drivers/oprofile/buffer_sync.c - kernel/msm - Gitiles

 /**
  * @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 "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.
  */
 static int task_free_notify(struct notifier_block * self, unsigned long val, void * data)
 {
 	struct task_struct * task = data;
 	spin_lock(&task_mortuary);
 	list_add(&task->tasks, &dying_tasks);
 	spin_unlock(&task_mortuary);
 	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 ? */
 	down(&buffer_sem);
 	add_event_entry(ESCAPE_CODE);
 	add_event_entry(MODULE_LOADED_CODE);
 	up(&buffer_sem);
 #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 dentry * dentry,
 	struct vfsmount * vfsmnt)
 {
 	unsigned long cookie;

 	if (dentry->d_cookie)
 		return (unsigned long)dentry;
 	get_dcookie(dentry, vfsmnt, &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 = 0;
 	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_dentry,
 			vma->vm_file->f_vfsmnt);
 		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 = 0;
 	struct vm_area_struct * vma;

 	for (vma = find_vma(mm, addr); vma; vma = vma->vm_next) {

 		if (!vma->vm_file)
 			continue;

 		if (addr < vma->vm_start || addr >= vma->vm_end)
 			continue;

 		cookie = fast_get_dcookie(vma->vm_file->f_dentry,
 			vma->vm_file->f_vfsmnt);
 		*offset = (vma->vm_pgoff << PAGE_SHIFT) + addr - vma->vm_start;
 		break;
 	}

 	return cookie;
 }


 static unsigned long last_cookie = ~0UL;

 static void add_cpu_switch(int i)
 {
 	add_event_entry(ESCAPE_CODE);
 	add_event_entry(CPU_SWITCH_CODE);
 	add_event_entry(i);
 	last_cookie = ~0UL;
 }

 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) {
 		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)
 {
 	struct list_head * pos;
 	struct list_head * pos2;
 	struct task_struct * task;

 	spin_lock(&task_mortuary);

 	list_for_each_safe(pos, pos2, &dead_tasks) {
 		task = list_entry(pos, struct task_struct, tasks);
 		list_del(&task->tasks);
 		free_task(task);
 	}

 	list_for_each_safe(pos, pos2, &dying_tasks) {
 		task = list_entry(pos, struct task_struct, tasks);
 		list_del(&task->tasks);
 		list_add_tail(&task->tasks, &dead_tasks);
 	}

 	spin_unlock(&task_mortuary);
 }


 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 = &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;

 	down(&buffer_sem);

 	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);

 	up(&buffer_sem);
 }
	/**
	* @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 "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.
	*/
	static int task_free_notify(struct notifier_block * self, unsigned long val, void * data)
	{
	struct task_struct * task = data;
	spin_lock(&task_mortuary);
	list_add(&task->tasks, &dying_tasks);
	spin_unlock(&task_mortuary);
	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 ? */
	down(&buffer_sem);
	add_event_entry(ESCAPE_CODE);
	add_event_entry(MODULE_LOADED_CODE);
	up(&buffer_sem);
	#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 dentry * dentry,
	struct vfsmount * vfsmnt)
	{
	unsigned long cookie;

	if (dentry->d_cookie)
	return (unsigned long)dentry;
	get_dcookie(dentry, vfsmnt, &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 = 0;
	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_dentry,
	vma->vm_file->f_vfsmnt);
	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 = 0;
	struct vm_area_struct * vma;

	for (vma = find_vma(mm, addr); vma; vma = vma->vm_next) {

	if (!vma->vm_file)
	continue;

	if (addr < vma->vm_start \|\| addr >= vma->vm_end)
	continue;

	cookie = fast_get_dcookie(vma->vm_file->f_dentry,
	vma->vm_file->f_vfsmnt);
	*offset = (vma->vm_pgoff << PAGE_SHIFT) + addr - vma->vm_start;
	break;
	}

	return cookie;
	}


	static unsigned long last_cookie = ~0UL;

	static void add_cpu_switch(int i)
	{
	add_event_entry(ESCAPE_CODE);
	add_event_entry(CPU_SWITCH_CODE);
	add_event_entry(i);
	last_cookie = ~0UL;
	}

	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) {
	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)
	{
	struct list_head * pos;
	struct list_head * pos2;
	struct task_struct * task;

	spin_lock(&task_mortuary);

	list_for_each_safe(pos, pos2, &dead_tasks) {
	task = list_entry(pos, struct task_struct, tasks);
	list_del(&task->tasks);
	free_task(task);
	}

	list_for_each_safe(pos, pos2, &dying_tasks) {
	task = list_entry(pos, struct task_struct, tasks);
	list_del(&task->tasks);
	list_add_tail(&task->tasks, &dead_tasks);
	}

	spin_unlock(&task_mortuary);
	}


	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 = &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;

	down(&buffer_sem);

	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);

	up(&buffer_sem);
	}