Merge branch 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...
[safe/jmp/linux-2.6] / kernel / trace / ftrace.c
index ddf23a2..8378357 100644 (file)
@@ -22,7 +22,6 @@
 #include <linux/hardirq.h>
 #include <linux/kthread.h>
 #include <linux/uaccess.h>
-#include <linux/kprobes.h>
 #include <linux/ftrace.h>
 #include <linux/sysctl.h>
 #include <linux/ctype.h>
@@ -60,6 +59,13 @@ static int last_ftrace_enabled;
 /* Quick disabling of function tracer. */
 int function_trace_stop;
 
+/* List for set_ftrace_pid's pids. */
+LIST_HEAD(ftrace_pids);
+struct ftrace_pid {
+       struct list_head list;
+       struct pid *pid;
+};
+
 /*
  * ftrace_disabled is set when an anomaly is discovered.
  * ftrace_disabled is much stronger than ftrace_enabled.
@@ -78,6 +84,10 @@ ftrace_func_t ftrace_trace_function __read_mostly = ftrace_stub;
 ftrace_func_t __ftrace_trace_function __read_mostly = ftrace_stub;
 ftrace_func_t ftrace_pid_function __read_mostly = ftrace_stub;
 
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+static int ftrace_set_func(unsigned long *array, int *idx, char *buffer);
+#endif
+
 static void ftrace_list_func(unsigned long ip, unsigned long parent_ip)
 {
        struct ftrace_ops *op = ftrace_list;
@@ -155,7 +165,7 @@ static int __register_ftrace_function(struct ftrace_ops *ops)
                else
                        func = ftrace_list_func;
 
-               if (ftrace_pid_trace) {
+               if (!list_empty(&ftrace_pids)) {
                        set_ftrace_pid_function(func);
                        func = ftrace_pid_func;
                }
@@ -203,7 +213,7 @@ static int __unregister_ftrace_function(struct ftrace_ops *ops)
                if (ftrace_list->next == &ftrace_list_end) {
                        ftrace_func_t func = ftrace_list->func;
 
-                       if (ftrace_pid_trace) {
+                       if (!list_empty(&ftrace_pids)) {
                                set_ftrace_pid_function(func);
                                func = ftrace_pid_func;
                        }
@@ -225,9 +235,13 @@ static void ftrace_update_pid_func(void)
        if (ftrace_trace_function == ftrace_stub)
                return;
 
+#ifdef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
        func = ftrace_trace_function;
+#else
+       func = __ftrace_trace_function;
+#endif
 
-       if (ftrace_pid_trace) {
+       if (!list_empty(&ftrace_pids)) {
                set_ftrace_pid_function(func);
                func = ftrace_pid_func;
        } else {
@@ -736,7 +750,7 @@ ftrace_profile_write(struct file *filp, const char __user *ubuf,
  out:
        mutex_unlock(&ftrace_profile_lock);
 
-       filp->f_pos += cnt;
+       *ppos += cnt;
 
        return cnt;
 }
@@ -817,8 +831,6 @@ static __init void ftrace_profile_debugfs(struct dentry *d_tracer)
 }
 #endif /* CONFIG_FUNCTION_PROFILER */
 
-/* set when tracing only a pid */
-struct pid *ftrace_pid_trace;
 static struct pid * const ftrace_swapper_pid = &init_struct_pid;
 
 #ifdef CONFIG_DYNAMIC_FTRACE
@@ -885,36 +897,6 @@ static struct dyn_ftrace *ftrace_free_records;
                }                               \
        }
 
-#ifdef CONFIG_KPROBES
-
-static int frozen_record_count;
-
-static inline void freeze_record(struct dyn_ftrace *rec)
-{
-       if (!(rec->flags & FTRACE_FL_FROZEN)) {
-               rec->flags |= FTRACE_FL_FROZEN;
-               frozen_record_count++;
-       }
-}
-
-static inline void unfreeze_record(struct dyn_ftrace *rec)
-{
-       if (rec->flags & FTRACE_FL_FROZEN) {
-               rec->flags &= ~FTRACE_FL_FROZEN;
-               frozen_record_count--;
-       }
-}
-
-static inline int record_frozen(struct dyn_ftrace *rec)
-{
-       return rec->flags & FTRACE_FL_FROZEN;
-}
-#else
-# define freeze_record(rec)                    ({ 0; })
-# define unfreeze_record(rec)                  ({ 0; })
-# define record_frozen(rec)                    ({ 0; })
-#endif /* CONFIG_KPROBES */
-
 static void ftrace_free_rec(struct dyn_ftrace *rec)
 {
        rec->freelist = ftrace_free_records;
@@ -1012,6 +994,21 @@ static void ftrace_bug(int failed, unsigned long ip)
 }
 
 
+/* Return 1 if the address range is reserved for ftrace */
+int ftrace_text_reserved(void *start, void *end)
+{
+       struct dyn_ftrace *rec;
+       struct ftrace_page *pg;
+
+       do_for_each_ftrace_rec(pg, rec) {
+               if (rec->ip <= (unsigned long)end &&
+                   rec->ip + MCOUNT_INSN_SIZE > (unsigned long)start)
+                       return 1;
+       } while_for_each_ftrace_rec();
+       return 0;
+}
+
+
 static int
 __ftrace_replace_code(struct dyn_ftrace *rec, int enable)
 {
@@ -1063,25 +1060,12 @@ static void ftrace_replace_code(int enable)
                    !(rec->flags & FTRACE_FL_CONVERTED))
                        continue;
 
-               /* ignore updates to this record's mcount site */
-               if (get_kprobe((void *)rec->ip)) {
-                       freeze_record(rec);
-                       continue;
-               } else {
-                       unfreeze_record(rec);
-               }
-
                failed = __ftrace_replace_code(rec, enable);
                if (failed) {
                        rec->flags |= FTRACE_FL_FAILED;
-                       if ((system_state == SYSTEM_BOOTING) ||
-                           !core_kernel_text(rec->ip)) {
-                               ftrace_free_rec(rec);
-                               } else {
-                               ftrace_bug(failed, rec->ip);
-                                       /* Stop processing */
-                                       return;
-                               }
+                       ftrace_bug(failed, rec->ip);
+                       /* Stop processing */
+                       return;
                }
        } while_for_each_ftrace_rec();
 }
@@ -1262,12 +1246,34 @@ static int ftrace_update_code(struct module *mod)
                ftrace_new_addrs = p->newlist;
                p->flags = 0L;
 
-               /* convert record (i.e, patch mcount-call with NOP) */
-               if (ftrace_code_disable(mod, p)) {
-                       p->flags |= FTRACE_FL_CONVERTED;
-                       ftrace_update_cnt++;
-               } else
+               /*
+                * Do the initial record convertion from mcount jump
+                * to the NOP instructions.
+                */
+               if (!ftrace_code_disable(mod, p)) {
                        ftrace_free_rec(p);
+                       continue;
+               }
+
+               p->flags |= FTRACE_FL_CONVERTED;
+               ftrace_update_cnt++;
+
+               /*
+                * If the tracing is enabled, go ahead and enable the record.
+                *
+                * The reason not to enable the record immediatelly is the
+                * inherent check of ftrace_make_nop/ftrace_make_call for
+                * correct previous instructions.  Making first the NOP
+                * conversion puts the module to the correct state, thus
+                * passing the ftrace_make_call check.
+                */
+               if (ftrace_start_up) {
+                       int failed = __ftrace_replace_code(p, 1);
+                       if (failed) {
+                               ftrace_bug(failed, p->ip);
+                               ftrace_free_rec(p);
+                       }
+               }
        }
 
        stop = ftrace_now(raw_smp_processor_id());
@@ -1520,7 +1526,7 @@ static int t_show(struct seq_file *m, void *v)
        return 0;
 }
 
-static struct seq_operations show_ftrace_seq_ops = {
+static const struct seq_operations show_ftrace_seq_ops = {
        .start = t_start,
        .next = t_next,
        .stop = t_stop,
@@ -1621,8 +1627,10 @@ ftrace_regex_open(struct inode *inode, struct file *file, int enable)
                if (!ret) {
                        struct seq_file *m = file->private_data;
                        m->private = iter;
-               } else
+               } else {
+                       trace_parser_put(&iter->parser);
                        kfree(iter);
+               }
        } else
                file->private_data = iter;
        mutex_unlock(&ftrace_regex_lock);
@@ -1658,7 +1666,7 @@ ftrace_regex_lseek(struct file *file, loff_t offset, int origin)
 static int ftrace_match(char *str, char *regex, int len, int type)
 {
        int matched = 0;
-       char *ptr;
+       int slen;
 
        switch (type) {
        case MATCH_FULL:
@@ -1674,8 +1682,8 @@ static int ftrace_match(char *str, char *regex, int len, int type)
                        matched = 1;
                break;
        case MATCH_END_ONLY:
-               ptr = strstr(str, regex);
-               if (ptr && (ptr[len] == 0))
+               slen = strlen(str);
+               if (slen >= len && memcmp(str + slen - len, regex, len) == 0)
                        matched = 1;
                break;
        }
@@ -1692,7 +1700,7 @@ ftrace_match_record(struct dyn_ftrace *rec, char *regex, int len, int type)
        return ftrace_match(str, regex, len, type);
 }
 
-static void ftrace_match_records(char *buff, int len, int enable)
+static int ftrace_match_records(char *buff, int len, int enable)
 {
        unsigned int search_len;
        struct ftrace_page *pg;
@@ -1701,6 +1709,7 @@ static void ftrace_match_records(char *buff, int len, int enable)
        char *search;
        int type;
        int not;
+       int found = 0;
 
        flag = enable ? FTRACE_FL_FILTER : FTRACE_FL_NOTRACE;
        type = filter_parse_regex(buff, len, &search, &not);
@@ -1718,6 +1727,7 @@ static void ftrace_match_records(char *buff, int len, int enable)
                                rec->flags &= ~flag;
                        else
                                rec->flags |= flag;
+                       found = 1;
                }
                /*
                 * Only enable filtering if we have a function that
@@ -1727,6 +1737,8 @@ static void ftrace_match_records(char *buff, int len, int enable)
                        ftrace_filtered = 1;
        } while_for_each_ftrace_rec();
        mutex_unlock(&ftrace_lock);
+
+       return found;
 }
 
 static int
@@ -1748,7 +1760,7 @@ ftrace_match_module_record(struct dyn_ftrace *rec, char *mod,
                return 1;
 }
 
-static void ftrace_match_module_records(char *buff, char *mod, int enable)
+static int ftrace_match_module_records(char *buff, char *mod, int enable)
 {
        unsigned search_len = 0;
        struct ftrace_page *pg;
@@ -1757,6 +1769,7 @@ static void ftrace_match_module_records(char *buff, char *mod, int enable)
        char *search = buff;
        unsigned long flag;
        int not = 0;
+       int found = 0;
 
        flag = enable ? FTRACE_FL_FILTER : FTRACE_FL_NOTRACE;
 
@@ -1787,12 +1800,15 @@ static void ftrace_match_module_records(char *buff, char *mod, int enable)
                                rec->flags &= ~flag;
                        else
                                rec->flags |= flag;
+                       found = 1;
                }
                if (enable && (rec->flags & FTRACE_FL_FILTER))
                        ftrace_filtered = 1;
 
        } while_for_each_ftrace_rec();
        mutex_unlock(&ftrace_lock);
+
+       return found;
 }
 
 /*
@@ -1821,8 +1837,9 @@ ftrace_mod_callback(char *func, char *cmd, char *param, int enable)
        if (!strlen(mod))
                return -EINVAL;
 
-       ftrace_match_module_records(func, mod, enable);
-       return 0;
+       if (ftrace_match_module_records(func, mod, enable))
+               return 0;
+       return -EINVAL;
 }
 
 static struct ftrace_func_command ftrace_mod_cmd = {
@@ -2119,8 +2136,9 @@ static int ftrace_process_regex(char *buff, int len, int enable)
        func = strsep(&next, ":");
 
        if (!next) {
-               ftrace_match_records(func, len, enable);
-               return 0;
+               if (ftrace_match_records(func, len, enable))
+                       return 0;
+               return ret;
        }
 
        /* command found */
@@ -2148,7 +2166,7 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
        struct trace_parser *parser;
        ssize_t ret, read;
 
-       if (!cnt || cnt < 0)
+       if (!cnt)
                return 0;
 
        mutex_lock(&ftrace_regex_lock);
@@ -2162,20 +2180,19 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
        parser = &iter->parser;
        read = trace_get_user(parser, ubuf, cnt, ppos);
 
-       if (trace_parser_loaded(parser) &&
+       if (read >= 0 && trace_parser_loaded(parser) &&
            !trace_parser_cont(parser)) {
                ret = ftrace_process_regex(parser->buffer,
                                           parser->idx, enable);
-               if (ret)
-                       goto out;
-
                trace_parser_clear(parser);
+               if (ret)
+                       goto out_unlock;
        }
 
        ret = read;
-
+out_unlock:
        mutex_unlock(&ftrace_regex_lock);
-out:
+
        return ret;
 }
 
@@ -2257,6 +2274,32 @@ static int __init set_ftrace_filter(char *str)
 }
 __setup("ftrace_filter=", set_ftrace_filter);
 
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+static char ftrace_graph_buf[FTRACE_FILTER_SIZE] __initdata;
+static int __init set_graph_function(char *str)
+{
+       strlcpy(ftrace_graph_buf, str, FTRACE_FILTER_SIZE);
+       return 1;
+}
+__setup("ftrace_graph_filter=", set_graph_function);
+
+static void __init set_ftrace_early_graph(char *buf)
+{
+       int ret;
+       char *func;
+
+       while (buf) {
+               func = strsep(&buf, ",");
+               /* we allow only one expression at a time */
+               ret = ftrace_set_func(ftrace_graph_funcs, &ftrace_graph_count,
+                                     func);
+               if (ret)
+                       printk(KERN_DEBUG "ftrace: function %s not "
+                                         "traceable\n", func);
+       }
+}
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
 static void __init set_ftrace_early_filter(char *buf, int enable)
 {
        char *func;
@@ -2273,6 +2316,10 @@ static void __init set_ftrace_early_filters(void)
                set_ftrace_early_filter(ftrace_filter_buf, 1);
        if (ftrace_notrace_buf[0])
                set_ftrace_early_filter(ftrace_notrace_buf, 0);
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+       if (ftrace_graph_buf[0])
+               set_ftrace_early_graph(ftrace_graph_buf);
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 }
 
 static int
@@ -2355,16 +2402,15 @@ static const struct file_operations ftrace_notrace_fops = {
 static DEFINE_MUTEX(graph_lock);
 
 int ftrace_graph_count;
+int ftrace_graph_filter_enabled;
 unsigned long ftrace_graph_funcs[FTRACE_GRAPH_MAX_FUNCS] __read_mostly;
 
 static void *
 __g_next(struct seq_file *m, loff_t *pos)
 {
-       unsigned long *array = m->private;
-
        if (*pos >= ftrace_graph_count)
                return NULL;
-       return &array[*pos];
+       return &ftrace_graph_funcs[*pos];
 }
 
 static void *
@@ -2379,7 +2425,7 @@ static void *g_start(struct seq_file *m, loff_t *pos)
        mutex_lock(&graph_lock);
 
        /* Nothing, tell g_show to print all functions are enabled */
-       if (!ftrace_graph_count && !*pos)
+       if (!ftrace_graph_filter_enabled && !*pos)
                return (void *)1;
 
        return __g_next(m, pos);
@@ -2407,7 +2453,7 @@ static int g_show(struct seq_file *m, void *v)
        return 0;
 }
 
-static struct seq_operations ftrace_graph_seq_ops = {
+static const struct seq_operations ftrace_graph_seq_ops = {
        .start = g_start,
        .next = g_next,
        .stop = g_stop,
@@ -2425,19 +2471,14 @@ ftrace_graph_open(struct inode *inode, struct file *file)
        mutex_lock(&graph_lock);
        if ((file->f_mode & FMODE_WRITE) &&
            (file->f_flags & O_TRUNC)) {
+               ftrace_graph_filter_enabled = 0;
                ftrace_graph_count = 0;
                memset(ftrace_graph_funcs, 0, sizeof(ftrace_graph_funcs));
        }
+       mutex_unlock(&graph_lock);
 
-       if (file->f_mode & FMODE_READ) {
+       if (file->f_mode & FMODE_READ)
                ret = seq_open(file, &ftrace_graph_seq_ops);
-               if (!ret) {
-                       struct seq_file *m = file->private_data;
-                       m->private = ftrace_graph_funcs;
-               }
-       } else
-               file->private_data = ftrace_graph_funcs;
-       mutex_unlock(&graph_lock);
 
        return ret;
 }
@@ -2456,7 +2497,7 @@ ftrace_set_func(unsigned long *array, int *idx, char *buffer)
        struct dyn_ftrace *rec;
        struct ftrace_page *pg;
        int search_len;
-       int found = 0;
+       int fail = 1;
        int type, not;
        char *search;
        bool exists;
@@ -2467,38 +2508,51 @@ ftrace_set_func(unsigned long *array, int *idx, char *buffer)
 
        /* decode regex */
        type = filter_parse_regex(buffer, strlen(buffer), &search, &not);
-       if (not)
-               return -EINVAL;
+       if (!not && *idx >= FTRACE_GRAPH_MAX_FUNCS)
+               return -EBUSY;
 
        search_len = strlen(search);
 
        mutex_lock(&ftrace_lock);
        do_for_each_ftrace_rec(pg, rec) {
 
-               if (*idx >= FTRACE_GRAPH_MAX_FUNCS)
-                       break;
-
                if (rec->flags & (FTRACE_FL_FAILED | FTRACE_FL_FREE))
                        continue;
 
                if (ftrace_match_record(rec, search, search_len, type)) {
-                       /* ensure it is not already in the array */
+                       /* if it is in the array */
                        exists = false;
-                       for (i = 0; i < *idx; i++)
+                       for (i = 0; i < *idx; i++) {
                                if (array[i] == rec->ip) {
                                        exists = true;
                                        break;
                                }
-                       if (!exists) {
-                               array[(*idx)++] = rec->ip;
-                               found = 1;
+                       }
+
+                       if (!not) {
+                               fail = 0;
+                               if (!exists) {
+                                       array[(*idx)++] = rec->ip;
+                                       if (*idx >= FTRACE_GRAPH_MAX_FUNCS)
+                                               goto out;
+                               }
+                       } else {
+                               if (exists) {
+                                       array[i] = array[--(*idx)];
+                                       array[*idx] = 0;
+                                       fail = 0;
+                               }
                        }
                }
        } while_for_each_ftrace_rec();
-
+out:
        mutex_unlock(&ftrace_lock);
 
-       return found ? 0 : -EINVAL;
+       if (fail)
+               return -EINVAL;
+
+       ftrace_graph_filter_enabled = 1;
+       return 0;
 }
 
 static ssize_t
@@ -2506,46 +2560,35 @@ ftrace_graph_write(struct file *file, const char __user *ubuf,
                   size_t cnt, loff_t *ppos)
 {
        struct trace_parser parser;
-       unsigned long *array;
-       size_t read = 0;
-       ssize_t ret;
+       ssize_t read, ret;
 
-       if (!cnt || cnt < 0)
+       if (!cnt)
                return 0;
 
        mutex_lock(&graph_lock);
 
-       if (ftrace_graph_count >= FTRACE_GRAPH_MAX_FUNCS) {
-               ret = -EBUSY;
-               goto out;
-       }
-
-       if (file->f_mode & FMODE_READ) {
-               struct seq_file *m = file->private_data;
-               array = m->private;
-       } else
-               array = file->private_data;
-
        if (trace_parser_get_init(&parser, FTRACE_BUFF_MAX)) {
                ret = -ENOMEM;
-               goto out;
+               goto out_unlock;
        }
 
        read = trace_get_user(&parser, ubuf, cnt, ppos);
 
-       if (trace_parser_loaded((&parser))) {
+       if (read >= 0 && trace_parser_loaded((&parser))) {
                parser.buffer[parser.idx] = 0;
 
                /* we allow only one expression at a time */
-               ret = ftrace_set_func(array, &ftrace_graph_count,
+               ret = ftrace_set_func(ftrace_graph_funcs, &ftrace_graph_count,
                                        parser.buffer);
                if (ret)
-                       goto out;
+                       goto out_free;
        }
 
        ret = read;
- out:
+
+out_free:
        trace_parser_put(&parser);
+out_unlock:
        mutex_unlock(&graph_lock);
 
        return ret;
@@ -2583,7 +2626,7 @@ static __init int ftrace_init_dyn_debugfs(struct dentry *d_tracer)
        return 0;
 }
 
-static int ftrace_convert_nops(struct module *mod,
+static int ftrace_process_locs(struct module *mod,
                               unsigned long *start,
                               unsigned long *end)
 {
@@ -2616,19 +2659,17 @@ static int ftrace_convert_nops(struct module *mod,
 }
 
 #ifdef CONFIG_MODULES
-void ftrace_release(void *start, void *end)
+void ftrace_release_mod(struct module *mod)
 {
        struct dyn_ftrace *rec;
        struct ftrace_page *pg;
-       unsigned long s = (unsigned long)start;
-       unsigned long e = (unsigned long)end;
 
-       if (ftrace_disabled || !start || start == end)
+       if (ftrace_disabled)
                return;
 
        mutex_lock(&ftrace_lock);
        do_for_each_ftrace_rec(pg, rec) {
-               if ((rec->ip >= s) && (rec->ip < e)) {
+               if (within_module_core(rec->ip, mod)) {
                        /*
                         * rec->ip is changed in ftrace_free_rec()
                         * It should not between s and e if record was freed.
@@ -2645,7 +2686,7 @@ static void ftrace_init_module(struct module *mod,
 {
        if (ftrace_disabled || start == end)
                return;
-       ftrace_convert_nops(mod, start, end);
+       ftrace_process_locs(mod, start, end);
 }
 
 static int ftrace_module_notify(struct notifier_block *self,
@@ -2660,9 +2701,7 @@ static int ftrace_module_notify(struct notifier_block *self,
                                   mod->num_ftrace_callsites);
                break;
        case MODULE_STATE_GOING:
-               ftrace_release(mod->ftrace_callsites,
-                              mod->ftrace_callsites +
-                              mod->num_ftrace_callsites);
+               ftrace_release_mod(mod);
                break;
        }
 
@@ -2708,7 +2747,7 @@ void __init ftrace_init(void)
 
        last_ftrace_enabled = ftrace_enabled = 1;
 
-       ret = ftrace_convert_nops(NULL,
+       ret = ftrace_process_locs(NULL,
                                  __start_mcount_loc,
                                  __stop_mcount_loc);
 
@@ -2741,23 +2780,6 @@ static inline void ftrace_startup_enable(int command) { }
 # define ftrace_shutdown_sysctl()      do { } while (0)
 #endif /* CONFIG_DYNAMIC_FTRACE */
 
-static ssize_t
-ftrace_pid_read(struct file *file, char __user *ubuf,
-                      size_t cnt, loff_t *ppos)
-{
-       char buf[64];
-       int r;
-
-       if (ftrace_pid_trace == ftrace_swapper_pid)
-               r = sprintf(buf, "swapper tasks\n");
-       else if (ftrace_pid_trace)
-               r = sprintf(buf, "%u\n", pid_vnr(ftrace_pid_trace));
-       else
-               r = sprintf(buf, "no pid\n");
-
-       return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
-}
-
 static void clear_ftrace_swapper(void)
 {
        struct task_struct *p;
@@ -2808,14 +2830,12 @@ static void set_ftrace_pid(struct pid *pid)
        rcu_read_unlock();
 }
 
-static void clear_ftrace_pid_task(struct pid **pid)
+static void clear_ftrace_pid_task(struct pid *pid)
 {
-       if (*pid == ftrace_swapper_pid)
+       if (pid == ftrace_swapper_pid)
                clear_ftrace_swapper();
        else
-               clear_ftrace_pid(*pid);
-
-       *pid = NULL;
+               clear_ftrace_pid(pid);
 }
 
 static void set_ftrace_pid_task(struct pid *pid)
@@ -2826,74 +2846,184 @@ static void set_ftrace_pid_task(struct pid *pid)
                set_ftrace_pid(pid);
 }
 
-static ssize_t
-ftrace_pid_write(struct file *filp, const char __user *ubuf,
-                  size_t cnt, loff_t *ppos)
+static int ftrace_pid_add(int p)
 {
        struct pid *pid;
-       char buf[64];
-       long val;
-       int ret;
+       struct ftrace_pid *fpid;
+       int ret = -EINVAL;
 
-       if (cnt >= sizeof(buf))
-               return -EINVAL;
+       mutex_lock(&ftrace_lock);
 
-       if (copy_from_user(&buf, ubuf, cnt))
-               return -EFAULT;
+       if (!p)
+               pid = ftrace_swapper_pid;
+       else
+               pid = find_get_pid(p);
 
-       buf[cnt] = 0;
+       if (!pid)
+               goto out;
 
-       ret = strict_strtol(buf, 10, &val);
-       if (ret < 0)
-               return ret;
+       ret = 0;
 
-       mutex_lock(&ftrace_lock);
-       if (val < 0) {
-               /* disable pid tracing */
-               if (!ftrace_pid_trace)
-                       goto out;
+       list_for_each_entry(fpid, &ftrace_pids, list)
+               if (fpid->pid == pid)
+                       goto out_put;
 
-               clear_ftrace_pid_task(&ftrace_pid_trace);
+       ret = -ENOMEM;
 
-       } else {
-               /* swapper task is special */
-               if (!val) {
-                       pid = ftrace_swapper_pid;
-                       if (pid == ftrace_pid_trace)
-                               goto out;
-               } else {
-                       pid = find_get_pid(val);
+       fpid = kmalloc(sizeof(*fpid), GFP_KERNEL);
+       if (!fpid)
+               goto out_put;
 
-                       if (pid == ftrace_pid_trace) {
-                               put_pid(pid);
-                               goto out;
-                       }
-               }
+       list_add(&fpid->list, &ftrace_pids);
+       fpid->pid = pid;
 
-               if (ftrace_pid_trace)
-                       clear_ftrace_pid_task(&ftrace_pid_trace);
+       set_ftrace_pid_task(pid);
 
-               if (!pid)
-                       goto out;
+       ftrace_update_pid_func();
+       ftrace_startup_enable(0);
+
+       mutex_unlock(&ftrace_lock);
+       return 0;
 
-               ftrace_pid_trace = pid;
+out_put:
+       if (pid != ftrace_swapper_pid)
+               put_pid(pid);
 
-               set_ftrace_pid_task(ftrace_pid_trace);
+out:
+       mutex_unlock(&ftrace_lock);
+       return ret;
+}
+
+static void ftrace_pid_reset(void)
+{
+       struct ftrace_pid *fpid, *safe;
+
+       mutex_lock(&ftrace_lock);
+       list_for_each_entry_safe(fpid, safe, &ftrace_pids, list) {
+               struct pid *pid = fpid->pid;
+
+               clear_ftrace_pid_task(pid);
+
+               list_del(&fpid->list);
+               kfree(fpid);
        }
 
-       /* update the function call */
        ftrace_update_pid_func();
        ftrace_startup_enable(0);
 
- out:
        mutex_unlock(&ftrace_lock);
+}
 
-       return cnt;
+static void *fpid_start(struct seq_file *m, loff_t *pos)
+{
+       mutex_lock(&ftrace_lock);
+
+       if (list_empty(&ftrace_pids) && (!*pos))
+               return (void *) 1;
+
+       return seq_list_start(&ftrace_pids, *pos);
+}
+
+static void *fpid_next(struct seq_file *m, void *v, loff_t *pos)
+{
+       if (v == (void *)1)
+               return NULL;
+
+       return seq_list_next(v, &ftrace_pids, pos);
+}
+
+static void fpid_stop(struct seq_file *m, void *p)
+{
+       mutex_unlock(&ftrace_lock);
+}
+
+static int fpid_show(struct seq_file *m, void *v)
+{
+       const struct ftrace_pid *fpid = list_entry(v, struct ftrace_pid, list);
+
+       if (v == (void *)1) {
+               seq_printf(m, "no pid\n");
+               return 0;
+       }
+
+       if (fpid->pid == ftrace_swapper_pid)
+               seq_printf(m, "swapper tasks\n");
+       else
+               seq_printf(m, "%u\n", pid_vnr(fpid->pid));
+
+       return 0;
+}
+
+static const struct seq_operations ftrace_pid_sops = {
+       .start = fpid_start,
+       .next = fpid_next,
+       .stop = fpid_stop,
+       .show = fpid_show,
+};
+
+static int
+ftrace_pid_open(struct inode *inode, struct file *file)
+{
+       int ret = 0;
+
+       if ((file->f_mode & FMODE_WRITE) &&
+           (file->f_flags & O_TRUNC))
+               ftrace_pid_reset();
+
+       if (file->f_mode & FMODE_READ)
+               ret = seq_open(file, &ftrace_pid_sops);
+
+       return ret;
+}
+
+static ssize_t
+ftrace_pid_write(struct file *filp, const char __user *ubuf,
+                  size_t cnt, loff_t *ppos)
+{
+       char buf[64], *tmp;
+       long val;
+       int ret;
+
+       if (cnt >= sizeof(buf))
+               return -EINVAL;
+
+       if (copy_from_user(&buf, ubuf, cnt))
+               return -EFAULT;
+
+       buf[cnt] = 0;
+
+       /*
+        * Allow "echo > set_ftrace_pid" or "echo -n '' > set_ftrace_pid"
+        * to clean the filter quietly.
+        */
+       tmp = strstrip(buf);
+       if (strlen(tmp) == 0)
+               return 1;
+
+       ret = strict_strtol(tmp, 10, &val);
+       if (ret < 0)
+               return ret;
+
+       ret = ftrace_pid_add(val);
+
+       return ret ? ret : cnt;
+}
+
+static int
+ftrace_pid_release(struct inode *inode, struct file *file)
+{
+       if (file->f_mode & FMODE_READ)
+               seq_release(inode, file);
+
+       return 0;
 }
 
 static const struct file_operations ftrace_pid_fops = {
-       .read = ftrace_pid_read,
-       .write = ftrace_pid_write,
+       .open           = ftrace_pid_open,
+       .write          = ftrace_pid_write,
+       .read           = seq_read,
+       .llseek         = seq_lseek,
+       .release        = ftrace_pid_release,
 };
 
 static __init int ftrace_init_debugfs(void)
@@ -2976,7 +3106,7 @@ int unregister_ftrace_function(struct ftrace_ops *ops)
 
 int
 ftrace_enable_sysctl(struct ctl_table *table, int write,
-                    struct file *file, void __user *buffer, size_t *lenp,
+                    void __user *buffer, size_t *lenp,
                     loff_t *ppos)
 {
        int ret;
@@ -2986,7 +3116,7 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
 
        mutex_lock(&ftrace_lock);
 
-       ret  = proc_dointvec(table, write, file, buffer, lenp, ppos);
+       ret  = proc_dointvec(table, write, buffer, lenp, ppos);
 
        if (ret || !write || (last_ftrace_enabled == !!ftrace_enabled))
                goto out;
@@ -3256,4 +3386,3 @@ void ftrace_graph_stop(void)
        ftrace_stop();
 }
 #endif
-