From 4e3274705324c695f56b3e1c194cd99b76eeea0f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 7 Jun 2017 16:02:24 -0700 Subject: init_task: Remove redundant INIT_TASK_RCU_TREE_PREEMPT() macro Back in the dim distant past, the task_struct structure's RCU-related fields optionally included those needed for CONFIG_RCU_BOOST, even in CONFIG_PREEMPT_RCU builds. The INIT_TASK_RCU_TREE_PREEMPT() macro was used to provide initializers for those optional CONFIG_RCU_BOOST fields. However, the CONFIG_RCU_BOOST fields are now included unconditionally in CONFIG_PREEMPT_RCU builds, so there is no longer any need fro the INIT_TASK_RCU_TREE_PREEMPT() macro. This commit therefore removes it in favor of initializing the ->rcu_blocked_node field directly in the INIT_TASK_RCU_PREEMPT() macro. Signed-off-by: Paul E. McKenney --- include/linux/init_task.h | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-) (limited to 'include') diff --git a/include/linux/init_task.h b/include/linux/init_task.h index a2f6707e9fc0..0e849715e5be 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -125,18 +125,12 @@ extern struct group_info init_groups; #define INIT_IDS #endif -#ifdef CONFIG_PREEMPT_RCU -#define INIT_TASK_RCU_TREE_PREEMPT() \ - .rcu_blocked_node = NULL, -#else -#define INIT_TASK_RCU_TREE_PREEMPT(tsk) -#endif #ifdef CONFIG_PREEMPT_RCU #define INIT_TASK_RCU_PREEMPT(tsk) \ .rcu_read_lock_nesting = 0, \ .rcu_read_unlock_special.s = 0, \ .rcu_node_entry = LIST_HEAD_INIT(tsk.rcu_node_entry), \ - INIT_TASK_RCU_TREE_PREEMPT() + .rcu_blocked_node = NULL, #else #define INIT_TASK_RCU_PREEMPT(tsk) #endif -- cgit v1.2.3 From 825c5bd2fd47d30148db15fc121216c483682b01 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 26 May 2017 16:16:40 -0700 Subject: srcu: Move rcu_scheduler_starting() from Tiny RCU to Tiny SRCU Other than lockdep support, Tiny RCU has no need for the scheduler status. However, Tiny SRCU will need this to control boot-time behavior independent of lockdep. Therefore, this commit moves rcu_scheduler_starting() from kernel/rcu/tiny_plugin.h to kernel/rcu/srcutiny.c. This in turn allows the complete removal of kernel/rcu/tiny_plugin.h. Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 1 + include/linux/rcutiny.h | 8 +++----- kernel/rcu/srcutiny.c | 8 ++++++++ kernel/rcu/tiny.c | 2 -- kernel/rcu/tiny_plugin.h | 47 ----------------------------------------------- 5 files changed, 12 insertions(+), 54 deletions(-) delete mode 100644 kernel/rcu/tiny_plugin.h (limited to 'include') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index f816fc72b51e..55c29e1650b9 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -105,6 +105,7 @@ static inline int rcu_preempt_depth(void) /* Internal to kernel */ void rcu_init(void); +extern int rcu_scheduler_active __read_mostly; void rcu_sched_qs(void); void rcu_bh_qs(void); void rcu_check_callbacks(int user); diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 5becbbccb998..b3dbf9502fd0 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -116,13 +116,11 @@ static inline void rcu_irq_exit_irqson(void) { } static inline void rcu_irq_enter_irqson(void) { } static inline void rcu_irq_exit(void) { } static inline void exit_rcu(void) { } - -#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) -extern int rcu_scheduler_active __read_mostly; +#ifdef CONFIG_SRCU void rcu_scheduler_starting(void); -#else /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) */ +#else /* #ifndef CONFIG_SRCU */ static inline void rcu_scheduler_starting(void) { } -#endif /* #else #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) */ +#endif /* #else #ifndef CONFIG_SRCU */ static inline void rcu_end_inkernel_boot(void) { } static inline bool rcu_is_watching(void) { return true; } diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c index 1a1c1047d2ed..76ac5f50b2c7 100644 --- a/kernel/rcu/srcutiny.c +++ b/kernel/rcu/srcutiny.c @@ -33,6 +33,8 @@ #include "rcu_segcblist.h" #include "rcu.h" +int rcu_scheduler_active __read_mostly; + static int init_srcu_struct_fields(struct srcu_struct *sp) { sp->srcu_lock_nesting[0] = 0; @@ -193,3 +195,9 @@ void synchronize_srcu(struct srcu_struct *sp) destroy_rcu_head_on_stack(&rs.head); } EXPORT_SYMBOL_GPL(synchronize_srcu); + +/* Lockdep diagnostics. */ +void __init rcu_scheduler_starting(void) +{ + rcu_scheduler_active = RCU_SCHEDULER_RUNNING; +} diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c index f8488965250f..a64eee0db39e 100644 --- a/kernel/rcu/tiny.c +++ b/kernel/rcu/tiny.c @@ -56,8 +56,6 @@ static struct rcu_ctrlblk rcu_bh_ctrlblk = { .curtail = &rcu_bh_ctrlblk.rcucblist, }; -#include "tiny_plugin.h" - void rcu_barrier_bh(void) { wait_rcu_gp(call_rcu_bh); diff --git a/kernel/rcu/tiny_plugin.h b/kernel/rcu/tiny_plugin.h deleted file mode 100644 index f0a01b2a3062..000000000000 --- a/kernel/rcu/tiny_plugin.h +++ /dev/null @@ -1,47 +0,0 @@ -/* - * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition - * Internal non-public definitions that provide either classic - * or preemptible semantics. - * - * 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. - * - * You should have received a copy of the GNU General Public License - * along with this program; if not, you can access it online at - * http://www.gnu.org/licenses/gpl-2.0.html. - * - * Copyright (c) 2010 Linaro - * - * Author: Paul E. McKenney - */ - -#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) -#include - -int rcu_scheduler_active __read_mostly; -EXPORT_SYMBOL_GPL(rcu_scheduler_active); - -/* - * During boot, we forgive RCU lockdep issues. After this function is - * invoked, we start taking RCU lockdep issues seriously. Note that unlike - * Tree RCU, Tiny RCU transitions directly from RCU_SCHEDULER_INACTIVE - * to RCU_SCHEDULER_RUNNING, skipping the RCU_SCHEDULER_INIT stage. - * The reason for this is that Tiny RCU does not need kthreads, so does - * not have to care about the fact that the scheduler is half-initialized - * at a certain phase of the boot process. Unless SRCU is in the mix. - */ -void __init rcu_scheduler_starting(void) -{ - WARN_ON(nr_context_switches() > 0); - rcu_scheduler_active = IS_ENABLED(CONFIG_SRCU) - ? RCU_SCHEDULER_INIT : RCU_SCHEDULER_RUNNING; -} - -#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) */ -- cgit v1.2.3 From 0d8a1e831e21d955af68f4ae5658b58b7ec25557 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 15 Jun 2017 17:06:38 -0700 Subject: srcu: Make process_srcu() be static The function process_srcu() is not invoked outside of srcutree.c, so this commit makes it static and drops the EXPORT_SYMBOL_GPL(). Signed-off-by: Paul E. McKenney --- include/linux/srcutree.h | 2 -- kernel/rcu/srcutree.c | 4 ++-- 2 files changed, 2 insertions(+), 4 deletions(-) (limited to 'include') diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index 42973f787e7e..a026a9493bde 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -104,8 +104,6 @@ struct srcu_struct { #define SRCU_STATE_SCAN1 1 #define SRCU_STATE_SCAN2 2 -void process_srcu(struct work_struct *work); - #define __SRCU_STRUCT_INIT(name) \ { \ .sda = &name##_srcu_data, \ diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index d0ca524bf042..94bd6ed43ea3 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -51,6 +51,7 @@ module_param(counter_wrap_check, ulong, 0444); static void srcu_invoke_callbacks(struct work_struct *work); static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay); +static void process_srcu(struct work_struct *work); /* * Initialize SRCU combining tree. Note that statically allocated @@ -1194,7 +1195,7 @@ static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay) /* * This is the work-queue function that handles SRCU grace periods. */ -void process_srcu(struct work_struct *work) +static void process_srcu(struct work_struct *work) { struct srcu_struct *sp; @@ -1203,7 +1204,6 @@ void process_srcu(struct work_struct *work) srcu_advance_state(sp); srcu_reschedule(sp, srcu_get_delay(sp)); } -EXPORT_SYMBOL_GPL(process_srcu); void srcutorture_get_gp_data(enum rcutorture_type test_type, struct srcu_struct *sp, int *flags, -- cgit v1.2.3 From 115a1a5285664f1931c30457081b4ae1e648f1f9 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 22 May 2017 13:31:03 -0700 Subject: rcutorture: Move SRCU status printing to SRCU implementations This commit gets rid of some ugly #ifdefs in rcutorture.c by moving the SRCU status printing to the SRCU implementations. Signed-off-by: Paul E. McKenney --- include/linux/srcutiny.h | 13 +++++++++++++ include/linux/srcutree.h | 1 + kernel/rcu/rcutorture.c | 39 +-------------------------------------- kernel/rcu/srcutree.c | 34 ++++++++++++++++++++++++++++++++++ 4 files changed, 49 insertions(+), 38 deletions(-) (limited to 'include') diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h index cfbfc540cafc..261471f407a5 100644 --- a/include/linux/srcutiny.h +++ b/include/linux/srcutiny.h @@ -87,4 +87,17 @@ static inline void srcu_barrier(struct srcu_struct *sp) synchronize_srcu(sp); } +/* Defined here to avoid size increase for non-torture kernels. */ +static inline void srcu_torture_stats_print(struct srcu_struct *sp, + char *tt, char *tf) +{ + int idx; + + idx = READ_ONCE(sp->srcu_idx) & 0x1; + pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n", + tt, tf, idx, + READ_ONCE(sp->srcu_lock_nesting[!idx]), + READ_ONCE(sp->srcu_lock_nesting[idx])); +} + #endif diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index 42973f787e7e..7886356bdc84 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -141,5 +141,6 @@ void process_srcu(struct work_struct *work); void synchronize_srcu_expedited(struct srcu_struct *sp); void srcu_barrier(struct srcu_struct *sp); +void srcu_torture_stats_print(struct srcu_struct *sp, char *tt, char *tf); #endif diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index b8f7f8ce8575..aedc8f2ad955 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -561,44 +561,7 @@ static void srcu_torture_barrier(void) static void srcu_torture_stats(void) { - int __maybe_unused cpu; - int idx; - -#ifdef CONFIG_TREE_SRCU - idx = srcu_ctlp->srcu_idx & 0x1; - pr_alert("%s%s Tree SRCU per-CPU(idx=%d):", - torture_type, TORTURE_FLAG, idx); - for_each_possible_cpu(cpu) { - unsigned long l0, l1; - unsigned long u0, u1; - long c0, c1; - struct srcu_data *counts; - - counts = per_cpu_ptr(srcu_ctlp->sda, cpu); - u0 = counts->srcu_unlock_count[!idx]; - u1 = counts->srcu_unlock_count[idx]; - - /* - * Make sure that a lock is always counted if the corresponding - * unlock is counted. - */ - smp_rmb(); - - l0 = counts->srcu_lock_count[!idx]; - l1 = counts->srcu_lock_count[idx]; - - c0 = l0 - u0; - c1 = l1 - u1; - pr_cont(" %d(%ld,%ld)", cpu, c0, c1); - } - pr_cont("\n"); -#elif defined(CONFIG_TINY_SRCU) - idx = READ_ONCE(srcu_ctlp->srcu_idx) & 0x1; - pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n", - torture_type, TORTURE_FLAG, idx, - READ_ONCE(srcu_ctlp->srcu_lock_nesting[!idx]), - READ_ONCE(srcu_ctlp->srcu_lock_nesting[idx])); -#endif + srcu_torture_stats_print(srcu_ctlp, torture_type, TORTURE_FLAG); } static void srcu_torture_synchronize_expedited(void) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index d0ca524bf042..8f6fd11c338a 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -1217,6 +1217,40 @@ void srcutorture_get_gp_data(enum rcutorture_type test_type, } EXPORT_SYMBOL_GPL(srcutorture_get_gp_data); +void srcu_torture_stats_print(struct srcu_struct *sp, char *tt, char *tf) +{ + int cpu; + int idx; + + idx = sp->srcu_idx & 0x1; + pr_alert("%s%s Tree SRCU per-CPU(idx=%d):", tt, tf, idx); + for_each_possible_cpu(cpu) { + unsigned long l0, l1; + unsigned long u0, u1; + long c0, c1; + struct srcu_data *counts; + + counts = per_cpu_ptr(sp->sda, cpu); + u0 = counts->srcu_unlock_count[!idx]; + u1 = counts->srcu_unlock_count[idx]; + + /* + * Make sure that a lock is always counted if the corresponding + * unlock is counted. + */ + smp_rmb(); + + l0 = counts->srcu_lock_count[!idx]; + l1 = counts->srcu_lock_count[idx]; + + c0 = l0 - u0; + c1 = l1 - u1; + pr_cont(" %d(%ld,%ld)", cpu, c0, c1); + } + pr_cont("\n"); +} +EXPORT_SYMBOL_GPL(srcu_torture_stats_print); + static int __init srcu_bootup_announce(void) { pr_info("Hierarchical SRCU implementation.\n"); -- cgit v1.2.3 From b3c983142d4584c9d506b1ed31b65f4292b4aea8 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 6 Jun 2017 16:39:00 -0700 Subject: rcutorture: Place event-traced strings into trace buffer Strings used in event tracing need to be specially handled, for example, being copied to the trace buffer instead of being pointed to by the trace buffer. Although the TPS() macro can be used to "launder" pointed-to strings, this might not be all that effective within a loadable module. This commit therefore copies rcutorture's strings to the trace buffer. Signed-off-by: Paul E. McKenney Cc: Steven Rostedt --- include/trace/events/rcu.h | 7 +++++-- kernel/rcu/rcutorture.c | 2 +- tools/testing/selftests/rcutorture/configs/rcu/BUSTED.boot | 2 +- 3 files changed, 7 insertions(+), 4 deletions(-) (limited to 'include') diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h index 91dc089d65b7..e91ae1f2290d 100644 --- a/include/trace/events/rcu.h +++ b/include/trace/events/rcu.h @@ -703,6 +703,7 @@ TRACE_EVENT(rcu_batch_end, * at the beginning and end of the read, respectively. Note that the * callback address can be NULL. */ +#define RCUTORTURENAME_LEN 8 TRACE_EVENT(rcu_torture_read, TP_PROTO(const char *rcutorturename, struct rcu_head *rhp, @@ -711,7 +712,7 @@ TRACE_EVENT(rcu_torture_read, TP_ARGS(rcutorturename, rhp, secs, c_old, c), TP_STRUCT__entry( - __field(const char *, rcutorturename) + __field(char, rcutorturename[RCUTORTURENAME_LEN]) __field(struct rcu_head *, rhp) __field(unsigned long, secs) __field(unsigned long, c_old) @@ -719,7 +720,9 @@ TRACE_EVENT(rcu_torture_read, ), TP_fast_assign( - __entry->rcutorturename = rcutorturename; + strncpy(__entry->rcutorturename, rcutorturename, + RCUTORTURENAME_LEN); + __entry->rcutorturename[RCUTORTURENAME_LEN - 1] = 0; __entry->rhp = rhp; __entry->secs = secs; __entry->c_old = c_old; diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index 8d59c82bec0b..b48d2107f176 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -496,7 +496,7 @@ static struct rcu_torture_ops rcu_busted_ops = { .fqs = NULL, .stats = NULL, .irq_capable = 1, - .name = "rcu_busted" + .name = "busted" }; /* diff --git a/tools/testing/selftests/rcutorture/configs/rcu/BUSTED.boot b/tools/testing/selftests/rcutorture/configs/rcu/BUSTED.boot index 6804f9dcfc1b..be7728db42fd 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/BUSTED.boot +++ b/tools/testing/selftests/rcutorture/configs/rcu/BUSTED.boot @@ -1 +1 @@ -rcutorture.torture_type=rcu_busted +rcutorture.torture_type=busted -- cgit v1.2.3 From 931ab4a5ce2d93cb434dc7fc067a702117453b13 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 25 Jul 2017 09:59:08 -0700 Subject: atomics: Revert addition of comment header to spin_unlock_wait() There is still considerable confusion as to the semantics of spin_unlock_wait(), but there seems to be universal agreement that it is not that of a lock/unlock pair. This commit therefore removes the comment added by 6016ffc3874d ("atomics: Add header comment so spin_unlock_wait()") in order to prevent at least that flavor of confusion. Signed-off-by: Paul E. McKenney --- include/linux/spinlock.h | 20 -------------------- 1 file changed, 20 deletions(-) (limited to 'include') diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h index d9510e8522d4..59248dcc6ef3 100644 --- a/include/linux/spinlock.h +++ b/include/linux/spinlock.h @@ -369,26 +369,6 @@ static __always_inline int spin_trylock_irq(spinlock_t *lock) raw_spin_trylock_irqsave(spinlock_check(lock), flags); \ }) -/** - * spin_unlock_wait - Interpose between successive critical sections - * @lock: the spinlock whose critical sections are to be interposed. - * - * Semantically this is equivalent to a spin_lock() immediately - * followed by a spin_unlock(). However, most architectures have - * more efficient implementations in which the spin_unlock_wait() - * cannot block concurrent lock acquisition, and in some cases - * where spin_unlock_wait() does not write to the lock variable. - * Nevertheless, spin_unlock_wait() can have high overhead, so if - * you feel the need to use it, please check to see if there is - * a better way to get your job done. - * - * The ordering guarantees provided by spin_unlock_wait() are: - * - * 1. All accesses preceding the spin_unlock_wait() happen before - * any accesses in later critical sections for this same lock. - * 2. All accesses following the spin_unlock_wait() happen after - * any accesses in earlier critical sections for this same lock. - */ static __always_inline void spin_unlock_wait(spinlock_t *lock) { raw_spin_unlock_wait(&lock->rlock); -- cgit v1.2.3 From 7e42776d5ed1fe9a941ed8876c5d15cd7cf5d89f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 25 May 2017 08:05:00 -0700 Subject: rcu: Drive TASKS_RCU directly off of PREEMPT The actual use of TASKS_RCU is only when PREEMPT, otherwise RCU-sched is used instead. This commit therefore makes synchronize_rcu_tasks() and call_rcu_tasks() available always, but mapped to synchronize_sched() and call_rcu_sched(), respectively, when !PREEMPT. This approach also allows some #ifdefs to be removed from rcutorture. Reported-by: Ingo Molnar Signed-off-by: Paul E. McKenney Reviewed-by: Masami Hiramatsu Acked-by: Ingo Molnar --- include/linux/rcupdate.h | 6 ++++-- kernel/rcu/Kconfig | 3 +-- kernel/rcu/rcutorture.c | 17 +---------------- .../selftests/rcutorture/doc/TREE_RCU-kconfig.txt | 2 +- 4 files changed, 7 insertions(+), 21 deletions(-) (limited to 'include') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index f816fc72b51e..c3f380befdd7 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -58,8 +58,6 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func); void call_rcu_bh(struct rcu_head *head, rcu_callback_t func); void call_rcu_sched(struct rcu_head *head, rcu_callback_t func); void synchronize_sched(void); -void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); -void synchronize_rcu_tasks(void); void rcu_barrier_tasks(void); #ifdef CONFIG_PREEMPT_RCU @@ -176,10 +174,14 @@ extern struct srcu_struct tasks_rcu_exit_srcu; rcu_all_qs(); \ rcu_note_voluntary_context_switch_lite(t); \ } while (0) +void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); +void synchronize_rcu_tasks(void); #else /* #ifdef CONFIG_TASKS_RCU */ #define TASKS_RCU(x) do { } while (0) #define rcu_note_voluntary_context_switch_lite(t) do { } while (0) #define rcu_note_voluntary_context_switch(t) rcu_all_qs() +#define call_rcu_tasks call_rcu_sched +#define synchronize_rcu_tasks synchronize_sched #endif /* #else #ifdef CONFIG_TASKS_RCU */ /** diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index be90c945063f..9210379c0353 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -69,8 +69,7 @@ config TREE_SRCU This option selects the full-fledged version of SRCU. config TASKS_RCU - bool - default n + def_bool PREEMPT select SRCU help This option enables a task-based RCU implementation that uses diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index b8f7f8ce8575..b284c861a511 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -696,8 +696,6 @@ static struct rcu_torture_ops sched_ops = { .name = "sched" }; -#ifdef CONFIG_TASKS_RCU - /* * Definitions for RCU-tasks torture testing. */ @@ -735,24 +733,11 @@ static struct rcu_torture_ops tasks_ops = { .name = "tasks" }; -#define RCUTORTURE_TASKS_OPS &tasks_ops, - static bool __maybe_unused torturing_tasks(void) { return cur_ops == &tasks_ops; } -#else /* #ifdef CONFIG_TASKS_RCU */ - -#define RCUTORTURE_TASKS_OPS - -static bool __maybe_unused torturing_tasks(void) -{ - return false; -} - -#endif /* #else #ifdef CONFIG_TASKS_RCU */ - /* * RCU torture priority-boost testing. Runs one real-time thread per * CPU for moderate bursts, repeatedly registering RCU callbacks and @@ -1749,7 +1734,7 @@ rcu_torture_init(void) int firsterr = 0; static struct rcu_torture_ops *torture_ops[] = { &rcu_ops, &rcu_bh_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops, - &sched_ops, RCUTORTURE_TASKS_OPS + &sched_ops, &tasks_ops, }; if (!torture_init_begin(torture_type, verbose, &torture_runnable)) diff --git a/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt b/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt index 9ad3f89c8dc7..af6fca03602f 100644 --- a/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt +++ b/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt @@ -69,11 +69,11 @@ CONFIG_RCU_TORTURE_TEST_RUNNABLE CONFIG_PREEMPT_RCU CONFIG_TREE_RCU CONFIG_TINY_RCU +CONFIG_TASKS_RCU These are controlled by CONFIG_PREEMPT and/or CONFIG_SMP. CONFIG_SRCU -CONFIG_TASKS_RCU Selected by CONFIG_RCU_TORTURE_TEST, so cannot disable. -- cgit v1.2.3 From ccdd29ffffa7246cb359b9408772858a15fc4ea5 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 25 May 2017 08:51:48 -0700 Subject: rcu: Create reasonable API for do_exit() TASKS_RCU processing Currently, the exit-time support for TASKS_RCU is open-coded in do_exit(). This commit creates exit_tasks_rcu_start() and exit_tasks_rcu_finish() APIs for do_exit() use. This has the benefit of confining the use of the tasks_rcu_exit_srcu variable to one file, allowing it to become static. Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 7 ++++--- include/linux/sched.h | 5 +++-- kernel/exit.c | 7 ++----- kernel/rcu/update.c | 18 +++++++++++++++++- 4 files changed, 26 insertions(+), 11 deletions(-) (limited to 'include') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index c3f380befdd7..ce9d21923d75 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -162,8 +162,6 @@ static inline void rcu_init_nohz(void) { } * macro rather than an inline function to avoid #include hell. */ #ifdef CONFIG_TASKS_RCU -#define TASKS_RCU(x) x -extern struct srcu_struct tasks_rcu_exit_srcu; #define rcu_note_voluntary_context_switch_lite(t) \ do { \ if (READ_ONCE((t)->rcu_tasks_holdout)) \ @@ -176,12 +174,15 @@ extern struct srcu_struct tasks_rcu_exit_srcu; } while (0) void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); void synchronize_rcu_tasks(void); +void exit_tasks_rcu_start(void); +void exit_tasks_rcu_finish(void); #else /* #ifdef CONFIG_TASKS_RCU */ -#define TASKS_RCU(x) do { } while (0) #define rcu_note_voluntary_context_switch_lite(t) do { } while (0) #define rcu_note_voluntary_context_switch(t) rcu_all_qs() #define call_rcu_tasks call_rcu_sched #define synchronize_rcu_tasks synchronize_sched +static inline void exit_tasks_rcu_start(void) { } +static inline void exit_tasks_rcu_finish(void) { } #endif /* #else #ifdef CONFIG_TASKS_RCU */ /** diff --git a/include/linux/sched.h b/include/linux/sched.h index 8337e2db0bb2..e4c38809a09e 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -589,9 +589,10 @@ struct task_struct { #ifdef CONFIG_TASKS_RCU unsigned long rcu_tasks_nvcsw; - bool rcu_tasks_holdout; - struct list_head rcu_tasks_holdout_list; + u8 rcu_tasks_holdout; + u8 rcu_tasks_idx; int rcu_tasks_idle_cpu; + struct list_head rcu_tasks_holdout_list; #endif /* #ifdef CONFIG_TASKS_RCU */ struct sched_info sched_info; diff --git a/kernel/exit.c b/kernel/exit.c index c5548faa9f37..d297c525f188 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -764,7 +764,6 @@ void __noreturn do_exit(long code) { struct task_struct *tsk = current; int group_dead; - TASKS_RCU(int tasks_rcu_i); profile_task_exit(tsk); kcov_task_exit(tsk); @@ -881,9 +880,7 @@ void __noreturn do_exit(long code) */ flush_ptrace_hw_breakpoint(tsk); - TASKS_RCU(preempt_disable()); - TASKS_RCU(tasks_rcu_i = __srcu_read_lock(&tasks_rcu_exit_srcu)); - TASKS_RCU(preempt_enable()); + exit_tasks_rcu_start(); exit_notify(tsk, group_dead); proc_exit_connector(tsk); mpol_put_task_policy(tsk); @@ -918,7 +915,7 @@ void __noreturn do_exit(long code) if (tsk->nr_dirtied) __this_cpu_add(dirty_throttle_leaks, tsk->nr_dirtied); exit_rcu(); - TASKS_RCU(__srcu_read_unlock(&tasks_rcu_exit_srcu, tasks_rcu_i)); + exit_tasks_rcu_finish(); do_task_dead(); } diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 00e77c470017..5033b66d2753 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -568,7 +568,7 @@ static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq); static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock); /* Track exiting tasks in order to allow them to be waited for. */ -DEFINE_SRCU(tasks_rcu_exit_srcu); +DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu); /* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */ #define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10) @@ -875,6 +875,22 @@ static void rcu_spawn_tasks_kthread(void) mutex_unlock(&rcu_tasks_kthread_mutex); } +/* Do the srcu_read_lock() for the above synchronize_srcu(). */ +void exit_tasks_rcu_start(void) +{ + preempt_disable(); + current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu); + preempt_enable(); +} + +/* Do the srcu_read_unlock() for the above synchronize_srcu(). */ +void exit_tasks_rcu_finish(void) +{ + preempt_disable(); + __srcu_read_unlock(&tasks_rcu_exit_srcu, current->rcu_tasks_idx); + preempt_enable(); +} + #endif /* #ifdef CONFIG_TASKS_RCU */ #ifndef CONFIG_TINY_RCU -- cgit v1.2.3 From 352eee1242ef62e18a475ef9278697dbd865969b Mon Sep 17 00:00:00 2001 From: "Luis R. Rodriguez" Date: Tue, 20 Jun 2017 14:45:46 -0700 Subject: swait: Add idle variants which don't contribute to load average There are cases where folks are using an interruptible swait when using kthreads. This is rather confusing given you'd expect interruptible waits to be -- interruptible, but kthreads are not interruptible ! The reason for such practice though is to avoid having these kthreads contribute to the system load average. When systems are idle some kthreads may spend a lot of time blocking if using swait_event_timeout(). This would contribute to the system load average. On systems without preemption this would mean the load average of an idle system is bumped to 2 instead of 0. On systems with PREEMPT=y this would mean the load average of an idle system is bumped to 3 instead of 0. This adds proper API using TASK_IDLE to make such goals explicit and avoid confusion. Suggested-by: "Eric W. Biederman" Acked-by: "Eric W. Biederman" Tested-by: Paul E. McKenney Signed-off-by: Luis R. Rodriguez Signed-off-by: Paul E. McKenney --- include/linux/swait.h | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) (limited to 'include') diff --git a/include/linux/swait.h b/include/linux/swait.h index c1f9c62a8a50..4a4e180d0a35 100644 --- a/include/linux/swait.h +++ b/include/linux/swait.h @@ -169,4 +169,59 @@ do { \ __ret; \ }) +#define __swait_event_idle(wq, condition) \ + (void)___swait_event(wq, condition, TASK_IDLE, 0, schedule()) + +/** + * swait_event_idle - wait without system load contribution + * @wq: the waitqueue to wait on + * @condition: a C expression for the event to wait for + * + * The process is put to sleep (TASK_IDLE) until the @condition evaluates to + * true. The @condition is checked each time the waitqueue @wq is woken up. + * + * This function is mostly used when a kthread or workqueue waits for some + * condition and doesn't want to contribute to system load. Signals are + * ignored. + */ +#define swait_event_idle(wq, condition) \ +do { \ + if (condition) \ + break; \ + __swait_event_idle(wq, condition); \ +} while (0) + +#define __swait_event_idle_timeout(wq, condition, timeout) \ + ___swait_event(wq, ___wait_cond_timeout(condition), \ + TASK_IDLE, timeout, \ + __ret = schedule_timeout(__ret)) + +/** + * swait_event_idle_timeout - wait up to timeout without load contribution + * @wq: the waitqueue to wait on + * @condition: a C expression for the event to wait for + * @timeout: timeout at which we'll give up in jiffies + * + * The process is put to sleep (TASK_IDLE) until the @condition evaluates to + * true. The @condition is checked each time the waitqueue @wq is woken up. + * + * This function is mostly used when a kthread or workqueue waits for some + * condition and doesn't want to contribute to system load. Signals are + * ignored. + * + * Returns: + * 0 if the @condition evaluated to %false after the @timeout elapsed, + * 1 if the @condition evaluated to %true after the @timeout elapsed, + * or the remaining jiffies (at least 1) if the @condition evaluated + * to %true before the @timeout elapsed. + */ +#define swait_event_idle_timeout(wq, condition, timeout) \ +({ \ + long __ret = timeout; \ + if (!___wait_cond_timeout(condition)) \ + __ret = __swait_event_idle_timeout(wq, \ + condition, timeout); \ + __ret; \ +}) + #endif /* _LINUX_SWAIT_H */ -- cgit v1.2.3 From 22e4ebb975822833b083533035233d128b30e98f Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Fri, 28 Jul 2017 16:40:40 -0400 Subject: membarrier: Provide expedited private command Implement MEMBARRIER_CMD_PRIVATE_EXPEDITED with IPIs using cpumask built from all runqueues for which current thread's mm is the same as the thread calling sys_membarrier. It executes faster than the non-expedited variant (no blocking). It also works on NOHZ_FULL configurations. Scheduler-wise, it requires a memory barrier before and after context switching between processes (which have different mm). The memory barrier before context switch is already present. For the barrier after context switch: * Our TSO archs can do RELEASE without being a full barrier. Look at x86 spin_unlock() being a regular STORE for example. But for those archs, all atomics imply smp_mb and all of them have atomic ops in switch_mm() for mm_cpumask(), and on x86 the CR3 load acts as a full barrier. * From all weakly ordered machines, only ARM64 and PPC can do RELEASE, the rest does indeed do smp_mb(), so there the spin_unlock() is a full barrier and we're good. * ARM64 has a very heavy barrier in switch_to(), which suffices. * PPC just removed its barrier from switch_to(), but appears to be talking about adding something to switch_mm(). So add a smp_mb__after_unlock_lock() for now, until this is settled on the PPC side. Changes since v3: - Properly document the memory barriers provided by each architecture. Changes since v2: - Address comments from Peter Zijlstra, - Add smp_mb__after_unlock_lock() after finish_lock_switch() in finish_task_switch() to add the memory barrier we need after storing to rq->curr. This is much simpler than the previous approach relying on atomic_dec_and_test() in mmdrop(), which actually added a memory barrier in the common case of switching between userspace processes. - Return -EINVAL when MEMBARRIER_CMD_SHARED is used on a nohz_full kernel, rather than having the whole membarrier system call returning -ENOSYS. Indeed, CMD_PRIVATE_EXPEDITED is compatible with nohz_full. Adapt the CMD_QUERY mask accordingly. Changes since v1: - move membarrier code under kernel/sched/ because it uses the scheduler runqueue, - only add the barrier when we switch from a kernel thread. The case where we switch from a user-space thread is already handled by the atomic_dec_and_test() in mmdrop(). - add a comment to mmdrop() documenting the requirement on the implicit memory barrier. CC: Peter Zijlstra CC: Paul E. McKenney CC: Boqun Feng CC: Andrew Hunter CC: Maged Michael CC: gromer@google.com CC: Avi Kivity CC: Benjamin Herrenschmidt CC: Paul Mackerras CC: Michael Ellerman Signed-off-by: Mathieu Desnoyers Signed-off-by: Paul E. McKenney Tested-by: Dave Watson --- MAINTAINERS | 2 +- arch/arm64/kernel/process.c | 2 + include/uapi/linux/membarrier.h | 23 +++++- kernel/Makefile | 1 - kernel/membarrier.c | 70 ------------------ kernel/sched/Makefile | 1 + kernel/sched/core.c | 25 +++++++ kernel/sched/membarrier.c | 152 ++++++++++++++++++++++++++++++++++++++++ 8 files changed, 202 insertions(+), 74 deletions(-) delete mode 100644 kernel/membarrier.c create mode 100644 kernel/sched/membarrier.c (limited to 'include') diff --git a/MAINTAINERS b/MAINTAINERS index f66488dfdbc9..3b035584272f 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -8621,7 +8621,7 @@ M: Mathieu Desnoyers M: "Paul E. McKenney" L: linux-kernel@vger.kernel.org S: Supported -F: kernel/membarrier.c +F: kernel/sched/membarrier.c F: include/uapi/linux/membarrier.h MEMORY MANAGEMENT diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 659ae8094ed5..c8f7d98d8cb9 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -360,6 +360,8 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev, /* * Complete any pending TLB or cache maintenance on this CPU in case * the thread migrates to a different CPU. + * This full barrier is also required by the membarrier system + * call. */ dsb(ish); diff --git a/include/uapi/linux/membarrier.h b/include/uapi/linux/membarrier.h index e0b108bd2624..6d47b3249d8a 100644 --- a/include/uapi/linux/membarrier.h +++ b/include/uapi/linux/membarrier.h @@ -40,14 +40,33 @@ * (non-running threads are de facto in such a * state). This covers threads from all processes * running on the system. This command returns 0. + * @MEMBARRIER_CMD_PRIVATE_EXPEDITED: + * Execute a memory barrier on each running + * thread belonging to the same process as the current + * thread. Upon return from system call, the + * caller thread is ensured that all its running + * threads siblings have passed through a state + * where all memory accesses to user-space + * addresses match program order between entry + * to and return from the system call + * (non-running threads are de facto in such a + * state). This only covers threads from the + * same processes as the caller thread. This + * command returns 0. The "expedited" commands + * complete faster than the non-expedited ones, + * they never block, but have the downside of + * causing extra overhead. * * Command to be passed to the membarrier system call. The commands need to * be a single bit each, except for MEMBARRIER_CMD_QUERY which is assigned to * the value 0. */ enum membarrier_cmd { - MEMBARRIER_CMD_QUERY = 0, - MEMBARRIER_CMD_SHARED = (1 << 0), + MEMBARRIER_CMD_QUERY = 0, + MEMBARRIER_CMD_SHARED = (1 << 0), + /* reserved for MEMBARRIER_CMD_SHARED_EXPEDITED (1 << 1) */ + /* reserved for MEMBARRIER_CMD_PRIVATE (1 << 2) */ + MEMBARRIER_CMD_PRIVATE_EXPEDITED = (1 << 3), }; #endif /* _UAPI_LINUX_MEMBARRIER_H */ diff --git a/kernel/Makefile b/kernel/Makefile index 4cb8e8b23c6e..9c323a6daa46 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -108,7 +108,6 @@ obj-$(CONFIG_CRASH_DUMP) += crash_dump.o obj-$(CONFIG_JUMP_LABEL) += jump_label.o obj-$(CONFIG_CONTEXT_TRACKING) += context_tracking.o obj-$(CONFIG_TORTURE_TEST) += torture.o -obj-$(CONFIG_MEMBARRIER) += membarrier.o obj-$(CONFIG_HAS_IOMEM) += memremap.o diff --git a/kernel/membarrier.c b/kernel/membarrier.c deleted file mode 100644 index 9f9284f37f8d..000000000000 --- a/kernel/membarrier.c +++ /dev/null @@ -1,70 +0,0 @@ -/* - * Copyright (C) 2010, 2015 Mathieu Desnoyers - * - * membarrier system call - * - * 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. - */ - -#include -#include -#include - -/* - * Bitmask made from a "or" of all commands within enum membarrier_cmd, - * except MEMBARRIER_CMD_QUERY. - */ -#define MEMBARRIER_CMD_BITMASK (MEMBARRIER_CMD_SHARED) - -/** - * sys_membarrier - issue memory barriers on a set of threads - * @cmd: Takes command values defined in enum membarrier_cmd. - * @flags: Currently needs to be 0. For future extensions. - * - * If this system call is not implemented, -ENOSYS is returned. If the - * command specified does not exist, or if the command argument is invalid, - * this system call returns -EINVAL. For a given command, with flags argument - * set to 0, this system call is guaranteed to always return the same value - * until reboot. - * - * All memory accesses performed in program order from each targeted thread - * is guaranteed to be ordered with respect to sys_membarrier(). If we use - * the semantic "barrier()" to represent a compiler barrier forcing memory - * accesses to be performed in program order across the barrier, and - * smp_mb() to represent explicit memory barriers forcing full memory - * ordering across the barrier, we have the following ordering table for - * each pair of barrier(), sys_membarrier() and smp_mb(): - * - * The pair ordering is detailed as (O: ordered, X: not ordered): - * - * barrier() smp_mb() sys_membarrier() - * barrier() X X O - * smp_mb() X O O - * sys_membarrier() O O O - */ -SYSCALL_DEFINE2(membarrier, int, cmd, int, flags) -{ - /* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */ - if (tick_nohz_full_enabled()) - return -ENOSYS; - if (unlikely(flags)) - return -EINVAL; - switch (cmd) { - case MEMBARRIER_CMD_QUERY: - return MEMBARRIER_CMD_BITMASK; - case MEMBARRIER_CMD_SHARED: - if (num_online_cpus() > 1) - synchronize_sched(); - return 0; - default: - return -EINVAL; - } -} diff --git a/kernel/sched/Makefile b/kernel/sched/Makefile index 53f0164ed362..78f54932ea1d 100644 --- a/kernel/sched/Makefile +++ b/kernel/sched/Makefile @@ -25,3 +25,4 @@ obj-$(CONFIG_SCHED_DEBUG) += debug.o obj-$(CONFIG_CGROUP_CPUACCT) += cpuacct.o obj-$(CONFIG_CPU_FREQ) += cpufreq.o obj-$(CONFIG_CPU_FREQ_GOV_SCHEDUTIL) += cpufreq_schedutil.o +obj-$(CONFIG_MEMBARRIER) += membarrier.o diff --git a/kernel/sched/core.c b/kernel/sched/core.c index bfee6ea7db49..f77269c6c2f8 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2640,6 +2640,16 @@ static struct rq *finish_task_switch(struct task_struct *prev) prev_state = prev->state; vtime_task_switch(prev); perf_event_task_sched_in(prev, current); + /* + * The membarrier system call requires a full memory barrier + * after storing to rq->curr, before going back to user-space. + * + * TODO: This smp_mb__after_unlock_lock can go away if PPC end + * up adding a full barrier to switch_mm(), or we should figure + * out if a smp_mb__after_unlock_lock is really the proper API + * to use. + */ + smp_mb__after_unlock_lock(); finish_lock_switch(rq, prev); finish_arch_post_lock_switch(); @@ -3329,6 +3339,21 @@ static void __sched notrace __schedule(bool preempt) if (likely(prev != next)) { rq->nr_switches++; rq->curr = next; + /* + * The membarrier system call requires each architecture + * to have a full memory barrier after updating + * rq->curr, before returning to user-space. For TSO + * (e.g. x86), the architecture must provide its own + * barrier in switch_mm(). For weakly ordered machines + * for which spin_unlock() acts as a full memory + * barrier, finish_lock_switch() in common code takes + * care of this barrier. For weakly ordered machines for + * which spin_unlock() acts as a RELEASE barrier (only + * arm64 and PowerPC), arm64 has a full barrier in + * switch_to(), and PowerPC has + * smp_mb__after_unlock_lock() before + * finish_lock_switch(). + */ ++*switch_count; trace_sched_switch(preempt, prev, next); diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c new file mode 100644 index 000000000000..a92fddc22747 --- /dev/null +++ b/kernel/sched/membarrier.c @@ -0,0 +1,152 @@ +/* + * Copyright (C) 2010-2017 Mathieu Desnoyers + * + * membarrier system call + * + * 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. + */ + +#include +#include +#include +#include + +#include "sched.h" /* for cpu_rq(). */ + +/* + * Bitmask made from a "or" of all commands within enum membarrier_cmd, + * except MEMBARRIER_CMD_QUERY. + */ +#define MEMBARRIER_CMD_BITMASK \ + (MEMBARRIER_CMD_SHARED | MEMBARRIER_CMD_PRIVATE_EXPEDITED) + +static void ipi_mb(void *info) +{ + smp_mb(); /* IPIs should be serializing but paranoid. */ +} + +static void membarrier_private_expedited(void) +{ + int cpu; + bool fallback = false; + cpumask_var_t tmpmask; + + if (num_online_cpus() == 1) + return; + + /* + * Matches memory barriers around rq->curr modification in + * scheduler. + */ + smp_mb(); /* system call entry is not a mb. */ + + /* + * Expedited membarrier commands guarantee that they won't + * block, hence the GFP_NOWAIT allocation flag and fallback + * implementation. + */ + if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) { + /* Fallback for OOM. */ + fallback = true; + } + + cpus_read_lock(); + for_each_online_cpu(cpu) { + struct task_struct *p; + + /* + * Skipping the current CPU is OK even through we can be + * migrated at any point. The current CPU, at the point + * where we read raw_smp_processor_id(), is ensured to + * be in program order with respect to the caller + * thread. Therefore, we can skip this CPU from the + * iteration. + */ + if (cpu == raw_smp_processor_id()) + continue; + rcu_read_lock(); + p = task_rcu_dereference(&cpu_rq(cpu)->curr); + if (p && p->mm == current->mm) { + if (!fallback) + __cpumask_set_cpu(cpu, tmpmask); + else + smp_call_function_single(cpu, ipi_mb, NULL, 1); + } + rcu_read_unlock(); + } + if (!fallback) { + smp_call_function_many(tmpmask, ipi_mb, NULL, 1); + free_cpumask_var(tmpmask); + } + cpus_read_unlock(); + + /* + * Memory barrier on the caller thread _after_ we finished + * waiting for the last IPI. Matches memory barriers around + * rq->curr modification in scheduler. + */ + smp_mb(); /* exit from system call is not a mb */ +} + +/** + * sys_membarrier - issue memory barriers on a set of threads + * @cmd: Takes command values defined in enum membarrier_cmd. + * @flags: Currently needs to be 0. For future extensions. + * + * If this system call is not implemented, -ENOSYS is returned. If the + * command specified does not exist, not available on the running + * kernel, or if the command argument is invalid, this system call + * returns -EINVAL. For a given command, with flags argument set to 0, + * this system call is guaranteed to always return the same value until + * reboot. + * + * All memory accesses performed in program order from each targeted thread + * is guaranteed to be ordered with respect to sys_membarrier(). If we use + * the semantic "barrier()" to represent a compiler barrier forcing memory + * accesses to be performed in program order across the barrier, and + * smp_mb() to represent explicit memory barriers forcing full memory + * ordering across the barrier, we have the following ordering table for + * each pair of barrier(), sys_membarrier() and smp_mb(): + * + * The pair ordering is detailed as (O: ordered, X: not ordered): + * + * barrier() smp_mb() sys_membarrier() + * barrier() X X O + * smp_mb() X O O + * sys_membarrier() O O O + */ +SYSCALL_DEFINE2(membarrier, int, cmd, int, flags) +{ + if (unlikely(flags)) + return -EINVAL; + switch (cmd) { + case MEMBARRIER_CMD_QUERY: + { + int cmd_mask = MEMBARRIER_CMD_BITMASK; + + if (tick_nohz_full_enabled()) + cmd_mask &= ~MEMBARRIER_CMD_SHARED; + return cmd_mask; + } + case MEMBARRIER_CMD_SHARED: + /* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */ + if (tick_nohz_full_enabled()) + return -EINVAL; + if (num_online_cpus() > 1) + synchronize_sched(); + return 0; + case MEMBARRIER_CMD_PRIVATE_EXPEDITED: + membarrier_private_expedited(); + return 0; + default: + return -EINVAL; + } +} -- cgit v1.2.3 From d3a024abbc438277851c510b51ec9b158821488b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 29 Jun 2017 15:47:44 -0700 Subject: locking: Remove spin_unlock_wait() generic definitions There is no agreed-upon definition of spin_unlock_wait()'s semantics, and it appears that all callers could do just as well with a lock/unlock pair. This commit therefore removes spin_unlock_wait() and related definitions from core code. Signed-off-by: Paul E. McKenney Cc: Arnd Bergmann Cc: Ingo Molnar Cc: Will Deacon Cc: Peter Zijlstra Cc: Alan Stern Cc: Andrea Parri Cc: Linus Torvalds --- include/asm-generic/qspinlock.h | 14 ----- include/linux/spinlock.h | 11 ---- include/linux/spinlock_up.h | 6 --- kernel/locking/qspinlock.c | 117 ---------------------------------------- 4 files changed, 148 deletions(-) (limited to 'include') diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h index 9f0681bf1e87..66260777d644 100644 --- a/include/asm-generic/qspinlock.h +++ b/include/asm-generic/qspinlock.h @@ -21,17 +21,6 @@ #include -/** - * queued_spin_unlock_wait - wait until the _current_ lock holder releases the lock - * @lock : Pointer to queued spinlock structure - * - * There is a very slight possibility of live-lock if the lockers keep coming - * and the waiter is just unfortunate enough to not see any unlock state. - */ -#ifndef queued_spin_unlock_wait -extern void queued_spin_unlock_wait(struct qspinlock *lock); -#endif - /** * queued_spin_is_locked - is the spinlock locked? * @lock: Pointer to queued spinlock structure @@ -41,8 +30,6 @@ extern void queued_spin_unlock_wait(struct qspinlock *lock); static __always_inline int queued_spin_is_locked(struct qspinlock *lock) { /* - * See queued_spin_unlock_wait(). - * * Any !0 state indicates it is locked, even if _Q_LOCKED_VAL * isn't immediately observable. */ @@ -135,6 +122,5 @@ static __always_inline bool virt_spin_lock(struct qspinlock *lock) #define arch_spin_trylock(l) queued_spin_trylock(l) #define arch_spin_unlock(l) queued_spin_unlock(l) #define arch_spin_lock_flags(l, f) queued_spin_lock(l) -#define arch_spin_unlock_wait(l) queued_spin_unlock_wait(l) #endif /* __ASM_GENERIC_QSPINLOCK_H */ diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h index 59248dcc6ef3..ef018a6e4985 100644 --- a/include/linux/spinlock.h +++ b/include/linux/spinlock.h @@ -130,12 +130,6 @@ do { \ #define smp_mb__before_spinlock() smp_wmb() #endif -/** - * raw_spin_unlock_wait - wait until the spinlock gets unlocked - * @lock: the spinlock in question. - */ -#define raw_spin_unlock_wait(lock) arch_spin_unlock_wait(&(lock)->raw_lock) - #ifdef CONFIG_DEBUG_SPINLOCK extern void do_raw_spin_lock(raw_spinlock_t *lock) __acquires(lock); #define do_raw_spin_lock_flags(lock, flags) do_raw_spin_lock(lock) @@ -369,11 +363,6 @@ static __always_inline int spin_trylock_irq(spinlock_t *lock) raw_spin_trylock_irqsave(spinlock_check(lock), flags); \ }) -static __always_inline void spin_unlock_wait(spinlock_t *lock) -{ - raw_spin_unlock_wait(&lock->rlock); -} - static __always_inline int spin_is_locked(spinlock_t *lock) { return raw_spin_is_locked(&lock->rlock); diff --git a/include/linux/spinlock_up.h b/include/linux/spinlock_up.h index 0d9848de677d..612fb530af41 100644 --- a/include/linux/spinlock_up.h +++ b/include/linux/spinlock_up.h @@ -26,11 +26,6 @@ #ifdef CONFIG_DEBUG_SPINLOCK #define arch_spin_is_locked(x) ((x)->slock == 0) -static inline void arch_spin_unlock_wait(arch_spinlock_t *lock) -{ - smp_cond_load_acquire(&lock->slock, VAL); -} - static inline void arch_spin_lock(arch_spinlock_t *lock) { lock->slock = 0; @@ -73,7 +68,6 @@ static inline void arch_spin_unlock(arch_spinlock_t *lock) #else /* DEBUG_SPINLOCK */ #define arch_spin_is_locked(lock) ((void)(lock), 0) -#define arch_spin_unlock_wait(lock) do { barrier(); (void)(lock); } while (0) /* for sched/core.c and kernel_lock.c: */ # define arch_spin_lock(lock) do { barrier(); (void)(lock); } while (0) # define arch_spin_lock_flags(lock, flags) do { barrier(); (void)(lock); } while (0) diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index fd24153e8a48..294294c71ba4 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -268,123 +268,6 @@ static __always_inline u32 __pv_wait_head_or_lock(struct qspinlock *lock, #define queued_spin_lock_slowpath native_queued_spin_lock_slowpath #endif -/* - * Various notes on spin_is_locked() and spin_unlock_wait(), which are - * 'interesting' functions: - * - * PROBLEM: some architectures have an interesting issue with atomic ACQUIRE - * operations in that the ACQUIRE applies to the LOAD _not_ the STORE (ARM64, - * PPC). Also qspinlock has a similar issue per construction, the setting of - * the locked byte can be unordered acquiring the lock proper. - * - * This gets to be 'interesting' in the following cases, where the /should/s - * end up false because of this issue. - * - * - * CASE 1: - * - * So the spin_is_locked() correctness issue comes from something like: - * - * CPU0 CPU1 - * - * global_lock(); local_lock(i) - * spin_lock(&G) spin_lock(&L[i]) - * for (i) if (!spin_is_locked(&G)) { - * spin_unlock_wait(&L[i]); smp_acquire__after_ctrl_dep(); - * return; - * } - * // deal with fail - * - * Where it is important CPU1 sees G locked or CPU0 sees L[i] locked such - * that there is exclusion between the two critical sections. - * - * The load from spin_is_locked(&G) /should/ be constrained by the ACQUIRE from - * spin_lock(&L[i]), and similarly the load(s) from spin_unlock_wait(&L[i]) - * /should/ be constrained by the ACQUIRE from spin_lock(&G). - * - * Similarly, later stuff is constrained by the ACQUIRE from CTRL+RMB. - * - * - * CASE 2: - * - * For spin_unlock_wait() there is a second correctness issue, namely: - * - * CPU0 CPU1 - * - * flag = set; - * smp_mb(); spin_lock(&l) - * spin_unlock_wait(&l); if (!flag) - * // add to lockless list - * spin_unlock(&l); - * // iterate lockless list - * - * Which wants to ensure that CPU1 will stop adding bits to the list and CPU0 - * will observe the last entry on the list (if spin_unlock_wait() had ACQUIRE - * semantics etc..) - * - * Where flag /should/ be ordered against the locked store of l. - */ - -/* - * queued_spin_lock_slowpath() can (load-)ACQUIRE the lock before - * issuing an _unordered_ store to set _Q_LOCKED_VAL. - * - * This means that the store can be delayed, but no later than the - * store-release from the unlock. This means that simply observing - * _Q_LOCKED_VAL is not sufficient to determine if the lock is acquired. - * - * There are two paths that can issue the unordered store: - * - * (1) clear_pending_set_locked(): *,1,0 -> *,0,1 - * - * (2) set_locked(): t,0,0 -> t,0,1 ; t != 0 - * atomic_cmpxchg_relaxed(): t,0,0 -> 0,0,1 - * - * However, in both cases we have other !0 state we've set before to queue - * ourseves: - * - * For (1) we have the atomic_cmpxchg_acquire() that set _Q_PENDING_VAL, our - * load is constrained by that ACQUIRE to not pass before that, and thus must - * observe the store. - * - * For (2) we have a more intersting scenario. We enqueue ourselves using - * xchg_tail(), which ends up being a RELEASE. This in itself is not - * sufficient, however that is followed by an smp_cond_acquire() on the same - * word, giving a RELEASE->ACQUIRE ordering. This again constrains our load and - * guarantees we must observe that store. - * - * Therefore both cases have other !0 state that is observable before the - * unordered locked byte store comes through. This means we can use that to - * wait for the lock store, and then wait for an unlock. - */ -#ifndef queued_spin_unlock_wait -void queued_spin_unlock_wait(struct qspinlock *lock) -{ - u32 val; - - for (;;) { - val = atomic_read(&lock->val); - - if (!val) /* not locked, we're done */ - goto done; - - if (val & _Q_LOCKED_MASK) /* locked, go wait for unlock */ - break; - - /* not locked, but pending, wait until we observe the lock */ - cpu_relax(); - } - - /* any unlock is good */ - while (atomic_read(&lock->val) & _Q_LOCKED_MASK) - cpu_relax(); - -done: - smp_acquire__after_ctrl_dep(); -} -EXPORT_SYMBOL(queued_spin_unlock_wait); -#endif - #endif /* _GEN_PV_LOCK_SLOWPATH */ /** -- cgit v1.2.3