tracing: Make a snapshot feature available from userspace

Ftrace has a snapshot feature available from kernel space and
latency tracers (e.g. irqsoff) are using it. This patch enables
user applictions to take a snapshot via debugfs.

Add "snapshot" debugfs file in "tracing" directory.

  snapshot:
    This is used to take a snapshot and to read the output of the
    snapshot.

     # echo 1 > snapshot

    This will allocate the spare buffer for snapshot (if it is
    not allocated), and take a snapshot.

     # cat snapshot

    This will show contents of the snapshot.

     # echo 0 > snapshot

    This will free the snapshot if it is allocated.

    Any other positive values will clear the snapshot contents if
    the snapshot is allocated, or return EINVAL if it is not allocated.

Link: http://lkml.kernel.org/r/20121226025300.3252.86850.stgit@liselsia
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: David Sharp <dhsharp@google.com>
Signed-off-by: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
[
   Fixed irqsoff selftest and also a conflict with a change
   that fixes the update_max_tr.
]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 6f8d0b77006b203df54d4afeb488a6a2df67c522..13a54d0bdfa8afbe2cc29ec6bf8ce016c1b2306c 100644 (file)
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -83,6 +83,9 @@ struct trace_iterator {
        long                    idx;
 
        cpumask_var_t           started;
+
+       /* it's true when current open file is snapshot */
+       bool                    snapshot;
 };
 
 enum trace_iter_flags {

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index cdc9d284d24e6378e6270df27bf2f75a8ea20341..36567564e221195d1a8489207fed82f27c36b85e 100644 (file)
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -253,6 +253,16 @@ config FTRACE_SYSCALLS
        help
          Basic tracer to catch the syscall entry and exit events.
 
+config TRACER_SNAPSHOT
+       bool "Create a snapshot trace buffer"
+       select TRACER_MAX_TRACE
+       help
+         Allow tracing users to take snapshot of the current buffer using the
+         ftrace interface, e.g.:
+
+             echo 1 > /sys/kernel/debug/tracing/snapshot
+             cat snapshot
+
 config TRACE_BRANCH_PROFILING
        bool
        select GENERIC_TRACER

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2c724662a3e885071fc4ab442bd3cd1cebf4c217..70dce64b9ecf12f8f99d605cecf62a8016952059 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -710,12 +710,11 @@ update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
 
        WARN_ON_ONCE(!irqs_disabled());
 
-       /* If we disabled the tracer, stop now */
-       if (current_trace == &nop_trace)
-               return;
-
-       if (WARN_ON_ONCE(!current_trace->use_max_tr))
+       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);
 
@@ -743,10 +742,8 @@ 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);
 
@@ -866,10 +863,13 @@ 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);
@@ -885,10 +885,14 @@ 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");
        }
@@ -1964,7 +1968,11 @@ static void *s_start(struct seq_file *m, loff_t *pos)
                *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;
@@ -2003,7 +2011,11 @@ 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();
 }
@@ -2438,7 +2450,7 @@ 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;
@@ -2471,10 +2483,11 @@ __tracing_open(struct inode *inode, struct file *file)
        if (!zalloc_cpumask_var(&iter->started, GFP_KERNEL))
                goto fail;
 
-       if (current_trace && current_trace->print_max)
+       if ((current_trace && 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;
@@ -2491,8 +2504,9 @@ __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) {
@@ -2555,8 +2569,9 @@ 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);
@@ -2584,7 +2599,7 @@ 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)
@@ -3219,7 +3234,7 @@ static int tracing_set_tracer(const char *buf)
        if (current_trace && current_trace->reset)
                current_trace->reset(tr);
 
-       had_max_tr = current_trace && current_trace->use_max_tr;
+       had_max_tr = current_trace && current_trace->allocated_snapshot;
        current_trace = &nop_trace;
 
        if (had_max_tr && !t->use_max_tr) {
@@ -3238,6 +3253,8 @@ 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);
 
@@ -3248,6 +3265,7 @@ static int tracing_set_tracer(const char *buf)
                                                   RING_BUFFER_ALL_CPUS);
                if (ret < 0)
                        goto out;
+               t->allocated_snapshot = true;
        }
 
        if (t->init) {
@@ -4066,6 +4084,87 @@ 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 && 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);
+               else
+                       ret = -EINVAL;
+               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,
@@ -4122,6 +4221,16 @@ 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;
@@ -4921,6 +5030,11 @@ 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)

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 04a2c7ab1735b583bd3cf0c0bc1cfe581a611cb6..57d7e5397d56da86f667e3139fb14703a99e8fcf 100644 (file)
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -287,6 +287,7 @@ struct tracer {
        struct tracer_flags     *flags;
        bool                    print_max;
        bool                    use_max_tr;
+       bool                    allocated_snapshot;
 };