1 /* SPDX-License-Identifier: GPL-2.0+ */ 2 /* 3 * Read-Copy Update mechanism for mutual exclusion, adapted for tracing. 4 * 5 * Copyright (C) 2020 Paul E. McKenney. 6 */ 7 8 #ifndef __LINUX_RCUPDATE_TRACE_H 9 #define __LINUX_RCUPDATE_TRACE_H 10 11 #include <linux/sched.h> 12 #include <linux/rcupdate.h> 13 14 extern struct lockdep_map rcu_trace_lock_map; 15 16 #ifdef CONFIG_DEBUG_LOCK_ALLOC 17 18 static inline int rcu_read_lock_trace_held(void) 19 { 20 return lock_is_held(&rcu_trace_lock_map); 21 } 22 23 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 24 25 static inline int rcu_read_lock_trace_held(void) 26 { 27 return 1; 28 } 29 30 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 31 32 #ifdef CONFIG_TASKS_TRACE_RCU 33 34 void rcu_read_unlock_trace_special(struct task_struct *t, int nesting); 35 36 /** 37 * rcu_read_lock_trace - mark beginning of RCU-trace read-side critical section 38 * 39 * When synchronize_rcu_tasks_trace() is invoked by one task, then that 40 * task is guaranteed to block until all other tasks exit their read-side 41 * critical sections. Similarly, if call_rcu_trace() is invoked on one 42 * task while other tasks are within RCU read-side critical sections, 43 * invocation of the corresponding RCU callback is deferred until after 44 * the all the other tasks exit their critical sections. 45 * 46 * For more details, please see the documentation for rcu_read_lock(). 47 */ 48 static inline void rcu_read_lock_trace(void) 49 { 50 struct task_struct *t = current; 51 52 WRITE_ONCE(t->trc_reader_nesting, READ_ONCE(t->trc_reader_nesting) + 1); 53 barrier(); 54 if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && 55 t->trc_reader_special.b.need_mb) 56 smp_mb(); // Pairs with update-side barriers 57 rcu_lock_acquire(&rcu_trace_lock_map); 58 } 59 60 /** 61 * rcu_read_unlock_trace - mark end of RCU-trace read-side critical section 62 * 63 * Pairs with a preceding call to rcu_read_lock_trace(), and nesting is 64 * allowed. Invoking a rcu_read_unlock_trace() when there is no matching 65 * rcu_read_lock_trace() is verboten, and will result in lockdep complaints. 66 * 67 * For more details, please see the documentation for rcu_read_unlock(). 68 */ 69 static inline void rcu_read_unlock_trace(void) 70 { 71 int nesting; 72 struct task_struct *t = current; 73 74 rcu_lock_release(&rcu_trace_lock_map); 75 nesting = READ_ONCE(t->trc_reader_nesting) - 1; 76 barrier(); // Critical section before disabling. 77 // Disable IPI-based setting of .need_qs. 78 WRITE_ONCE(t->trc_reader_nesting, INT_MIN); 79 if (likely(!READ_ONCE(t->trc_reader_special.s)) || nesting) { 80 WRITE_ONCE(t->trc_reader_nesting, nesting); 81 return; // We assume shallow reader nesting. 82 } 83 rcu_read_unlock_trace_special(t, nesting); 84 } 85 86 void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func); 87 void synchronize_rcu_tasks_trace(void); 88 void rcu_barrier_tasks_trace(void); 89 #else 90 /* 91 * The BPF JIT forms these addresses even when it doesn't call these 92 * functions, so provide definitions that result in runtime errors. 93 */ 94 static inline void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func) { BUG(); } 95 static inline void rcu_read_lock_trace(void) { BUG(); } 96 static inline void rcu_read_unlock_trace(void) { BUG(); } 97 #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */ 98 99 #endif /* __LINUX_RCUPDATE_TRACE_H */ 100