/* * Read-Copy Update mechanism for mutual exclusion * * 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, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. * * Copyright IBM Corporation, 2001 * * Authors: Dipankar Sarma <dipankar@in.ibm.com> * Manfred Spraul <manfred@colorfullife.com> * * Based on the original work by Paul McKenney <paulmck@us.ibm.com> * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. * Papers: * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) * * For detailed explanation of Read-Copy Update mechanism see - * http://lse.sourceforge.net/locking/rcupdate.html * */ #include <linux/types.h> #include <linux/kernel.h> #include <linux/init.h> #include <linux/spinlock.h> #include <linux/smp.h> #include <linux/interrupt.h> #include <linux/sched.h> #include <linux/atomic.h> #include <linux/bitops.h> #include <linux/percpu.h> #include <linux/notifier.h> #include <linux/cpu.h> #include <linux/mutex.h> #include <linux/export.h> #include <linux/hardirq.h> #include <linux/delay.h> #include <linux/module.h> #define CREATE_TRACE_POINTS #include <trace/events/rcu.h> #include "rcu.h" module_param(rcu_expedited, int, 0); #ifdef CONFIG_PREEMPT_RCU /* * Preemptible RCU implementation for rcu_read_lock(). * Just increment ->rcu_read_lock_nesting, shared state will be updated * if we block. */ void __rcu_read_lock(void) { current->rcu_read_lock_nesting++; barrier(); /* critical section after entry code. */ } EXPORT_SYMBOL_GPL(__rcu_read_lock); /* * Preemptible RCU implementation for rcu_read_unlock(). * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then * invoke rcu_read_unlock_special() to clean up after a context switch * in an RCU read-side critical section and other special cases. */ void __rcu_read_unlock(void) { struct task_struct *t = current; if (t->rcu_read_lock_nesting != 1) { --t->rcu_read_lock_nesting; } else { barrier(); /* critical section before exit code. */ t->rcu_read_lock_nesting = INT_MIN; #ifdef CONFIG_PROVE_RCU_DELAY udelay(10); /* Make preemption more probable. */ #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */ barrier(); /* assign before ->rcu_read_unlock_special load */ if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) rcu_read_unlock_special(t); barrier(); /* ->rcu_read_unlock_special load before assign */ t->rcu_read_lock_nesting = 0; } #ifdef CONFIG_PROVE_LOCKING { int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting); WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); } #endif /* #ifdef CONFIG_PROVE_LOCKING */ } EXPORT_SYMBOL_GPL(__rcu_read_unlock); /* * Check for a task exiting while in a preemptible-RCU read-side * critical section, clean up if so. No need to issue warnings, * as debug_check_no_locks_held() already does this if lockdep * is enabled. */ void exit_rcu(void) { struct task_struct *t = current; if (likely(list_empty(¤t->rcu_node_entry))) return; t->rcu_read_lock_nesting = 1; barrier(); t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED; __rcu_read_unlock(); } #else /* #ifdef CONFIG_PREEMPT_RCU */ void exit_rcu(void) { } #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ #ifdef CONFIG_DEBUG_LOCK_ALLOC static struct lock_class_key rcu_lock_key; struct lockdep_map rcu_lock_map = STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key); EXPORT_SYMBOL_GPL(rcu_lock_map); static struct lock_class_key rcu_bh_lock_key; struct lockdep_map rcu_bh_lock_map = STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key); EXPORT_SYMBOL_GPL(rcu_bh_lock_map); static struct lock_class_key rcu_sched_lock_key; struct lockdep_map rcu_sched_lock_map = STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key); EXPORT_SYMBOL_GPL(rcu_sched_lock_map); #endif #ifdef CONFIG_DEBUG_LOCK_ALLOC int debug_lockdep_rcu_enabled(void) { return rcu_scheduler_active && debug_locks && current->lockdep_recursion == 0; } EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); /** * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section? * * Check for bottom half being disabled, which covers both the * CONFIG_PROVE_RCU and not cases. Note that if someone uses * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled) * will show the situation. This is useful for debug checks in functions * that require that they be called within an RCU read-side critical * section. * * Check debug_lockdep_rcu_enabled() to prevent false positives during boot. * * Note that rcu_read_lock() is disallowed if the CPU is either idle or * offline from an RCU perspective, so check for those as well. */ int rcu_read_lock_bh_held(void) { if (!debug_lockdep_rcu_enabled()) return 1; if (rcu_is_cpu_idle()) return 0; if (!rcu_lockdep_current_cpu_online()) return 0; return in_softirq() || irqs_disabled(); } EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ struct rcu_synchronize { struct rcu_head head; struct completion completion; }; /* * Awaken the corresponding synchronize_rcu() instance now that a * grace period has elapsed. */ static void wakeme_after_rcu(struct rcu_head *head) { struct rcu_synchronize *rcu; rcu = container_of(head, struct rcu_synchronize, head); complete(&rcu->completion); } void wait_rcu_gp(call_rcu_func_t crf) { struct rcu_synchronize rcu; init_rcu_head_on_stack(&rcu.head); init_completion(&rcu.completion); /* Will wake me after RCU finished. */ crf(&rcu.head, wakeme_after_rcu); /* Wait for it. */ wait_for_completion(&rcu.completion); destroy_rcu_head_on_stack(&rcu.head); } EXPORT_SYMBOL_GPL(wait_rcu_gp); #ifdef CONFIG_PROVE_RCU /* * wrapper function to avoid #include problems. */ int rcu_my_thread_group_empty(void) { return thread_group_empty(current); } EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty); #endif /* #ifdef CONFIG_PROVE_RCU */ #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD static inline void debug_init_rcu_head(struct rcu_head *head) { debug_object_init(head, &rcuhead_debug_descr); } static inline void debug_rcu_head_free(struct rcu_head *head) { debug_object_free(head, &rcuhead_debug_descr); } /* * fixup_init is called when: * - an active object is initialized */ static int rcuhead_fixup_init(void *addr, enum debug_obj_state state) { struct rcu_head *head = addr; switch (state) { case ODEBUG_STATE_ACTIVE: /* * Ensure that queued callbacks are all executed. * If we detect that we are nested in a RCU read-side critical * section, we should simply fail, otherwise we would deadlock. * In !PREEMPT configurations, there is no way to tell if we are * in a RCU read-side critical section or not, so we never * attempt any fixup and just print a warning. */ #ifndef CONFIG_PREEMPT WARN_ON_ONCE(1); return 0; #endif if (rcu_preempt_depth() != 0 || preempt_count() != 0 || irqs_disabled()) { WARN_ON_ONCE(1); return 0; } rcu_barrier(); rcu_barrier_sched(); rcu_barrier_bh(); debug_object_init(head, &rcuhead_debug_descr); return 1; default: return 0; } } /* * fixup_activate is called when: * - an active object is activated * - an unknown object is activated (might be a statically initialized object) * Activation is performed internally by call_rcu(). */ static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state) { struct rcu_head *head = addr; switch (state) { case ODEBUG_STATE_NOTAVAILABLE: /* * This is not really a fixup. We just make sure that it is * tracked in the object tracker. */ debug_object_init(head, &rcuhead_debug_descr); debug_object_activate(head, &rcuhead_debug_descr); return 0; case ODEBUG_STATE_ACTIVE: /* * Ensure that queued callbacks are all executed. * If we detect that we are nested in a RCU read-side critical * section, we should simply fail, otherwise we would deadlock. * In !PREEMPT configurations, there is no way to tell if we are * in a RCU read-side critical section or not, so we never * attempt any fixup and just print a warning. */ #ifndef CONFIG_PREEMPT WARN_ON_ONCE(1); return 0; #endif if (rcu_preempt_depth() != 0 || preempt_count() != 0 || irqs_disabled()) { WARN_ON_ONCE(1); return 0; } rcu_barrier(); rcu_barrier_sched(); rcu_barrier_bh(); debug_object_activate(head, &rcuhead_debug_descr); return 1; default: return 0; } } /* * fixup_free is called when: * - an active object is freed */ static int rcuhead_fixup_free(void *addr, enum debug_obj_state state) { struct rcu_head *head = addr; switch (state) { case ODEBUG_STATE_ACTIVE: /* * Ensure that queued callbacks are all executed. * If we detect that we are nested in a RCU read-side critical * section, we should simply fail, otherwise we would deadlock. * In !PREEMPT configurations, there is no way to tell if we are * in a RCU read-side critical section or not, so we never * attempt any fixup and just print a warning. */ #ifndef CONFIG_PREEMPT WARN_ON_ONCE(1); return 0; #endif if (rcu_preempt_depth() != 0 || preempt_count() != 0 || irqs_disabled()) { WARN_ON_ONCE(1); return 0; } rcu_barrier(); rcu_barrier_sched(); rcu_barrier_bh(); debug_object_free(head, &rcuhead_debug_descr); return 1; default: return 0; } } /** * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects * @head: pointer to rcu_head structure to be initialized * * This function informs debugobjects of a new rcu_head structure that * has been allocated as an auto variable on the stack. This function * is not required for rcu_head structures that are statically defined or * that are dynamically allocated on the heap. This function has no * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. */ void init_rcu_head_on_stack(struct rcu_head *head) { debug_object_init_on_stack(head, &rcuhead_debug_descr); } EXPORT_SYMBOL_GPL(init_rcu_head_on_stack); /** * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects * @head: pointer to rcu_head structure to be initialized * * This function informs debugobjects that an on-stack rcu_head structure * is about to go out of scope. As with init_rcu_head_on_stack(), this * function is not required for rcu_head structures that are statically * defined or that are dynamically allocated on the heap. Also as with * init_rcu_head_on_stack(), this function has no effect for * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. */ void destroy_rcu_head_on_stack(struct rcu_head *head) { debug_object_free(head, &rcuhead_debug_descr); } EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack); struct debug_obj_descr rcuhead_debug_descr = { .name = "rcu_head", .fixup_init = rcuhead_fixup_init, .fixup_activate = rcuhead_fixup_activate, .fixup_free = rcuhead_fixup_free, }; EXPORT_SYMBOL_GPL(rcuhead_debug_descr); #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE) void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp, unsigned long secs, unsigned long c_old, unsigned long c) { trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c); } EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read); #else #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \ do { } while (0) #endif #ifdef CONFIG_RCU_STALL_COMMON #ifdef CONFIG_PROVE_RCU #define RCU_STALL_DELAY_DELTA (5 * HZ) #else #define RCU_STALL_DELAY_DELTA 0 #endif int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */ int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; module_param(rcu_cpu_stall_suppress, int, 0644); module_param(rcu_cpu_stall_timeout, int, 0644); int rcu_jiffies_till_stall_check(void) { int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout); /* * Limit check must be consistent with the Kconfig limits * for CONFIG_RCU_CPU_STALL_TIMEOUT. */ if (till_stall_check < 3) { ACCESS_ONCE(rcu_cpu_stall_timeout) = 3; till_stall_check = 3; } else if (till_stall_check > 300) { ACCESS_ONCE(rcu_cpu_stall_timeout) = 300; till_stall_check = 300; } return till_stall_check * HZ + RCU_STALL_DELAY_DELTA; } static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr) { rcu_cpu_stall_suppress = 1; return NOTIFY_DONE; } static struct notifier_block rcu_panic_block = { .notifier_call = rcu_panic, }; static int __init check_cpu_stall_init(void) { atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block); return 0; } early_initcall(check_cpu_stall_init); #endif /* #ifdef CONFIG_RCU_STALL_COMMON */