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
rcu_read_lock_trace_held(void)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
rcu_read_lock_trace_held(void)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);
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 */
rcu_read_lock_trace(void)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 */
rcu_read_unlock_trace(void)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 + nesting);
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 WARN_ON_ONCE(nesting != 0);
84 rcu_read_unlock_trace_special(t);
85 }
86
87 void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);
88 void synchronize_rcu_tasks_trace(void);
89 void rcu_barrier_tasks_trace(void);
90 struct task_struct *get_rcu_tasks_trace_gp_kthread(void);
91 #else
92 /*
93 * The BPF JIT forms these addresses even when it doesn't call these
94 * functions, so provide definitions that result in runtime errors.
95 */
call_rcu_tasks_trace(struct rcu_head * rhp,rcu_callback_t func)96 static inline void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func) { BUG(); }
rcu_read_lock_trace(void)97 static inline void rcu_read_lock_trace(void) { BUG(); }
rcu_read_unlock_trace(void)98 static inline void rcu_read_unlock_trace(void) { BUG(); }
99 #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
100
101 #endif /* __LINUX_RCUPDATE_TRACE_H */
102