// SPDX-License-Identifier: GPL-2.0
#define CREATE_TRACE_POINTS
#include <trace/events/mmap_lock.h>
#include <linux/mm.h>
#include <linux/cgroup.h>
#include <linux/memcontrol.h>
#include <linux/mmap_lock.h>
#include <linux/mutex.h>
#include <linux/percpu.h>
#include <linux/rcupdate.h>
#include <linux/smp.h>
#include <linux/trace_events.h>
#include <linux/local_lock.h>
EXPORT_TRACEPOINT_SYMBOL(mmap_lock_start_locking);
EXPORT_TRACEPOINT_SYMBOL(mmap_lock_acquire_returned);
EXPORT_TRACEPOINT_SYMBOL(mmap_lock_released);
#ifdef CONFIG_MEMCG
/*
* Our various events all share the same buffer (because we don't want or need
* to allocate a set of buffers *per event type*), so we need to protect against
* concurrent _reg() and _unreg() calls, and count how many _reg() calls have
* been made.
*/
static DEFINE_MUTEX(reg_lock);
static int reg_refcount; /* Protected by reg_lock. */
/*
* Size of the buffer for memcg path names. Ignoring stack trace support,
* trace_events_hist.c uses MAX_FILTER_STR_VAL for this, so we also use it.
*/
#define MEMCG_PATH_BUF_SIZE MAX_FILTER_STR_VAL
/*
* How many contexts our trace events might be called in: normal, softirq, irq,
* and NMI.
*/
#define CONTEXT_COUNT 4
struct memcg_path {
local_lock_t lock;
char __rcu *buf;
local_t buf_idx;
};
static DEFINE_PER_CPU(struct memcg_path, memcg_paths) = {
.lock = INIT_LOCAL_LOCK(lock),
.buf_idx = LOCAL_INIT(0),
};
static char **tmp_bufs;
/* Called with reg_lock held. */
static void free_memcg_path_bufs(void)
{
struct memcg_path *memcg_path;
int cpu;
char **old = tmp_bufs;
for_each_possible_cpu(cpu) {
memcg_path = per_cpu_ptr(&memcg_paths, cpu);
*(old++) = rcu_dereference_protected(memcg_path->buf,
lockdep_is_held(®_lock));
rcu_assign_pointer(memcg_path->buf, NULL);
}
/* Wait for inflight memcg_path_buf users to finish. */
synchronize_rcu();
old = tmp_bufs;
for_each_possible_cpu(cpu) {
kfree(*(old++));
}
kfree(tmp_bufs);
tmp_bufs = NULL;
}
int trace_mmap_lock_reg(void)
{
int cpu;
char *new;
mutex_lock(®_lock);
/* If the refcount is going 0->1, proceed with allocating buffers. */
if (reg_refcount++)
goto out;
tmp_bufs = kmalloc_array(num_possible_cpus(), sizeof(*tmp_bufs),
GFP_KERNEL);
if (tmp_bufs == NULL)
goto out_fail;
for_each_possible_cpu(cpu) {
new = kmalloc(MEMCG_PATH_BUF_SIZE * CONTEXT_COUNT, GFP_KERNEL);
if (new == NULL)
goto out_fail_free;
rcu_assign_pointer(per_cpu_ptr(&memcg_paths, cpu)->buf, new);
/* Don't need to wait for inflights, they'd have gotten NULL. */
}
out:
mutex_unlock(®_lock);
return 0;
out_fail_free:
free_memcg_path_bufs();
out_fail:
/* Since we failed, undo the earlier ref increment. */
--reg_refcount;
mutex_unlock(®_lock);
return -ENOMEM;
}
void trace_mmap_lock_unreg(void)
{
mutex_lock(®_lock);
/* If the refcount is going 1->0, proceed with freeing buffers. */
if (--reg_refcount)
goto out;
free_memcg_path_bufs();
out:
mutex_unlock(®_lock);
}
static inline char *get_memcg_path_buf(void)
{
struct memcg_path *memcg_path = this_cpu_ptr(&memcg_paths);
char *buf;
int idx;
rcu_read_lock();
buf = rcu_dereference(memcg_path->buf);
if (buf == NULL) {
rcu_read_unlock();
return NULL;
}
idx = local_add_return(MEMCG_PATH_BUF_SIZE, &memcg_path->buf_idx) -
MEMCG_PATH_BUF_SIZE;
return &buf[idx];
}
static inline void put_memcg_path_buf(void)
{
local_sub(MEMCG_PATH_BUF_SIZE, &this_cpu_ptr(&memcg_paths)->buf_idx);
rcu_read_unlock();
}
#define TRACE_MMAP_LOCK_EVENT(type, mm, ...) \
do { \
const char *memcg_path; \
local_lock(&memcg_paths.lock); \
memcg_path = get_mm_memcg_path(mm); \
trace_mmap_lock_##type(mm, \
memcg_path != NULL ? memcg_path : "", \
##__VA_ARGS__); \
if (likely(memcg_path != NULL)) \
put_memcg_path_buf(); \
local_unlock(&memcg_paths.lock); \
} while (0)
#else /* !CONFIG_MEMCG */
int trace_mmap_lock_reg(void)
{
return 0;
}
void trace_mmap_lock_unreg(void)
{
}
#define TRACE_MMAP_LOCK_EVENT(type, mm, ...) \
trace_mmap_lock_##type(mm, "", ##__VA_ARGS__)
#endif /* CONFIG_MEMCG */
#ifdef CONFIG_TRACING
#ifdef CONFIG_MEMCG
/*
* Write the given mm_struct's memcg path to a percpu buffer, and return a
* pointer to it. If the path cannot be determined, or no buffer was available
* (because the trace event is being unregistered), NULL is returned.
*
* Note: buffers are allocated per-cpu to avoid locking, so preemption must be
* disabled by the caller before calling us, and re-enabled only after the
* caller is done with the pointer.
*
* The caller must call put_memcg_path_buf() once the buffer is no longer
* needed. This must be done while preemption is still disabled.
*/
static const char *get_mm_memcg_path(struct mm_struct *mm)
{
char *buf = NULL;
struct mem_cgroup *memcg = get_mem_cgroup_from_mm(mm);
if (memcg == NULL)
goto out;
if (unlikely(memcg->css.cgroup == NULL))
goto out_put;
buf = get_memcg_path_buf();
if (buf == NULL)
goto out_put;
cgroup_path(memcg->css.cgroup, buf, MEMCG_PATH_BUF_SIZE);
out_put:
css_put(&memcg->css);
out:
return buf;
}
#endif /* CONFIG_MEMCG */
/*
* Trace calls must be in a separate file, as otherwise there's a circular
* dependency between linux/mmap_lock.h and trace/events/mmap_lock.h.
*/
void __mmap_lock_do_trace_start_locking(struct mm_struct *mm, bool write)
{
TRACE_MMAP_LOCK_EVENT(start_locking, mm, write);
}
EXPORT_SYMBOL(__mmap_lock_do_trace_start_locking);
void __mmap_lock_do_trace_acquire_returned(struct mm_struct *mm, bool write,
bool success)
{
TRACE_MMAP_LOCK_EVENT(acquire_returned, mm, write, success);
}
EXPORT_SYMBOL(__mmap_lock_do_trace_acquire_returned);
void __mmap_lock_do_trace_released(struct mm_struct *mm, bool write)
{
TRACE_MMAP_LOCK_EVENT(released, mm, write);
}
EXPORT_SYMBOL(__mmap_lock_do_trace_released);
#endif /* CONFIG_TRACING */
