| 1 | /* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1) |
| 2 | * |
| 3 | * lttng-tracker-pid.c |
| 4 | * |
| 5 | * LTTng Process ID tracking. |
| 6 | * |
| 7 | * Copyright (C) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 8 | */ |
| 9 | |
| 10 | #include <linux/module.h> |
| 11 | #include <linux/slab.h> |
| 12 | #include <linux/err.h> |
| 13 | #include <linux/seq_file.h> |
| 14 | #include <linux/stringify.h> |
| 15 | #include <linux/hash.h> |
| 16 | #include <linux/rcupdate.h> |
| 17 | |
| 18 | #include <wrapper/tracepoint.h> |
| 19 | #include <wrapper/rcu.h> |
| 20 | #include <wrapper/list.h> |
| 21 | #include <lttng-events.h> |
| 22 | |
| 23 | /* |
| 24 | * Hash table is allocated and freed when there are no possible |
| 25 | * concurrent lookups (ensured by the alloc/free caller). However, |
| 26 | * there can be concurrent RCU lookups vs add/del operations. |
| 27 | * |
| 28 | * Concurrent updates of the PID hash table are forbidden: the caller |
| 29 | * must ensure mutual exclusion. This is currently done by holding the |
| 30 | * sessions_mutex across calls to create, destroy, add, and del |
| 31 | * functions of this API. |
| 32 | */ |
| 33 | int lttng_pid_tracker_get_node_pid(const struct lttng_pid_hash_node *node) |
| 34 | { |
| 35 | return node->pid; |
| 36 | } |
| 37 | |
| 38 | /* |
| 39 | * Lookup performed from RCU read-side critical section (RCU sched), |
| 40 | * protected by preemption off at the tracepoint call site. |
| 41 | * Return 1 if found, 0 if not found. |
| 42 | */ |
| 43 | bool lttng_pid_tracker_lookup(struct lttng_pid_tracker *lpf, int pid) |
| 44 | { |
| 45 | struct hlist_head *head; |
| 46 | struct lttng_pid_hash_node *e; |
| 47 | uint32_t hash = hash_32(pid, 32); |
| 48 | |
| 49 | head = &lpf->pid_hash[hash & (LTTNG_PID_TABLE_SIZE - 1)]; |
| 50 | lttng_hlist_for_each_entry_rcu(e, head, hlist) { |
| 51 | if (pid == e->pid) |
| 52 | return 1; /* Found */ |
| 53 | } |
| 54 | return 0; |
| 55 | } |
| 56 | EXPORT_SYMBOL_GPL(lttng_pid_tracker_lookup); |
| 57 | |
| 58 | /* |
| 59 | * Tracker add and del operations support concurrent RCU lookups. |
| 60 | */ |
| 61 | int lttng_pid_tracker_add(struct lttng_pid_tracker *lpf, int pid) |
| 62 | { |
| 63 | struct hlist_head *head; |
| 64 | struct lttng_pid_hash_node *e; |
| 65 | uint32_t hash = hash_32(pid, 32); |
| 66 | |
| 67 | head = &lpf->pid_hash[hash & (LTTNG_PID_TABLE_SIZE - 1)]; |
| 68 | lttng_hlist_for_each_entry(e, head, hlist) { |
| 69 | if (pid == e->pid) |
| 70 | return -EEXIST; |
| 71 | } |
| 72 | e = kmalloc(sizeof(struct lttng_pid_hash_node), GFP_KERNEL); |
| 73 | if (!e) |
| 74 | return -ENOMEM; |
| 75 | e->pid = pid; |
| 76 | hlist_add_head_rcu(&e->hlist, head); |
| 77 | return 0; |
| 78 | } |
| 79 | |
| 80 | static |
| 81 | void pid_tracker_del_node_rcu(struct lttng_pid_hash_node *e) |
| 82 | { |
| 83 | hlist_del_rcu(&e->hlist); |
| 84 | /* |
| 85 | * We choose to use a heavyweight synchronize on removal here, |
| 86 | * since removal of a PID from the tracker mask is a rare |
| 87 | * operation, and we don't want to use more cache lines than |
| 88 | * what we really need when doing the PID lookups, so we don't |
| 89 | * want to afford adding a rcu_head field to those pid hash |
| 90 | * node. |
| 91 | */ |
| 92 | synchronize_trace(); |
| 93 | kfree(e); |
| 94 | } |
| 95 | |
| 96 | /* |
| 97 | * This removal is only used on destroy, so it does not need to support |
| 98 | * concurrent RCU lookups. |
| 99 | */ |
| 100 | static |
| 101 | void pid_tracker_del_node(struct lttng_pid_hash_node *e) |
| 102 | { |
| 103 | hlist_del(&e->hlist); |
| 104 | kfree(e); |
| 105 | } |
| 106 | |
| 107 | int lttng_pid_tracker_del(struct lttng_pid_tracker *lpf, int pid) |
| 108 | { |
| 109 | struct hlist_head *head; |
| 110 | struct lttng_pid_hash_node *e; |
| 111 | uint32_t hash = hash_32(pid, 32); |
| 112 | |
| 113 | head = &lpf->pid_hash[hash & (LTTNG_PID_TABLE_SIZE - 1)]; |
| 114 | /* |
| 115 | * No need of _safe iteration, because we stop traversal as soon |
| 116 | * as we remove the entry. |
| 117 | */ |
| 118 | lttng_hlist_for_each_entry(e, head, hlist) { |
| 119 | if (pid == e->pid) { |
| 120 | pid_tracker_del_node_rcu(e); |
| 121 | return 0; |
| 122 | } |
| 123 | } |
| 124 | return -ENOENT; /* Not found */ |
| 125 | } |
| 126 | |
| 127 | struct lttng_pid_tracker *lttng_pid_tracker_create(void) |
| 128 | { |
| 129 | return kzalloc(sizeof(struct lttng_pid_tracker), GFP_KERNEL); |
| 130 | } |
| 131 | |
| 132 | void lttng_pid_tracker_destroy(struct lttng_pid_tracker *lpf) |
| 133 | { |
| 134 | int i; |
| 135 | |
| 136 | for (i = 0; i < LTTNG_PID_TABLE_SIZE; i++) { |
| 137 | struct hlist_head *head = &lpf->pid_hash[i]; |
| 138 | struct lttng_pid_hash_node *e; |
| 139 | struct hlist_node *tmp; |
| 140 | |
| 141 | lttng_hlist_for_each_entry_safe(e, tmp, head, hlist) |
| 142 | pid_tracker_del_node(e); |
| 143 | } |
| 144 | kfree(lpf); |
| 145 | } |