Fix rmmod/read/write races in /proc entries

[pv_ops_mirror.git] / drivers / oprofile / buffer_sync.c

/**
 * @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/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 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 = 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.dentry,
                        vma->vm_file->f_path.mnt);
                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.dentry,
                                vma->vm_file->f_path.mnt);
                        *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 = &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);
}