linux/drivers/oprofile/buffer_sync.c
Davidlohr Bueso 11163348a2 oprofile: reduce mmap_sem hold for mm->exe_file
sync_buffer() needs the mmap_sem for two distinct operations, both only
occurring upon user context switch handling:

 1) Dealing with the exe_file.

 2) Adding the dcookie data as we need to lookup the vma that
   backs it. This is done via add_sample() and add_data().

This patch isolates 1), for it will no longer need the mmap_sem for
serialization.  However, for now, make of the more standard
get_mm_exe_file(), requiring only holding the mmap_sem to read the value,
and relying on reference counting to make sure that the exe file won't
dissappear underneath us while doing the get dcookie.

As a consequence, for 2) we move the mmap_sem locking into where we really
need it, in lookup_dcookie().  The benefits are twofold: reduce mmap_sem
hold times, and cleaner code.

[akpm@linux-foundation.org: export get_mm_exe_file for arch/x86/oprofile/oprofile.ko]
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Robert Richter <rric@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-04-17 09:04:11 -04:00

590 lines
13 KiB
C

/**
* @file buffer_sync.c
*
* @remark Copyright 2002-2009 OProfile authors
* @remark Read the file COPYING
*
* @author John Levon <levon@movementarian.org>
* @author Barry Kasindorf
* @author Robert Richter <robert.richter@amd.com>
*
* 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/file.h>
#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 <linux/gfp.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_var_t marked_cpus;
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 free_all_tasks(void)
{
/* make sure we don't leak task structs */
process_task_mortuary();
process_task_mortuary();
}
int sync_start(void)
{
int err;
if (!zalloc_cpumask_var(&marked_cpus, GFP_KERNEL))
return -ENOMEM;
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;
start_cpu_work();
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);
free_all_tasks();
out1:
free_cpumask_var(marked_cpus);
goto out;
}
void sync_stop(void)
{
end_cpu_work();
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);
barrier(); /* do all of the above first */
flush_cpu_work();
free_all_tasks();
free_cpumask_var(marked_cpus);
}
/* 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_flags & DCACHE_COOKIE)
return (unsigned long)path->dentry;
get_dcookie(path, &cookie);
return cookie;
}
/* Look up the dcookie for the task's mm->exe_file,
* 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 file *exe_file;
if (!mm)
goto done;
exe_file = get_mm_exe_file(mm);
if (!exe_file)
goto done;
cookie = fast_get_dcookie(&exe_file->f_path);
fput(exe_file);
done:
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.
*
* The caller must ensure the mm is not nil (ie: not a kernel thread).
*/
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;
down_read(&mm->mmap_sem);
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;
up_read(&mm->mmap_sem);
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_data(struct op_entry *entry, struct mm_struct *mm)
{
unsigned long code, pc, val;
unsigned long cookie;
off_t offset;
if (!op_cpu_buffer_get_data(entry, &code))
return;
if (!op_cpu_buffer_get_data(entry, &pc))
return;
if (!op_cpu_buffer_get_size(entry))
return;
if (mm) {
cookie = lookup_dcookie(mm, pc, &offset);
if (cookie == NO_COOKIE)
offset = pc;
if (cookie == INVALID_COOKIE) {
atomic_inc(&oprofile_stats.sample_lost_no_mapping);
offset = pc;
}
if (cookie != last_cookie) {
add_cookie_switch(cookie);
last_cookie = cookie;
}
} else
offset = pc;
add_event_entry(ESCAPE_CODE);
add_event_entry(code);
add_event_entry(offset); /* Offset from Dcookie */
while (op_cpu_buffer_get_data(entry, &val))
add_event_entry(val);
}
static inline void add_sample_entry(unsigned long offset, unsigned long event)
{
add_event_entry(offset);
add_event_entry(event);
}
/*
* 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. Return 0 on failure.
*/
static int
add_sample(struct mm_struct *mm, struct op_sample *s, int in_kernel)
{
unsigned long cookie;
off_t offset;
if (in_kernel) {
add_sample_entry(s->eip, s->event);
return 1;
}
/* add userspace sample */
if (!mm) {
atomic_inc(&oprofile_stats.sample_lost_no_mm);
return 0;
}
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;
}
static void release_mm(struct mm_struct *mm)
{
if (!mm)
return;
mmput(mm);
}
static inline int is_code(unsigned long val)
{
return val == ESCAPE_CODE;
}
/* 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;
cpumask_set_cpu(cpu, marked_cpus);
for_each_online_cpu(i) {
if (!cpumask_test_cpu(i, marked_cpus))
return;
}
/* All CPUs have been processed at least once,
* we can process the mortuary once
*/
process_task_mortuary();
cpumask_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 mm_struct *mm = NULL;
struct mm_struct *oldmm;
unsigned long val;
struct task_struct *new;
unsigned long cookie = 0;
int in_kernel = 1;
sync_buffer_state state = sb_buffer_start;
unsigned int i;
unsigned long available;
unsigned long flags;
struct op_entry entry;
struct op_sample *sample;
mutex_lock(&buffer_mutex);
add_cpu_switch(cpu);
op_cpu_buffer_reset(cpu);
available = op_cpu_buffer_entries(cpu);
for (i = 0; i < available; ++i) {
sample = op_cpu_buffer_read_entry(&entry, cpu);
if (!sample)
break;
if (is_code(sample->eip)) {
flags = sample->event;
if (flags & TRACE_BEGIN) {
state = sb_bt_start;
add_trace_begin();
}
if (flags & KERNEL_CTX_SWITCH) {
/* kernel/userspace switch */
in_kernel = flags & IS_KERNEL;
if (state == sb_buffer_start)
state = sb_sample_start;
add_kernel_ctx_switch(flags & IS_KERNEL);
}
if (flags & USER_CTX_SWITCH
&& op_cpu_buffer_get_data(&entry, &val)) {
/* userspace context switch */
new = (struct task_struct *)val;
oldmm = mm;
release_mm(oldmm);
mm = get_task_mm(new);
if (mm != oldmm)
cookie = get_exec_dcookie(mm);
add_user_ctx_switch(new, cookie);
}
if (op_cpu_buffer_get_size(&entry))
add_data(&entry, mm);
continue;
}
if (state < sb_bt_start)
/* ignore sample */
continue;
if (add_sample(mm, sample, in_kernel))
continue;
/* ignore backtraces if failed to add a sample */
if (state == sb_bt_start) {
state = sb_bt_ignore;
atomic_inc(&oprofile_stats.bt_lost_no_mapping);
}
}
release_mm(mm);
mark_done(cpu);
mutex_unlock(&buffer_mutex);
}
/* The function can be used to add a buffer worth of data directly to
* the kernel buffer. The buffer is assumed to be a circular buffer.
* Take the entries from index start and end at index end, wrapping
* at max_entries.
*/
void oprofile_put_buff(unsigned long *buf, unsigned int start,
unsigned int stop, unsigned int max)
{
int i;
i = start;
mutex_lock(&buffer_mutex);
while (i != stop) {
add_event_entry(buf[i++]);
if (i >= max)
i = 0;
}
mutex_unlock(&buffer_mutex);
}