From: Paul E. McKenney Date: Fri, 7 Sep 2012 01:15:53 +0000 (-0400) Subject: Ensure that read-side functions meet 10-line LGPL criterion X-Git-Tag: v0.7.5~2 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=a5a9f428a238e790d6c97299bc214b5cca815cd7;p=userspace-rcu.git Ensure that read-side functions meet 10-line LGPL criterion This commit ensures that all read-side functions meet the 10-line LGPL criterion that permits them to be expanded directly into non-LGPL code, without function-call instructions. It also documents this as the intent. [ paulmck: Spelling fixes called out by Josh Triplett and name change called out by Mathieu Desnoyers (_rcu_read_lock_help() -> _rcu_read_lock_update(). ] [ Mathieu Desnoyers: _rcu_read_unlock_help renamed to _rcu_read_unlock_update_and_wakeup, and spelling fix for preced -> precede. ] Signed-off-by: Paul E. McKenney Signed-off-by: Mathieu Desnoyers --- diff --git a/urcu/static/urcu-bp.h b/urcu/static/urcu-bp.h index e7b2eda..a2f7368 100644 --- a/urcu/static/urcu-bp.h +++ b/urcu/static/urcu-bp.h @@ -6,8 +6,8 @@ * * Userspace RCU header. * - * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking - * dynamically with the userspace rcu library. + * 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. * * Copyright (c) 2009 Mathieu Desnoyers * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. @@ -162,32 +162,48 @@ static inline int rcu_old_gp_ongoing(long *value) ((v ^ rcu_gp_ctr) & RCU_GP_CTR_PHASE); } +/* + * Helper for _rcu_read_lock(). The format of rcu_gp_ctr (as well as + * the per-thread rcu_reader.ctr) has the upper bits containing a count of + * _rcu_read_lock() nesting, and a lower-order bit that contains either zero + * or RCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in + * _rcu_read_lock() happen before the subsequent read-side critical section. + */ +static inline void _rcu_read_lock_update(unsigned long tmp) +{ + if (caa_likely(!(tmp & RCU_GP_CTR_NEST_MASK))) { + _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, _CMM_LOAD_SHARED(rcu_gp_ctr)); + cmm_smp_mb(); + } else + _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, tmp + RCU_GP_COUNT); +} + +/* + * Enter an RCU read-side critical section. + * + * The first cmm_barrier() call ensures that the compiler does not reorder + * the body of _rcu_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 _rcu_read_lock(void) { long tmp; - /* Check if registered */ if (caa_unlikely(!URCU_TLS(rcu_reader))) - rcu_bp_register(); - + rcu_bp_register(); /* If not yet registered. */ cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ tmp = URCU_TLS(rcu_reader)->ctr; - /* - * rcu_gp_ctr is - * RCU_GP_COUNT | (~RCU_GP_CTR_PHASE or RCU_GP_CTR_PHASE) - */ - if (caa_likely(!(tmp & RCU_GP_CTR_NEST_MASK))) { - _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, _CMM_LOAD_SHARED(rcu_gp_ctr)); - /* - * Set active readers count for outermost nesting level before - * accessing the pointer. - */ - cmm_smp_mb(); - } else { - _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, tmp + RCU_GP_COUNT); - } + _rcu_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 _rcu_read_unlock(void) { /* diff --git a/urcu/static/urcu-pointer.h b/urcu/static/urcu-pointer.h index 48dc5bf..4361156 100644 --- a/urcu/static/urcu-pointer.h +++ b/urcu/static/urcu-pointer.h @@ -6,8 +6,8 @@ * * Userspace RCU header. Operations on pointers. * - * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-pointer.h for - * linking dynamically with the userspace rcu library. + * 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. * * Copyright (c) 2009 Mathieu Desnoyers * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. @@ -59,8 +59,11 @@ extern "C" { * addition to forthcoming C++ standard. * * Should match rcu_assign_pointer() or rcu_xchg_pointer(). + * + * This macro is less than 10 lines long. The intent is that this macro + * meets the 10-line criterion in LGPL, allowing this function to be + * expanded directly in non-LGPL code. */ - #define _rcu_dereference(p) ({ \ __typeof__(p) _________p1 = CMM_LOAD_SHARED(p); \ cmm_smp_read_barrier_depends(); \ @@ -73,8 +76,11 @@ extern "C" { * data structure, which can be safely freed after waiting for a quiescent state * using synchronize_rcu(). If fails (unexpected value), returns old (which * should not be freed !). + * + * This macro is less than 10 lines long. The intent is that this macro + * meets the 10-line criterion in LGPL, allowing this function to be + * expanded directly in non-LGPL code. */ - #define _rcu_cmpxchg_pointer(p, old, _new) \ ({ \ __typeof__(*p) _________pold = (old); \ @@ -89,8 +95,11 @@ extern "C" { * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous * pointer to the data structure, which can be safely freed after waiting for a * quiescent state using synchronize_rcu(). + * + * This macro is less than 10 lines long. The intent is that this macro + * meets the 10-line criterion in LGPL, allowing this function to be + * expanded directly in non-LGPL code. */ - #define _rcu_xchg_pointer(p, v) \ ({ \ __typeof__(*p) _________pv = (v); \ @@ -121,8 +130,11 @@ extern "C" { * data structure before its publication. * * Should match rcu_dereference_pointer(). + * + * This macro is less than 10 lines long. The intent is that this macro + * meets the 10-line criterion in LGPL, allowing this function to be + * expanded directly in non-LGPL code. */ - #define _rcu_assign_pointer(p, v) _rcu_set_pointer(&(p), v) #ifdef __cplusplus diff --git a/urcu/static/urcu-qsbr.h b/urcu/static/urcu-qsbr.h index 22908a4..5580092 100644 --- a/urcu/static/urcu-qsbr.h +++ b/urcu/static/urcu-qsbr.h @@ -6,8 +6,8 @@ * * Userspace RCU QSBR header. * - * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-qsbr.h for linking - * dynamically with the userspace rcu QSBR library. + * 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. * * Copyright (c) 2009 Mathieu Desnoyers * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. @@ -157,15 +157,36 @@ static inline int rcu_gp_ongoing(unsigned long *ctr) return v && (v != rcu_gp_ctr); } +/* + * Enter an 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 void _rcu_read_lock(void) { rcu_assert(URCU_TLS(rcu_reader).ctr); } +/* + * Exit an 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 void _rcu_read_unlock(void) { } +/* + * Inform RCU of a quiescent state. + * + * 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 void _rcu_quiescent_state(void) { cmm_smp_mb(); @@ -175,6 +196,14 @@ static inline void _rcu_quiescent_state(void) cmm_smp_mb(); } +/* + * Take a thread offline, prohibiting it from entering further RCU + * read-side critical sections. + * + * 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 void _rcu_thread_offline(void) { cmm_smp_mb(); @@ -184,6 +213,14 @@ static inline void _rcu_thread_offline(void) cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ } +/* + * Bring a thread online, allowing it to once again enter RCU + * read-side critical sections. + * + * 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 void _rcu_thread_online(void) { cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ diff --git a/urcu/static/urcu.h b/urcu/static/urcu.h index f27f8b6..c517693 100644 --- a/urcu/static/urcu.h +++ b/urcu/static/urcu.h @@ -6,8 +6,8 @@ * * Userspace RCU header. * - * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking - * dynamically with the userspace rcu library. + * 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. * * Copyright (c) 2009 Mathieu Desnoyers * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. @@ -252,46 +252,71 @@ static inline int rcu_gp_ongoing(unsigned long *ctr) ((v ^ rcu_gp_ctr) & RCU_GP_CTR_PHASE); } -static inline void _rcu_read_lock(void) +/* + * Helper for _rcu_read_lock(). The format of rcu_gp_ctr (as well as + * the per-thread rcu_reader.ctr) has the upper bits containing a count of + * _rcu_read_lock() nesting, and a lower-order bit that contains either zero + * or RCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in + * _rcu_read_lock() happen before the subsequent read-side critical section. + */ +static inline void _rcu_read_lock_update(unsigned long tmp) { - unsigned long tmp; - - cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ - tmp = URCU_TLS(rcu_reader).ctr; - /* - * rcu_gp_ctr is - * RCU_GP_COUNT | (~RCU_GP_CTR_PHASE or RCU_GP_CTR_PHASE) - */ if (caa_likely(!(tmp & RCU_GP_CTR_NEST_MASK))) { _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, _CMM_LOAD_SHARED(rcu_gp_ctr)); - /* - * Set active readers count for outermost nesting level before - * accessing the pointer. See smp_mb_master(). - */ smp_mb_slave(RCU_MB_GROUP); - } else { + } else _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, tmp + RCU_GP_COUNT); - } } -static inline void _rcu_read_unlock(void) +/* + * Enter an RCU read-side critical section. + * + * The first cmm_barrier() call ensures that the compiler does not reorder + * the body of _rcu_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 _rcu_read_lock(void) { unsigned long tmp; + cmm_barrier(); tmp = URCU_TLS(rcu_reader).ctr; - /* - * Finish using rcu before decrementing the pointer. - * See smp_mb_master(). - */ + _rcu_read_lock_update(tmp); +} + +/* + * This is a helper function for _rcu_read_unlock(). + * + * The first smp_mb_slave() call ensures that the critical section is + * seen to precede the store to rcu_reader.ctr. + * The second smp_mb_slave() call ensures that we write to rcu_reader.ctr + * before reading the update-side futex. + */ +static inline void _rcu_read_unlock_update_and_wakeup(unsigned long tmp) +{ if (caa_likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) { smp_mb_slave(RCU_MB_GROUP); _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, URCU_TLS(rcu_reader).ctr - RCU_GP_COUNT); - /* write URCU_TLS(rcu_reader).ctr before read futex */ smp_mb_slave(RCU_MB_GROUP); wake_up_gp(); - } else { + } else _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, URCU_TLS(rcu_reader).ctr - RCU_GP_COUNT); - } +} + +/* + * Exit an RCU read-side crtical section. Both this function and its + * helper are smaller than 10 lines of code, and are intended to be + * usable by non-LGPL code, as called out in LGPL. + */ +static inline void _rcu_read_unlock(void) +{ + unsigned long tmp; + + tmp = URCU_TLS(rcu_reader).ctr; + _rcu_read_unlock_update_and_wakeup(tmp); cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ }