/**
   * @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/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 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_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;
  	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;
  }

  /* 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 = take_tasks_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);
  }