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linux/drivers/oprofile/buffer_sync.c

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/**
* @file buffer_sync.c
*
* @remark Copyright 2002 OProfile authors
* @remark Read the file COPYING
*
* @author John Levon <levon@movementarian.org>
*
* This is the core of the buffer management. Each
* CPU buffer is processed and entered into the
* global event buffer. Such processing is necessary
* in several circumstances, mentioned below.
*
* The processing does the job of converting the
* transitory EIP value into a persistent dentry/offset
* value that the profiler can record at its leisure.
*
* See fs/dcookies.c for a description of the dentry/offset
* objects.
*/
#include <linux/mm.h>
#include <linux/workqueue.h>
#include <linux/notifier.h>
#include <linux/dcookies.h>
#include <linux/profile.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/oprofile.h>
#include <linux/sched.h>
#include "oprofile_stats.h"
#include "event_buffer.h"
#include "cpu_buffer.h"
#include "buffer_sync.h"
static LIST_HEAD(dying_tasks);
static LIST_HEAD(dead_tasks);
static cpumask_t marked_cpus = CPU_MASK_NONE;
static DEFINE_SPINLOCK(task_mortuary);
static void process_task_mortuary(void);
/* Take ownership of the task struct and place it on the
* list for processing. Only after two full buffer syncs
* does the task eventually get freed, because by then
* we are sure we will not reference it again.
* Can be invoked from softirq via RCU callback due to
* call_rcu() of the task struct, hence the _irqsave.
*/
static int task_free_notify(struct notifier_block * self, unsigned long val, void * data)
{
unsigned long flags;
struct task_struct * task = data;
spin_lock_irqsave(&task_mortuary, flags);
list_add(&task->tasks, &dying_tasks);
spin_unlock_irqrestore(&task_mortuary, flags);
return NOTIFY_OK;
}
/* The task is on its way out. A sync of the buffer means we can catch
* any remaining samples for this task.
*/
static int task_exit_notify(struct notifier_block * self, unsigned long val, void * data)
{
/* To avoid latency problems, we only process the current CPU,
* hoping that most samples for the task are on this CPU
*/
sync_buffer(raw_smp_processor_id());
return 0;
}
/* The task is about to try a do_munmap(). We peek at what it's going to
* do, and if it's an executable region, process the samples first, so
* we don't lose any. This does not have to be exact, it's a QoI issue
* only.
*/
static int munmap_notify(struct notifier_block * self, unsigned long val, void * data)
{
unsigned long addr = (unsigned long)data;
struct mm_struct * mm = current->mm;
struct vm_area_struct * mpnt;
down_read(&mm->mmap_sem);
mpnt = find_vma(mm, addr);
if (mpnt && mpnt->vm_file && (mpnt->vm_flags & VM_EXEC)) {
up_read(&mm->mmap_sem);
/* To avoid latency problems, we only process the current CPU,
* hoping that most samples for the task are on this CPU
*/
sync_buffer(raw_smp_processor_id());
return 0;
}
up_read(&mm->mmap_sem);
return 0;
}
/* We need to be told about new modules so we don't attribute to a previously
* loaded module, or drop the samples on the floor.
*/
static int module_load_notify(struct notifier_block * self, unsigned long val, void * data)
{
#ifdef CONFIG_MODULES
if (val != MODULE_STATE_COMING)
return 0;
/* FIXME: should we process all CPU buffers ? */
mutex_lock(&buffer_mutex);
add_event_entry(ESCAPE_CODE);
add_event_entry(MODULE_LOADED_CODE);
mutex_unlock(&buffer_mutex);
#endif
return 0;
}
static struct notifier_block task_free_nb = {
.notifier_call = task_free_notify,
};
static struct notifier_block task_exit_nb = {
.notifier_call = task_exit_notify,
};
static struct notifier_block munmap_nb = {
.notifier_call = munmap_notify,
};
static struct notifier_block module_load_nb = {
.notifier_call = module_load_notify,
};
static void end_sync(void)
{
end_cpu_work();
/* make sure we don't leak task structs */
process_task_mortuary();
process_task_mortuary();
}
int sync_start(void)
{
int err;
start_cpu_work();
err = task_handoff_register(&task_free_nb);
if (err)
goto out1;
err = profile_event_register(PROFILE_TASK_EXIT, &task_exit_nb);
if (err)
goto out2;
err = profile_event_register(PROFILE_MUNMAP, &munmap_nb);
if (err)
goto out3;
err = register_module_notifier(&module_load_nb);
if (err)
goto out4;
out:
return err;
out4:
profile_event_unregister(PROFILE_MUNMAP, &munmap_nb);
out3:
profile_event_unregister(PROFILE_TASK_EXIT, &task_exit_nb);
out2:
task_handoff_unregister(&task_free_nb);
out1:
end_sync();
goto out;
}
void sync_stop(void)
{
unregister_module_notifier(&module_load_nb);
profile_event_unregister(PROFILE_MUNMAP, &munmap_nb);
profile_event_unregister(PROFILE_TASK_EXIT, &task_exit_nb);
task_handoff_unregister(&task_free_nb);
end_sync();
}
/* Optimisation. We can manage without taking the dcookie sem
* because we cannot reach this code without at least one
* dcookie user still being registered (namely, the reader
* of the event buffer). */
static inline unsigned long fast_get_dcookie(struct path *path)
{
unsigned long cookie;
if (path->dentry->d_cookie)
return (unsigned long)path->dentry;
get_dcookie(path, &cookie);
return cookie;
}
/* Look up the dcookie for the task's first VM_EXECUTABLE mapping,
* which corresponds loosely to "application name". This is
* not strictly necessary but allows oprofile to associate
* shared-library samples with particular applications
*/
static unsigned long get_exec_dcookie(struct mm_struct * mm)
{
unsigned long cookie = NO_COOKIE;
struct vm_area_struct * vma;
if (!mm)
goto out;
for (vma = mm->mmap; vma; vma = vma->vm_next) {
if (!vma->vm_file)
continue;
if (!(vma->vm_flags & VM_EXECUTABLE))
continue;
cookie = fast_get_dcookie(&vma->vm_file->f_path);
break;
}
out:
return cookie;
}
/* Convert the EIP value of a sample into a persistent dentry/offset
* pair that can then be added to the global event buffer. We make
* sure to do this lookup before a mm->mmap modification happens so
* we don't lose track.
*/
static unsigned long lookup_dcookie(struct mm_struct * mm, unsigned long addr, off_t * offset)
{
unsigned long cookie = NO_COOKIE;
struct vm_area_struct * vma;
for (vma = find_vma(mm, addr); vma; vma = vma->vm_next) {
if (addr < vma->vm_start || addr >= vma->vm_end)
continue;
if (vma->vm_file) {
cookie = fast_get_dcookie(&vma->vm_file->f_path);
*offset = (vma->vm_pgoff << PAGE_SHIFT) + addr -
vma->vm_start;
} else {
/* must be an anonymous map */
*offset = addr;
}
break;
}
if (!vma)
cookie = INVALID_COOKIE;
return cookie;
}
static unsigned long last_cookie = INVALID_COOKIE;
static void add_cpu_switch(int i)
{
add_event_entry(ESCAPE_CODE);
add_event_entry(CPU_SWITCH_CODE);
add_event_entry(i);
last_cookie = INVALID_COOKIE;
}
static void add_kernel_ctx_switch(unsigned int in_kernel)
{
add_event_entry(ESCAPE_CODE);
if (in_kernel)
add_event_entry(KERNEL_ENTER_SWITCH_CODE);
else
add_event_entry(KERNEL_EXIT_SWITCH_CODE);
}
static void
add_user_ctx_switch(struct task_struct const * task, unsigned long cookie)
{
add_event_entry(ESCAPE_CODE);
add_event_entry(CTX_SWITCH_CODE);
add_event_entry(task->pid);
add_event_entry(cookie);
/* Another code for daemon back-compat */
add_event_entry(ESCAPE_CODE);
add_event_entry(CTX_TGID_CODE);
add_event_entry(task->tgid);
}
static void add_cookie_switch(unsigned long cookie)
{
add_event_entry(ESCAPE_CODE);
add_event_entry(COOKIE_SWITCH_CODE);
add_event_entry(cookie);
}
static void add_trace_begin(void)
{
add_event_entry(ESCAPE_CODE);
add_event_entry(TRACE_BEGIN_CODE);
}
static void add_sample_entry(unsigned long offset, unsigned long event)
{
add_event_entry(offset);
add_event_entry(event);
}
static int add_us_sample(struct mm_struct * mm, struct op_sample * s)
{
unsigned long cookie;
off_t offset;
cookie = lookup_dcookie(mm, s->eip, &offset);
if (cookie == INVALID_COOKIE) {
atomic_inc(&oprofile_stats.sample_lost_no_mapping);
return 0;
}
if (cookie != last_cookie) {
add_cookie_switch(cookie);
last_cookie = cookie;
}
add_sample_entry(offset, s->event);
return 1;
}
/* Add a sample to the global event buffer. If possible the
* sample is converted into a persistent dentry/offset pair
* for later lookup from userspace.
*/
static int
add_sample(struct mm_struct * mm, struct op_sample * s, int in_kernel)
{
if (in_kernel) {
add_sample_entry(s->eip, s->event);
return 1;
} else if (mm) {
return add_us_sample(mm, s);
} else {
atomic_inc(&oprofile_stats.sample_lost_no_mm);
}
return 0;
}
static void release_mm(struct mm_struct * mm)
{
if (!mm)
return;
up_read(&mm->mmap_sem);
mmput(mm);
}
static struct mm_struct * take_tasks_mm(struct task_struct * task)
{
struct mm_struct * mm = get_task_mm(task);
if (mm)
down_read(&mm->mmap_sem);
return mm;
}
static inline int is_code(unsigned long val)
{
return val == ESCAPE_CODE;
}
/* "acquire" as many cpu buffer slots as we can */
static unsigned long get_slots(struct oprofile_cpu_buffer * b)
{
unsigned long head = b->head_pos;
unsigned long tail = b->tail_pos;
/*
* Subtle. This resets the persistent last_task
* and in_kernel values used for switching notes.
* BUT, there is a small window between reading
* head_pos, and this call, that means samples
* can appear at the new head position, but not
* be prefixed with the notes for switching
* kernel mode or a task switch. This small hole
* can lead to mis-attribution or samples where
* we don't know if it's in the kernel or not,
* at the start of an event buffer.
*/
cpu_buffer_reset(b);
if (head >= tail)
return head - tail;
return head + (b->buffer_size - tail);
}
static void increment_tail(struct oprofile_cpu_buffer * b)
{
unsigned long new_tail = b->tail_pos + 1;
rmb();
if (new_tail < b->buffer_size)
b->tail_pos = new_tail;
else
b->tail_pos = 0;
}
/* Move tasks along towards death. Any tasks on dead_tasks
* will definitely have no remaining references in any
* CPU buffers at this point, because we use two lists,
* and to have reached the list, it must have gone through
* one full sync already.
*/
static void process_task_mortuary(void)
{
unsigned long flags;
LIST_HEAD(local_dead_tasks);
struct task_struct * task;
struct task_struct * ttask;
spin_lock_irqsave(&task_mortuary, flags);
list_splice_init(&dead_tasks, &local_dead_tasks);
list_splice_init(&dying_tasks, &dead_tasks);
spin_unlock_irqrestore(&task_mortuary, flags);
list_for_each_entry_safe(task, ttask, &local_dead_tasks, tasks) {
list_del(&task->tasks);
free_task(task);
}
}
static void mark_done(int cpu)
{
int i;
cpu_set(cpu, marked_cpus);
for_each_online_cpu(i) {
if (!cpu_isset(i, marked_cpus))
return;
}
/* All CPUs have been processed at least once,
* we can process the mortuary once
*/
process_task_mortuary();
cpus_clear(marked_cpus);
}
/* FIXME: this is not sufficient if we implement syscall barrier backtrace
* traversal, the code switch to sb_sample_start at first kernel enter/exit
* switch so we need a fifth state and some special handling in sync_buffer()
*/
typedef enum {
sb_bt_ignore = -2,
sb_buffer_start,
sb_bt_start,
sb_sample_start,
} sync_buffer_state;
/* Sync one of the CPU's buffers into the global event buffer.
* Here we need to go through each batch of samples punctuated
* by context switch notes, taking the task's mmap_sem and doing
* lookup in task->mm->mmap to convert EIP into dcookie/offset
* value.
*/
void sync_buffer(int cpu)
{
struct oprofile_cpu_buffer *cpu_buf = &per_cpu(cpu_buffer, cpu);
struct mm_struct *mm = NULL;
struct task_struct * new;
unsigned long cookie = 0;
int in_kernel = 1;
unsigned int i;
sync_buffer_state state = sb_buffer_start;
unsigned long available;
mutex_lock(&buffer_mutex);
add_cpu_switch(cpu);
/* Remember, only we can modify tail_pos */
available = get_slots(cpu_buf);
for (i = 0; i < available; ++i) {
struct op_sample * s = &cpu_buf->buffer[cpu_buf->tail_pos];
if (is_code(s->eip)) {
if (s->event <= CPU_IS_KERNEL) {
/* kernel/userspace switch */
in_kernel = s->event;
if (state == sb_buffer_start)
state = sb_sample_start;
add_kernel_ctx_switch(s->event);
} else if (s->event == CPU_TRACE_BEGIN) {
state = sb_bt_start;
add_trace_begin();
} else {
struct mm_struct * oldmm = mm;
/* userspace context switch */
new = (struct task_struct *)s->event;
release_mm(oldmm);
mm = take_tasks_mm(new);
if (mm != oldmm)
cookie = get_exec_dcookie(mm);
add_user_ctx_switch(new, cookie);
}
} else {
if (state >= sb_bt_start &&
!add_sample(mm, s, in_kernel)) {
if (state == sb_bt_start) {
state = sb_bt_ignore;
atomic_inc(&oprofile_stats.bt_lost_no_mapping);
}
}
}
increment_tail(cpu_buf);
}
release_mm(mm);
mark_done(cpu);
mutex_unlock(&buffer_mutex);
}