin_lock_contended(&node->locked); } /* * Releases the lock. The caller should pass in the corresponding node that * was used to acquire the lock. */ static inline void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node) { struct mcs_spinlock *next = READ_ONCE(node->next); if (likely(!next)) { /* * Release the lock by setting it to NULL */ if (likely(cmpxchg_release(lock, node, NULL) == node)) return; /* Wait until the next pointer is set */ while (!(next = READ_ONCE(node->next))) cpu_relax(); } /* Pass lock to next waiter. */ arch_mcs_spin_unlock_contended(&next->locked); } #endif /* __LINUX_MCS_SPINLOCK_H */ ge='this.form.submit();'>space:mode:

Diffstat (limited to 'net/ieee802154/6lowpan/reassembly.c')