1 files changed, 269 insertions, 83 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index e5125677efa0..4f1dade56981 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -39,6 +39,7 @@
 #include <linux/poll.h>
 #include <linux/nmi.h>
 #include <linux/fs.h>
+#include <linux/sched/rt.h>
 
 #include "trace.h"
 #include "trace_output.h"
@@ -249,7 +250,7 @@ static unsigned long		trace_buf_size = TRACE_BUF_SIZE_DEFAULT;
 static struct tracer            *trace_types __read_mostly;
 
 /* current_trace points to the tracer that is currently active */
-static struct tracer            *current_trace __read_mostly;
+static struct tracer            *current_trace __read_mostly = &nop_trace;
 
 /*
  * trace_types_lock is used to protect the trace_types list.
@@ -703,18 +704,22 @@ __update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
 void
 update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
 {
-        struct ring_buffer *buf = tr->buffer;
+        struct ring_buffer *buf;
 
         if (trace_stop_count)
                 return;
 
         WARN_ON_ONCE(!irqs_disabled());
-        if (!current_trace->use_max_tr) {
-                WARN_ON_ONCE(1);
+
+        if (!current_trace->allocated_snapshot) {
+                /* Only the nop tracer should hit this when disabling */
+                WARN_ON_ONCE(current_trace != &nop_trace);
                 return;
         }
+
         arch_spin_lock(&ftrace_max_lock);
 
+        buf = tr->buffer;
         tr->buffer = max_tr.buffer;
         max_tr.buffer = buf;
 
@@ -739,10 +744,8 @@ update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu)
                 return;
 
         WARN_ON_ONCE(!irqs_disabled());
-        if (!current_trace->use_max_tr) {
-                WARN_ON_ONCE(1);
+        if (WARN_ON_ONCE(!current_trace->allocated_snapshot))
                 return;
-        }
 
         arch_spin_lock(&ftrace_max_lock);
 
@@ -862,10 +865,13 @@ int register_tracer(struct tracer *type)
 
                 current_trace = type;
 
-                /* If we expanded the buffers, make sure the max is expanded too */
-                if (ring_buffer_expanded && type->use_max_tr)
-                        ring_buffer_resize(max_tr.buffer, trace_buf_size,
-                                                RING_BUFFER_ALL_CPUS);
+                if (type->use_max_tr) {
+                        /* If we expanded the buffers, make sure the max is expanded too */
+                        if (ring_buffer_expanded)
+                                ring_buffer_resize(max_tr.buffer, trace_buf_size,
+                                                   RING_BUFFER_ALL_CPUS);
+                        type->allocated_snapshot = true;
+                }
 
                 /* the test is responsible for initializing and enabling */
                 pr_info("Testing tracer %s: ", type->name);
@@ -881,10 +887,14 @@ int register_tracer(struct tracer *type)
                 /* Only reset on passing, to avoid touching corrupted buffers */
                 tracing_reset_online_cpus(tr);
 
-                /* Shrink the max buffer again */
-                if (ring_buffer_expanded && type->use_max_tr)
-                        ring_buffer_resize(max_tr.buffer, 1,
-                                                RING_BUFFER_ALL_CPUS);
+                if (type->use_max_tr) {
+                        type->allocated_snapshot = false;
+
+                        /* Shrink the max buffer again */
+                        if (ring_buffer_expanded)
+                                ring_buffer_resize(max_tr.buffer, 1,
+                                                   RING_BUFFER_ALL_CPUS);
+                }
 
                 printk(KERN_CONT "PASSED\n");
         }
@@ -922,6 +932,9 @@ void tracing_reset(struct trace_array *tr, int cpu)
 {
         struct ring_buffer *buffer = tr->buffer;
 
+        if (!buffer)
+                return;
+
         ring_buffer_record_disable(buffer);
 
         /* Make sure all commits have finished */
@@ -936,6 +949,9 @@ void tracing_reset_online_cpus(struct trace_array *tr)
         struct ring_buffer *buffer = tr->buffer;
         int cpu;
 
+        if (!buffer)
+                return;
+
         ring_buffer_record_disable(buffer);
 
         /* Make sure all commits have finished */
@@ -1167,7 +1183,6 @@ tracing_generic_entry_update(struct trace_entry *entry, unsigned long flags,
 
         entry->preempt_count            = pc & 0xff;
         entry->pid                      = (tsk) ? tsk->pid : 0;
-        entry->padding                  = 0;
         entry->flags =
 #ifdef CONFIG_TRACE_IRQFLAGS_SUPPORT
                 (irqs_disabled_flags(flags) ? TRACE_FLAG_IRQS_OFF : 0) |
@@ -1335,7 +1350,7 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer,
          */
         preempt_disable_notrace();
 
-        use_stack = ++__get_cpu_var(ftrace_stack_reserve);
+        use_stack = __this_cpu_inc_return(ftrace_stack_reserve);
         /*
          * We don't need any atomic variables, just a barrier.
          * If an interrupt comes in, we don't care, because it would
@@ -1389,7 +1404,7 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer,
  out:
         /* Again, don't let gcc optimize things here */
         barrier();
-        __get_cpu_var(ftrace_stack_reserve)--;
+        __this_cpu_dec(ftrace_stack_reserve);
         preempt_enable_notrace();
 
 }
@@ -1517,7 +1532,6 @@ static struct trace_buffer_struct *trace_percpu_nmi_buffer;
 static char *get_trace_buf(void)
 {
         struct trace_buffer_struct *percpu_buffer;
-        struct trace_buffer_struct *buffer;
 
         /*
          * If we have allocated per cpu buffers, then we do not
@@ -1535,9 +1549,7 @@ static char *get_trace_buf(void)
         if (!percpu_buffer)
                 return NULL;
 
-        buffer = per_cpu_ptr(percpu_buffer, smp_processor_id());
-
-        return buffer->buffer;
+        return this_cpu_ptr(&percpu_buffer->buffer[0]);
 }
 
 static int alloc_percpu_trace_buffer(void)
@@ -1942,21 +1954,27 @@ void tracing_iter_reset(struct trace_iterator *iter, int cpu)
 static void *s_start(struct seq_file *m, loff_t *pos)
 {
         struct trace_iterator *iter = m->private;
-        static struct tracer *old_tracer;
         int cpu_file = iter->cpu_file;
         void *p = NULL;
         loff_t l = 0;
         int cpu;
 
-        /* copy the tracer to avoid using a global lock all around */
+        /*
+         * copy the tracer to avoid using a global lock all around.
+         * iter->trace is a copy of current_trace, the pointer to the
+         * name may be used instead of a strcmp(), as iter->trace->name
+         * will point to the same string as current_trace->name.
+         */
         mutex_lock(&trace_types_lock);
-        if (unlikely(old_tracer != current_trace && current_trace)) {
-                old_tracer = current_trace;
+        if (unlikely(current_trace && iter->trace->name != current_trace->name))
                 *iter->trace = *current_trace;
-        }
         mutex_unlock(&trace_types_lock);
 
-        atomic_inc(&trace_record_cmdline_disabled);
+        if (iter->snapshot && iter->trace->use_max_tr)
+                return ERR_PTR(-EBUSY);
+
+        if (!iter->snapshot)
+                atomic_inc(&trace_record_cmdline_disabled);
 
         if (*pos != iter->pos) {
                 iter->ent = NULL;
@@ -1995,7 +2013,11 @@ static void s_stop(struct seq_file *m, void *p)
 {
         struct trace_iterator *iter = m->private;
 
-        atomic_dec(&trace_record_cmdline_disabled);
+        if (iter->snapshot && iter->trace->use_max_tr)
+                return;
+
+        if (!iter->snapshot)
+                atomic_dec(&trace_record_cmdline_disabled);
         trace_access_unlock(iter->cpu_file);
         trace_event_read_unlock();
 }
@@ -2080,8 +2102,7 @@ print_trace_header(struct seq_file *m, struct trace_iterator *iter)
         unsigned long total;
         const char *name = "preemption";
 
-        if (type)
-                name = type->name;
+        name = type->name;
 
         get_total_entries(tr, &total, &entries);
 
@@ -2380,6 +2401,27 @@ static void test_ftrace_alive(struct seq_file *m)
         seq_printf(m, "#          MAY BE MISSING FUNCTION EVENTS\n");
 }
 
+#ifdef CONFIG_TRACER_MAX_TRACE
+static void print_snapshot_help(struct seq_file *m, struct trace_iterator *iter)
+{
+        if (iter->trace->allocated_snapshot)
+                seq_printf(m, "#\n# * Snapshot is allocated *\n#\n");
+        else
+                seq_printf(m, "#\n# * Snapshot is freed *\n#\n");
+
+        seq_printf(m, "# Snapshot commands:\n");
+        seq_printf(m, "# echo 0 > snapshot : Clears and frees snapshot buffer\n");
+        seq_printf(m, "# echo 1 > snapshot : Allocates snapshot buffer, if not already allocated.\n");
+        seq_printf(m, "#                      Takes a snapshot of the main buffer.\n");
+        seq_printf(m, "# echo 2 > snapshot : Clears snapshot buffer (but does not allocate)\n");
+        seq_printf(m, "#                      (Doesn't have to be '2' works with any number that\n");
+        seq_printf(m, "#                       is not a '0' or '1')\n");
+}
+#else
+/* Should never be called */
+static inline void print_snapshot_help(struct seq_file *m, struct trace_iterator *iter) { }
+#endif
+
 static int s_show(struct seq_file *m, void *v)
 {
         struct trace_iterator *iter = v;
@@ -2391,7 +2433,9 @@ static int s_show(struct seq_file *m, void *v)
                         seq_puts(m, "#\n");
                         test_ftrace_alive(m);
                 }
-                if (iter->trace && iter->trace->print_header)
+                if (iter->snapshot && trace_empty(iter))
+                        print_snapshot_help(m, iter);
+                else if (iter->trace && iter->trace->print_header)
                         iter->trace->print_header(m);
                 else
                         trace_default_header(m);
@@ -2430,7 +2474,7 @@ static const struct seq_operations tracer_seq_ops = {
 };
 
 static struct trace_iterator *
-__tracing_open(struct inode *inode, struct file *file)
+__tracing_open(struct inode *inode, struct file *file, bool snapshot)
 {
         long cpu_file = (long) inode->i_private;
         struct trace_iterator *iter;
@@ -2457,16 +2501,16 @@ __tracing_open(struct inode *inode, struct file *file)
         if (!iter->trace)
                 goto fail;
 
-        if (current_trace)
-                *iter->trace = *current_trace;
+        *iter->trace = *current_trace;
 
         if (!zalloc_cpumask_var(&iter->started, GFP_KERNEL))
                 goto fail;
 
-        if (current_trace && current_trace->print_max)
+        if (current_trace->print_max || snapshot)
                 iter->tr = &max_tr;
         else
                 iter->tr = &global_trace;
+        iter->snapshot = snapshot;
         iter->pos = -1;
         mutex_init(&iter->mutex);
         iter->cpu_file = cpu_file;
@@ -2483,8 +2527,9 @@ __tracing_open(struct inode *inode, struct file *file)
         if (trace_clocks[trace_clock_id].in_ns)
                 iter->iter_flags |= TRACE_FILE_TIME_IN_NS;
 
-        /* stop the trace while dumping */
-        tracing_stop();
+        /* stop the trace while dumping if we are not opening "snapshot" */
+        if (!iter->snapshot)
+                tracing_stop();
 
         if (iter->cpu_file == TRACE_PIPE_ALL_CPU) {
                 for_each_tracing_cpu(cpu) {
@@ -2547,8 +2592,9 @@ static int tracing_release(struct inode *inode, struct file *file)
         if (iter->trace && iter->trace->close)
                 iter->trace->close(iter);
 
-        /* reenable tracing if it was previously enabled */
-        tracing_start();
+        if (!iter->snapshot)
+                /* reenable tracing if it was previously enabled */
+                tracing_start();
         mutex_unlock(&trace_types_lock);
 
         mutex_destroy(&iter->mutex);
@@ -2576,7 +2622,7 @@ static int tracing_open(struct inode *inode, struct file *file)
         }
 
         if (file->f_mode & FMODE_READ) {
-                iter = __tracing_open(inode, file);
+                iter = __tracing_open(inode, file, false);
                 if (IS_ERR(iter))
                         ret = PTR_ERR(iter);
                 else if (trace_flags & TRACE_ITER_LATENCY_FMT)
@@ -2835,11 +2881,25 @@ static int set_tracer_option(struct tracer *trace, char *cmp, int neg)
         return -EINVAL;
 }
 
-static void set_tracer_flags(unsigned int mask, int enabled)
+/* Some tracers require overwrite to stay enabled */
+int trace_keep_overwrite(struct tracer *tracer, u32 mask, int set)
+{
+        if (tracer->enabled && (mask & TRACE_ITER_OVERWRITE) && !set)
+                return -1;
+
+        return 0;
+}
+
+int set_tracer_flag(unsigned int mask, int enabled)
 {
         /* do nothing if flag is already set */
         if (!!(trace_flags & mask) == !!enabled)
-                return;
+                return 0;
+
+        /* Give the tracer a chance to approve the change */
+        if (current_trace->flag_changed)
+                if (current_trace->flag_changed(current_trace, mask, !!enabled))
+                        return -EINVAL;
 
         if (enabled)
                 trace_flags |= mask;
@@ -2849,18 +2909,24 @@ static void set_tracer_flags(unsigned int mask, int enabled)
         if (mask == TRACE_ITER_RECORD_CMD)
                 trace_event_enable_cmd_record(enabled);
 
-        if (mask == TRACE_ITER_OVERWRITE)
+        if (mask == TRACE_ITER_OVERWRITE) {
                 ring_buffer_change_overwrite(global_trace.buffer, enabled);
+#ifdef CONFIG_TRACER_MAX_TRACE
+                ring_buffer_change_overwrite(max_tr.buffer, enabled);
+#endif
+        }
 
         if (mask == TRACE_ITER_PRINTK)
                 trace_printk_start_stop_comm(enabled);
+
+        return 0;
 }
 
 static int trace_set_options(char *option)
 {
         char *cmp;
         int neg = 0;
-        int ret = 0;
+        int ret = -ENODEV;
         int i;
 
         cmp = strstrip(option);
@@ -2870,19 +2936,20 @@ static int trace_set_options(char *option)
                 cmp += 2;
         }
 
+        mutex_lock(&trace_types_lock);
+
         for (i = 0; trace_options[i]; i++) {
                 if (strcmp(cmp, trace_options[i]) == 0) {
-                        set_tracer_flags(1 << i, !neg);
+                        ret = set_tracer_flag(1 << i, !neg);
                         break;
                 }
         }
 
         /* If no option could be set, test the specific tracer options */
-        if (!trace_options[i]) {
-                mutex_lock(&trace_types_lock);
+        if (!trace_options[i])
                 ret = set_tracer_option(current_trace, cmp, neg);
-                mutex_unlock(&trace_types_lock);
-        }
+
+        mutex_unlock(&trace_types_lock);
 
         return ret;
 }
@@ -2892,6 +2959,7 @@ tracing_trace_options_write(struct file *filp, const char __user *ubuf,
                         size_t cnt, loff_t *ppos)
 {
         char buf[64];
+        int ret;
 
         if (cnt >= sizeof(buf))
                 return -EINVAL;
@@ -2899,7 +2967,11 @@ tracing_trace_options_write(struct file *filp, const char __user *ubuf,
         if (copy_from_user(&buf, ubuf, cnt))
                 return -EFAULT;
 
-        trace_set_options(buf);
+        buf[cnt] = 0;
+
+        ret = trace_set_options(buf);
+        if (ret < 0)
+                return ret;
 
         *ppos += cnt;
 
@@ -3012,10 +3084,7 @@ tracing_set_trace_read(struct file *filp, char __user *ubuf,
         int r;
 
         mutex_lock(&trace_types_lock);
-        if (current_trace)
-                r = sprintf(buf, "%s\n", current_trace->name);
-        else
-                r = sprintf(buf, "\n");
+        r = sprintf(buf, "%s\n", current_trace->name);
         mutex_unlock(&trace_types_lock);
 
         return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
@@ -3181,6 +3250,7 @@ static int tracing_set_tracer(const char *buf)
         static struct trace_option_dentry *topts;
         struct trace_array *tr = &global_trace;
         struct tracer *t;
+        bool had_max_tr;
         int ret = 0;
 
         mutex_lock(&trace_types_lock);
@@ -3205,9 +3275,24 @@ static int tracing_set_tracer(const char *buf)
                 goto out;
 
         trace_branch_disable();
-        if (current_trace && current_trace->reset)
+
+        current_trace->enabled = false;
+
+        if (current_trace->reset)
                 current_trace->reset(tr);
-        if (current_trace && current_trace->use_max_tr) {
+
+        had_max_tr = current_trace->allocated_snapshot;
+        current_trace = &nop_trace;
+
+        if (had_max_tr && !t->use_max_tr) {
+                /*
+                 * We need to make sure that the update_max_tr sees that
+                 * current_trace changed to nop_trace to keep it from
+                 * swapping the buffers after we resize it.
+                 * The update_max_tr is called from interrupts disabled
+                 * so a synchronized_sched() is sufficient.
+                 */
+                synchronize_sched();
                 /*
                  * We don't free the ring buffer. instead, resize it because
                  * The max_tr ring buffer has some state (e.g. ring->clock) and
@@ -3215,18 +3300,19 @@ static int tracing_set_tracer(const char *buf)
                  */
                 ring_buffer_resize(max_tr.buffer, 1, RING_BUFFER_ALL_CPUS);
                 set_buffer_entries(&max_tr, 1);
+                tracing_reset_online_cpus(&max_tr);
+                current_trace->allocated_snapshot = false;
         }
         destroy_trace_option_files(topts);
 
-        current_trace = &nop_trace;
-
         topts = create_trace_option_files(t);
-        if (t->use_max_tr) {
+        if (t->use_max_tr && !had_max_tr) {
                 /* we need to make per cpu buffer sizes equivalent */
                 ret = resize_buffer_duplicate_size(&max_tr, &global_trace,
                                                    RING_BUFFER_ALL_CPUS);
                 if (ret < 0)
                         goto out;
+                t->allocated_snapshot = true;
         }
 
         if (t->init) {
@@ -3236,6 +3322,7 @@ static int tracing_set_tracer(const char *buf)
         }
 
         current_trace = t;
+        current_trace->enabled = true;
         trace_branch_enable(tr);
  out:
         mutex_unlock(&trace_types_lock);
@@ -3334,8 +3421,7 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
                 ret = -ENOMEM;
                 goto fail;
         }
-        if (current_trace)
-                *iter->trace = *current_trace;
+        *iter->trace = *current_trace;
 
         if (!alloc_cpumask_var(&iter->started, GFP_KERNEL)) {
                 ret = -ENOMEM;
@@ -3452,7 +3538,7 @@ static int tracing_wait_pipe(struct file *filp)
                         return -EINTR;
 
                 /*
-                 * We block until we read something and tracing is enabled.
+                 * We block until we read something and tracing is disabled.
                  * We still block if tracing is disabled, but we have never
                  * read anything. This allows a user to cat this file, and
                  * then enable tracing. But after we have read something,
@@ -3460,7 +3546,7 @@ static int tracing_wait_pipe(struct file *filp)
                  *
                  * iter->pos will be 0 if we haven't read anything.
                  */
-                if (tracing_is_enabled() && iter->pos)
+                if (!tracing_is_enabled() && iter->pos)
                         break;
         }
 
@@ -3475,7 +3561,6 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
                   size_t cnt, loff_t *ppos)
 {
         struct trace_iterator *iter = filp->private_data;
-        static struct tracer *old_tracer;
         ssize_t sret;
 
         /* return any leftover data */
@@ -3487,10 +3572,8 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 
         /* copy the tracer to avoid using a global lock all around */
         mutex_lock(&trace_types_lock);
-        if (unlikely(old_tracer != current_trace && current_trace)) {
-                old_tracer = current_trace;
+        if (unlikely(iter->trace->name != current_trace->name))
                 *iter->trace = *current_trace;
-        }
         mutex_unlock(&trace_types_lock);
 
         /*
@@ -3646,7 +3729,6 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
                 .ops            = &tracing_pipe_buf_ops,
                 .spd_release    = tracing_spd_release_pipe,
         };
-        static struct tracer *old_tracer;
         ssize_t ret;
         size_t rem;
         unsigned int i;
@@ -3656,10 +3738,8 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 
         /* copy the tracer to avoid using a global lock all around */
         mutex_lock(&trace_types_lock);
-        if (unlikely(old_tracer != current_trace && current_trace)) {
-                old_tracer = current_trace;
+        if (unlikely(iter->trace->name != current_trace->name))
                 *iter->trace = *current_trace;
-        }
         mutex_unlock(&trace_types_lock);
 
         mutex_lock(&iter->mutex);
@@ -4035,8 +4115,7 @@ static ssize_t tracing_clock_write(struct file *filp, const char __user *ubuf,
          * Reset the buffer so that it doesn't have incomparable timestamps.
          */
         tracing_reset_online_cpus(&global_trace);
-        if (max_tr.buffer)
-                tracing_reset_online_cpus(&max_tr);
+        tracing_reset_online_cpus(&max_tr);
 
         mutex_unlock(&trace_types_lock);
 
@@ -4052,6 +4131,85 @@ static int tracing_clock_open(struct inode *inode, struct file *file)
         return single_open(file, tracing_clock_show, NULL);
 }
 
+#ifdef CONFIG_TRACER_SNAPSHOT
+static int tracing_snapshot_open(struct inode *inode, struct file *file)
+{
+        struct trace_iterator *iter;
+        int ret = 0;
+
+        if (file->f_mode & FMODE_READ) {
+                iter = __tracing_open(inode, file, true);
+                if (IS_ERR(iter))
+                        ret = PTR_ERR(iter);
+        }
+        return ret;
+}
+
+static ssize_t
+tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
+                       loff_t *ppos)
+{
+        unsigned long val;
+        int ret;
+
+        ret = tracing_update_buffers();
+        if (ret < 0)
+                return ret;
+
+        ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
+        if (ret)
+                return ret;
+
+        mutex_lock(&trace_types_lock);
+
+        if (current_trace->use_max_tr) {
+                ret = -EBUSY;
+                goto out;
+        }
+
+        switch (val) {
+        case 0:
+                if (current_trace->allocated_snapshot) {
+                        /* free spare buffer */
+                        ring_buffer_resize(max_tr.buffer, 1,
+                                           RING_BUFFER_ALL_CPUS);
+                        set_buffer_entries(&max_tr, 1);
+                        tracing_reset_online_cpus(&max_tr);
+                        current_trace->allocated_snapshot = false;
+                }
+                break;
+        case 1:
+                if (!current_trace->allocated_snapshot) {
+                        /* allocate spare buffer */
+                        ret = resize_buffer_duplicate_size(&max_tr,
+                                        &global_trace, RING_BUFFER_ALL_CPUS);
+                        if (ret < 0)
+                                break;
+                        current_trace->allocated_snapshot = true;
+                }
+
+                local_irq_disable();
+                /* Now, we're going to swap */
+                update_max_tr(&global_trace, current, smp_processor_id());
+                local_irq_enable();
+                break;
+        default:
+                if (current_trace->allocated_snapshot)
+                        tracing_reset_online_cpus(&max_tr);
+                break;
+        }
+
+        if (ret >= 0) {
+                *ppos += cnt;
+                ret = cnt;
+        }
+out:
+        mutex_unlock(&trace_types_lock);
+        return ret;
+}
+#endif /* CONFIG_TRACER_SNAPSHOT */
+
+
 static const struct file_operations tracing_max_lat_fops = {
         .open           = tracing_open_generic,
         .read           = tracing_max_lat_read,
@@ -4108,6 +4266,16 @@ static const struct file_operations trace_clock_fops = {
         .write          = tracing_clock_write,
 };
 
+#ifdef CONFIG_TRACER_SNAPSHOT
+static const struct file_operations snapshot_fops = {
+        .open           = tracing_snapshot_open,
+        .read           = seq_read,
+        .write          = tracing_snapshot_write,
+        .llseek         = tracing_seek,
+        .release        = tracing_release,
+};
+#endif /* CONFIG_TRACER_SNAPSHOT */
+
 struct ftrace_buffer_info {
         struct trace_array      *tr;
         void                    *spare;
@@ -4412,6 +4580,9 @@ tracing_stats_read(struct file *filp, char __user *ubuf,
         cnt = ring_buffer_dropped_events_cpu(tr->buffer, cpu);
         trace_seq_printf(s, "dropped events: %ld\n", cnt);
 
+        cnt = ring_buffer_read_events_cpu(tr->buffer, cpu);
+        trace_seq_printf(s, "read events: %ld\n", cnt);
+
         count = simple_read_from_buffer(ubuf, count, ppos, s->buffer, s->len);
 
         kfree(s);
@@ -4488,7 +4659,7 @@ struct dentry *tracing_init_dentry(void)
 
 static struct dentry *d_percpu;
 
-struct dentry *tracing_dentry_percpu(void)
+static struct dentry *tracing_dentry_percpu(void)
 {
         static int once;
         struct dentry *d_tracer;
@@ -4638,7 +4809,13 @@ trace_options_core_write(struct file *filp, const char __user *ubuf, size_t cnt,
 
         if (val != 0 && val != 1)
                 return -EINVAL;
-        set_tracer_flags(1 << index, val);
+
+        mutex_lock(&trace_types_lock);
+        ret = set_tracer_flag(1 << index, val);
+        mutex_unlock(&trace_types_lock);
+
+        if (ret < 0)
+                return ret;
 
         *ppos += cnt;
 
@@ -4815,10 +4992,17 @@ rb_simple_write(struct file *filp, const char __user *ubuf,
                 return ret;
 
         if (buffer) {
-                if (val)
+                mutex_lock(&trace_types_lock);
+                if (val) {
                         ring_buffer_record_on(buffer);
-                else
+                        if (current_trace->start)
+                                current_trace->start(tr);
+                } else {
                         ring_buffer_record_off(buffer);
+                        if (current_trace->stop)
+                                current_trace->stop(tr);
+                }
+                mutex_unlock(&trace_types_lock);
         }
 
         (*ppos)++;
@@ -4897,6 +5081,11 @@ static __init int tracer_init_debugfs(void)
                         &ftrace_update_tot_cnt, &tracing_dyn_info_fops);
 #endif
 
+#ifdef CONFIG_TRACER_SNAPSHOT
+        trace_create_file("snapshot", 0644, d_tracer,
+                          (void *) TRACE_PIPE_ALL_CPU, &snapshot_fops);
+#endif
+
         create_trace_options_dir();
 
         for_each_tracing_cpu(cpu)
@@ -5005,6 +5194,7 @@ __ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode)
         if (disable_tracing)
                 ftrace_kill();
 
+        /* Simulate the iterator */
         trace_init_global_iter(&iter);
 
         for_each_tracing_cpu(cpu) {
@@ -5016,10 +5206,6 @@ __ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode)
         /* don't look at user memory in panic mode */
         trace_flags &= ~TRACE_ITER_SYM_USEROBJ;
 
-        /* Simulate the iterator */
-        iter.tr = &global_trace;
-        iter.trace = current_trace;
-
         switch (oops_dump_mode) {
         case DUMP_ALL:
                 iter.cpu_file = TRACE_PIPE_ALL_CPU;
@@ -5164,7 +5350,7 @@ __init static int tracer_alloc_buffers(void)
         init_irq_work(&trace_work_wakeup, trace_wake_up);
 
         register_tracer(&nop_trace);
-        current_trace = &nop_trace;
+
         /* All seems OK, enable tracing */
         tracing_disabled = 0;