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1// SPDX-License-Identifier: GPL-2.0
2#define CREATE_TRACE_POINTS
3#include <trace/events/mmap_lock.h>
4
5#include <linux/mm.h>
6#include <linux/cgroup.h>
7#include <linux/memcontrol.h>
8#include <linux/mmap_lock.h>
9#include <linux/mutex.h>
10#include <linux/percpu.h>
11#include <linux/rcupdate.h>
12#include <linux/smp.h>
13#include <linux/trace_events.h>
14#include <linux/local_lock.h>
15
16EXPORT_TRACEPOINT_SYMBOL(mmap_lock_start_locking);
17EXPORT_TRACEPOINT_SYMBOL(mmap_lock_acquire_returned);
18EXPORT_TRACEPOINT_SYMBOL(mmap_lock_released);
19
20#ifdef CONFIG_MEMCG
21
22/*
23 * Our various events all share the same buffer (because we don't want or need
24 * to allocate a set of buffers *per event type*), so we need to protect against
25 * concurrent _reg() and _unreg() calls, and count how many _reg() calls have
26 * been made.
27 */
28static DEFINE_MUTEX(reg_lock);
29static int reg_refcount; /* Protected by reg_lock. */
30
31/*
32 * Size of the buffer for memcg path names. Ignoring stack trace support,
33 * trace_events_hist.c uses MAX_FILTER_STR_VAL for this, so we also use it.
34 */
35#define MEMCG_PATH_BUF_SIZE MAX_FILTER_STR_VAL
36
37/*
38 * How many contexts our trace events might be called in: normal, softirq, irq,
39 * and NMI.
40 */
41#define CONTEXT_COUNT 4
42
43struct memcg_path {
44 local_lock_t lock;
45 char __rcu *buf;
46 local_t buf_idx;
47};
48static DEFINE_PER_CPU(struct memcg_path, memcg_paths) = {
49 .lock = INIT_LOCAL_LOCK(lock),
50 .buf_idx = LOCAL_INIT(0),
51};
52
53static char **tmp_bufs;
54
55/* Called with reg_lock held. */
56static void free_memcg_path_bufs(void)
57{
58 struct memcg_path *memcg_path;
59 int cpu;
60 char **old = tmp_bufs;
61
62 for_each_possible_cpu(cpu) {
63 memcg_path = per_cpu_ptr(&memcg_paths, cpu);
64 *(old++) = rcu_dereference_protected(memcg_path->buf,
65 lockdep_is_held(®_lock));
66 rcu_assign_pointer(memcg_path->buf, NULL);
67 }
68
69 /* Wait for inflight memcg_path_buf users to finish. */
70 synchronize_rcu();
71
72 old = tmp_bufs;
73 for_each_possible_cpu(cpu) {
74 kfree(*(old++));
75 }
76
77 kfree(tmp_bufs);
78 tmp_bufs = NULL;
79}
80
81int trace_mmap_lock_reg(void)
82{
83 int cpu;
84 char *new;
85
86 mutex_lock(®_lock);
87
88 /* If the refcount is going 0->1, proceed with allocating buffers. */
89 if (reg_refcount++)
90 goto out;
91
92 tmp_bufs = kmalloc_array(num_possible_cpus(), sizeof(*tmp_bufs),
93 GFP_KERNEL);
94 if (tmp_bufs == NULL)
95 goto out_fail;
96
97 for_each_possible_cpu(cpu) {
98 new = kmalloc(MEMCG_PATH_BUF_SIZE * CONTEXT_COUNT, GFP_KERNEL);
99 if (new == NULL)
100 goto out_fail_free;
101 rcu_assign_pointer(per_cpu_ptr(&memcg_paths, cpu)->buf, new);
102 /* Don't need to wait for inflights, they'd have gotten NULL. */
103 }
104
105out:
106 mutex_unlock(®_lock);
107 return 0;
108
109out_fail_free:
110 free_memcg_path_bufs();
111out_fail:
112 /* Since we failed, undo the earlier ref increment. */
113 --reg_refcount;
114
115 mutex_unlock(®_lock);
116 return -ENOMEM;
117}
118
119void trace_mmap_lock_unreg(void)
120{
121 mutex_lock(®_lock);
122
123 /* If the refcount is going 1->0, proceed with freeing buffers. */
124 if (--reg_refcount)
125 goto out;
126
127 free_memcg_path_bufs();
128
129out:
130 mutex_unlock(®_lock);
131}
132
133static inline char *get_memcg_path_buf(void)
134{
135 struct memcg_path *memcg_path = this_cpu_ptr(&memcg_paths);
136 char *buf;
137 int idx;
138
139 rcu_read_lock();
140 buf = rcu_dereference(memcg_path->buf);
141 if (buf == NULL) {
142 rcu_read_unlock();
143 return NULL;
144 }
145 idx = local_add_return(MEMCG_PATH_BUF_SIZE, &memcg_path->buf_idx) -
146 MEMCG_PATH_BUF_SIZE;
147 return &buf[idx];
148}
149
150static inline void put_memcg_path_buf(void)
151{
152 local_sub(MEMCG_PATH_BUF_SIZE, &this_cpu_ptr(&memcg_paths)->buf_idx);
153 rcu_read_unlock();
154}
155
156#define TRACE_MMAP_LOCK_EVENT(type, mm, ...) \
157 do { \
158 const char *memcg_path; \
159 local_lock(&memcg_paths.lock); \
160 memcg_path = get_mm_memcg_path(mm); \
161 trace_mmap_lock_##type(mm, \
162 memcg_path != NULL ? memcg_path : "", \
163 ##__VA_ARGS__); \
164 if (likely(memcg_path != NULL)) \
165 put_memcg_path_buf(); \
166 local_unlock(&memcg_paths.lock); \
167 } while (0)
168
169#else /* !CONFIG_MEMCG */
170
171int trace_mmap_lock_reg(void)
172{
173 return 0;
174}
175
176void trace_mmap_lock_unreg(void)
177{
178}
179
180#define TRACE_MMAP_LOCK_EVENT(type, mm, ...) \
181 trace_mmap_lock_##type(mm, "", ##__VA_ARGS__)
182
183#endif /* CONFIG_MEMCG */
184
185#ifdef CONFIG_TRACING
186#ifdef CONFIG_MEMCG
187/*
188 * Write the given mm_struct's memcg path to a percpu buffer, and return a
189 * pointer to it. If the path cannot be determined, or no buffer was available
190 * (because the trace event is being unregistered), NULL is returned.
191 *
192 * Note: buffers are allocated per-cpu to avoid locking, so preemption must be
193 * disabled by the caller before calling us, and re-enabled only after the
194 * caller is done with the pointer.
195 *
196 * The caller must call put_memcg_path_buf() once the buffer is no longer
197 * needed. This must be done while preemption is still disabled.
198 */
199static const char *get_mm_memcg_path(struct mm_struct *mm)
200{
201 char *buf = NULL;
202 struct mem_cgroup *memcg = get_mem_cgroup_from_mm(mm);
203
204 if (memcg == NULL)
205 goto out;
206 if (unlikely(memcg->css.cgroup == NULL))
207 goto out_put;
208
209 buf = get_memcg_path_buf();
210 if (buf == NULL)
211 goto out_put;
212
213 cgroup_path(memcg->css.cgroup, buf, MEMCG_PATH_BUF_SIZE);
214
215out_put:
216 css_put(&memcg->css);
217out:
218 return buf;
219}
220
221#endif /* CONFIG_MEMCG */
222
223/*
224 * Trace calls must be in a separate file, as otherwise there's a circular
225 * dependency between linux/mmap_lock.h and trace/events/mmap_lock.h.
226 */
227
228void __mmap_lock_do_trace_start_locking(struct mm_struct *mm, bool write)
229{
230 TRACE_MMAP_LOCK_EVENT(start_locking, mm, write);
231}
232EXPORT_SYMBOL(__mmap_lock_do_trace_start_locking);
233
234void __mmap_lock_do_trace_acquire_returned(struct mm_struct *mm, bool write,
235 bool success)
236{
237 TRACE_MMAP_LOCK_EVENT(acquire_returned, mm, write, success);
238}
239EXPORT_SYMBOL(__mmap_lock_do_trace_acquire_returned);
240
241void __mmap_lock_do_trace_released(struct mm_struct *mm, bool write)
242{
243 TRACE_MMAP_LOCK_EVENT(released, mm, write);
244}
245EXPORT_SYMBOL(__mmap_lock_do_trace_released);
246#endif /* CONFIG_TRACING */