1 // SPDX-FileCopyrightText: 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
2 // SPDX-FileCopyrightText: 2009 Paul E. McKenney, IBM Corporation.
4 // SPDX-License-Identifier: LGPL-2.1-or-later
6 #ifndef _URCU_MEMB_STATIC_H
7 #define _URCU_MEMB_STATIC_H
10 * Userspace RCU header.
12 * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
13 * RELEASE. See urcu.h for linking dynamically with the userspace rcu library.
15 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
23 #include <urcu/annotate.h>
24 #include <urcu/debug.h>
25 #include <urcu/config.h>
26 #include <urcu/compiler.h>
27 #include <urcu/arch.h>
28 #include <urcu/system.h>
29 #include <urcu/uatomic.h>
30 #include <urcu/list.h>
31 #include <urcu/futex.h>
32 #include <urcu/tls-compat.h>
33 #include <urcu/static/urcu-common.h>
40 * This code section can only be included in LGPL 2.1 compatible source code.
41 * See below for the function call wrappers which can be used in code meant to
42 * be only linked with the Userspace RCU library. This comes with a small
43 * performance degradation on the read-side due to the added function calls.
44 * This is required to permit relinking with newer versions of the library.
48 * Slave barriers are only guaranteed to be ordered wrt master barriers.
50 * The pair ordering is detailed as (O: ordered, X: not ordered) :
56 #ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER
57 #define urcu_memb_has_sys_membarrier 1
59 extern int urcu_memb_has_sys_membarrier
;
62 static inline void urcu_memb_smp_mb_slave(void)
64 if (caa_likely(urcu_memb_has_sys_membarrier
))
70 extern struct urcu_gp urcu_memb_gp
;
72 extern DECLARE_URCU_TLS(struct urcu_reader
, urcu_memb_reader
);
75 * Helper for _rcu_read_lock(). The format of urcu_memb_gp.ctr (as well as
76 * the per-thread rcu_reader.ctr) has the lower-order bits containing a count of
77 * _rcu_read_lock() nesting, and a single high-order URCU_BP_GP_CTR_PHASE bit
78 * that contains either zero or one. The smp_mb_slave() ensures that the accesses in
79 * _rcu_read_lock() happen before the subsequent read-side critical section.
81 static inline void _urcu_memb_read_lock_update(unsigned long tmp
)
83 unsigned long *ctr
= &URCU_TLS(urcu_memb_reader
).ctr
;
85 if (caa_likely(!(tmp
& URCU_GP_CTR_NEST_MASK
))) {
86 unsigned long *pgctr
= &urcu_memb_gp
.ctr
;
87 unsigned long gctr
= uatomic_load(pgctr
, CMM_RELAXED
);
89 /* Paired with following mb slave. */
90 cmm_annotate_mem_acquire(pgctr
);
91 uatomic_store(ctr
, gctr
, CMM_RELAXED
);
93 urcu_memb_smp_mb_slave();
95 uatomic_store(ctr
, tmp
+ URCU_GP_COUNT
, CMM_RELAXED
);
100 * Enter an RCU read-side critical section.
102 * The first cmm_barrier() call ensures that the compiler does not reorder
103 * the body of _rcu_read_lock() with a mutex.
105 * This function and its helper are both less than 10 lines long. The
106 * intent is that this function meets the 10-line criterion in LGPL,
107 * allowing this function to be invoked directly from non-LGPL code.
109 static inline void _urcu_memb_read_lock(void)
113 urcu_assert_debug(URCU_TLS(urcu_memb_reader
).registered
);
115 tmp
= URCU_TLS(urcu_memb_reader
).ctr
;
116 urcu_assert_debug((tmp
& URCU_GP_CTR_NEST_MASK
) != URCU_GP_CTR_NEST_MASK
);
117 _urcu_memb_read_lock_update(tmp
);
121 * This is a helper function for _rcu_read_unlock().
123 * The first smp_mb_slave() call ensures that the critical section is
124 * seen to precede the store to rcu_reader.ctr.
125 * The second smp_mb_slave() call ensures that we write to rcu_reader.ctr
126 * before reading the update-side futex.
128 static inline void _urcu_memb_read_unlock_update_and_wakeup(unsigned long tmp
)
130 unsigned long *ctr
= &URCU_TLS(urcu_memb_reader
).ctr
;
132 if (caa_likely((tmp
& URCU_GP_CTR_NEST_MASK
) == URCU_GP_COUNT
)) {
133 urcu_memb_smp_mb_slave();
134 cmm_annotate_mem_release(ctr
);
135 uatomic_store(ctr
, tmp
- URCU_GP_COUNT
, CMM_RELAXED
);
136 urcu_memb_smp_mb_slave();
137 urcu_common_wake_up_gp(&urcu_memb_gp
);
139 uatomic_store(ctr
, tmp
- URCU_GP_COUNT
, CMM_RELAXED
);
144 * Exit an RCU read-side critical section. Both this function and its
145 * helper are smaller than 10 lines of code, and are intended to be
146 * usable by non-LGPL code, as called out in LGPL.
148 static inline void _urcu_memb_read_unlock(void)
152 urcu_assert_debug(URCU_TLS(urcu_memb_reader
).registered
);
153 tmp
= URCU_TLS(urcu_memb_reader
).ctr
;
154 urcu_assert_debug(tmp
& URCU_GP_CTR_NEST_MASK
);
155 _urcu_memb_read_unlock_update_and_wakeup(tmp
);
156 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
160 * Returns whether within a RCU read-side critical section.
162 * This function is less than 10 lines long. The intent is that this
163 * function meets the 10-line criterion for LGPL, allowing this function
164 * to be invoked directly from non-LGPL code.
166 static inline int _urcu_memb_read_ongoing(void)
168 return URCU_TLS(urcu_memb_reader
).ctr
& URCU_GP_CTR_NEST_MASK
;
175 #endif /* _URCU_MEMB_STATIC_H */