// SPDX-FileCopyrightText: 2009 Mathieu Desnoyers // SPDX-FileCopyrightText: 2009 Paul E. McKenney, IBM Corporation. // // SPDX-License-Identifier: LGPL-2.1-or-later #ifndef _URCU_BP_STATIC_H #define _URCU_BP_STATIC_H /* * Userspace RCU header. * * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU * RELEASE. See urcu.h for linking dynamically with the userspace rcu library. * * IBM's contributions to this file may be relicensed under LGPLv2 or later. */ #include #include #include #include #include #include #include #include #include #include #include #include /* * This code section can only be included in LGPL 2.1 compatible source code. * See below for the function call wrappers which can be used in code meant to * be only linked with the Userspace RCU library. This comes with a small * performance degradation on the read-side due to the added function calls. * This is required to permit relinking with newer versions of the library. */ #ifdef __cplusplus extern "C" { #endif enum urcu_bp_state { URCU_BP_READER_ACTIVE_CURRENT, URCU_BP_READER_ACTIVE_OLD, URCU_BP_READER_INACTIVE, }; /* * The trick here is that URCU_BP_GP_CTR_PHASE must be a multiple of 8 so we can use a * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits. */ #define URCU_BP_GP_COUNT (1UL << 0) /* Use the amount of bits equal to half of the architecture long size */ #define URCU_BP_GP_CTR_PHASE (1UL << (sizeof(long) << 2)) #define URCU_BP_GP_CTR_NEST_MASK (URCU_BP_GP_CTR_PHASE - 1) /* * Used internally by _urcu_bp_read_lock. */ extern void urcu_bp_register(void); struct urcu_bp_gp { /* * Global grace period counter. * Contains the current URCU_BP_GP_CTR_PHASE. * Also has a URCU_BP_GP_COUNT of 1, to accelerate the reader fast path. * Written to only by writer with mutex taken. * Read by both writer and readers. */ unsigned long ctr; } __attribute__((__aligned__(CAA_CACHE_LINE_SIZE))); extern struct urcu_bp_gp urcu_bp_gp; struct urcu_bp_reader { /* Data used by both reader and urcu_bp_synchronize_rcu() */ unsigned long ctr; /* Data used for registry */ struct cds_list_head node __attribute__((__aligned__(CAA_CACHE_LINE_SIZE))); pthread_t tid; int alloc; /* registry entry allocated */ }; /* * Bulletproof version keeps a pointer to a registry not part of the TLS. * Adds a pointer dereference on the read-side, but won't require to unregister * the reader thread. */ extern DECLARE_URCU_TLS(struct urcu_bp_reader *, urcu_bp_reader); #ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER #define urcu_bp_has_sys_membarrier 1 #else extern int urcu_bp_has_sys_membarrier; #endif static inline void urcu_bp_smp_mb_slave(void) { if (caa_likely(urcu_bp_has_sys_membarrier)) cmm_barrier(); else cmm_smp_mb(); } static inline enum urcu_bp_state urcu_bp_reader_state(unsigned long *ctr, cmm_annotate_t *group) { unsigned long v; if (ctr == NULL) return URCU_BP_READER_INACTIVE; /* * Make sure both tests below are done on the same version of *value * to insure consistency. */ v = uatomic_load(ctr); cmm_annotate_group_mem_acquire(group, ctr); if (!(v & URCU_BP_GP_CTR_NEST_MASK)) return URCU_BP_READER_INACTIVE; if (!((v ^ urcu_bp_gp.ctr) & URCU_BP_GP_CTR_PHASE)) return URCU_BP_READER_ACTIVE_CURRENT; return URCU_BP_READER_ACTIVE_OLD; } /* * Helper for _urcu_bp_read_lock(). The format of urcu_bp_gp.ctr (as well as * the per-thread rcu_reader.ctr) has the lower-order bits containing a count of * _urcu_bp_read_lock() nesting, and a single high-order URCU_BP_GP_CTR_PHASE bit * that contains either zero or one. The smp_mb_slave() ensures that the accesses in * _urcu_bp_read_lock() happen before the subsequent read-side critical section. */ static inline void _urcu_bp_read_lock_update(unsigned long tmp) { if (caa_likely(!(tmp & URCU_BP_GP_CTR_NEST_MASK))) { uatomic_store(&URCU_TLS(urcu_bp_reader)->ctr, uatomic_load(&urcu_bp_gp.ctr)); urcu_bp_smp_mb_slave(); } else uatomic_store(&URCU_TLS(urcu_bp_reader)->ctr, tmp + URCU_BP_GP_COUNT); } /* * Enter an RCU read-side critical section. * * The first cmm_barrier() call ensures that the compiler does not reorder * the body of _urcu_bp_read_lock() with a mutex. * * This function and its helper are both less than 10 lines long. The * intent is that this function meets the 10-line criterion in LGPL, * allowing this function to be invoked directly from non-LGPL code. */ static inline void _urcu_bp_read_lock(void) { unsigned long tmp; if (caa_unlikely(!URCU_TLS(urcu_bp_reader))) urcu_bp_register(); /* If not yet registered. */ cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ tmp = URCU_TLS(urcu_bp_reader)->ctr; urcu_assert_debug((tmp & URCU_BP_GP_CTR_NEST_MASK) != URCU_BP_GP_CTR_NEST_MASK); _urcu_bp_read_lock_update(tmp); } /* * Exit an RCU read-side critical section. This function is less than * 10 lines of code, and is intended to be usable by non-LGPL code, as * called out in LGPL. */ static inline void _urcu_bp_read_unlock(void) { unsigned long tmp; unsigned long *ctr = &URCU_TLS(urcu_bp_reader)->ctr; tmp = URCU_TLS(urcu_bp_reader)->ctr; urcu_assert_debug(tmp & URCU_BP_GP_CTR_NEST_MASK); /* Finish using rcu before decrementing the pointer. */ urcu_bp_smp_mb_slave(); cmm_annotate_mem_release(ctr); uatomic_store(ctr, tmp - URCU_BP_GP_COUNT); cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ } /* * Returns whether within a RCU read-side critical section. * * This function is less than 10 lines long. The intent is that this * function meets the 10-line criterion for LGPL, allowing this function * to be invoked directly from non-LGPL code. */ static inline int _urcu_bp_read_ongoing(void) { if (caa_unlikely(!URCU_TLS(urcu_bp_reader))) urcu_bp_register(); /* If not yet registered. */ return URCU_TLS(urcu_bp_reader)->ctr & URCU_BP_GP_CTR_NEST_MASK; } #ifdef __cplusplus } #endif #endif /* _URCU_BP_STATIC_H */