1 files changed, 173 insertions, 3 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index cedf4e26828..668bbb5ef2b 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -16,14 +16,49 @@
 #include <linux/list.h>
 #include <linux/fs.h>
 
+#include "trace.h"
+
+/* Global flag to disable all recording to ring buffers */
+static int ring_buffers_off __read_mostly;
+
+/**
+ * tracing_on - enable all tracing buffers
+ *
+ * This function enables all tracing buffers that may have been
+ * disabled with tracing_off.
+ */
+void tracing_on(void)
+{
+        ring_buffers_off = 0;
+}
+
+/**
+ * tracing_off - turn off all tracing buffers
+ *
+ * This function stops all tracing buffers from recording data.
+ * It does not disable any overhead the tracers themselves may
+ * be causing. This function simply causes all recording to
+ * the ring buffers to fail.
+ */
+void tracing_off(void)
+{
+        ring_buffers_off = 1;
+}
+
 /* Up this if you want to test the TIME_EXTENTS and normalization */
 #define DEBUG_SHIFT 0
 
 /* FIXME!!! */
 u64 ring_buffer_time_stamp(int cpu)
 {
+        u64 time;
+
+        preempt_disable_notrace();
         /* shift to debug/test normalization and TIME_EXTENTS */
-        return sched_clock() << DEBUG_SHIFT;
+        time = sched_clock() << DEBUG_SHIFT;
+        preempt_enable_notrace();
+
+        return time;
 }
 
 void ring_buffer_normalize_time_stamp(int cpu, u64 *ts)
@@ -503,6 +538,12 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
         LIST_HEAD(pages);
         int i, cpu;
 
+        /*
+         * Always succeed at resizing a non-existent buffer:
+         */
+        if (!buffer)
+                return size;
+
         size = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
         size *= BUF_PAGE_SIZE;
         buffer_size = buffer->pages * BUF_PAGE_SIZE;
@@ -576,6 +617,7 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
                 list_del_init(&page->list);
                 free_buffer_page(page);
         }
+        mutex_unlock(&buffer->mutex);
         return -ENOMEM;
 }
 
@@ -1022,8 +1064,23 @@ rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
         struct ring_buffer_event *event;
         u64 ts, delta;
         int commit = 0;
+        int nr_loops = 0;
 
  again:
+        /*
+         * We allow for interrupts to reenter here and do a trace.
+         * If one does, it will cause this original code to loop
+         * back here. Even with heavy interrupts happening, this
+         * should only happen a few times in a row. If this happens
+         * 1000 times in a row, there must be either an interrupt
+         * storm or we have something buggy.
+         * Bail!
+         */
+        if (unlikely(++nr_loops > 1000)) {
+                RB_WARN_ON(cpu_buffer, 1);
+                return NULL;
+        }
+
         ts = ring_buffer_time_stamp(cpu_buffer->cpu);
 
         /*
@@ -1045,7 +1102,7 @@ rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
 
                 /* Did the write stamp get updated already? */
                 if (unlikely(ts < cpu_buffer->write_stamp))
-                        goto again;
+                        delta = 0;
 
                 if (test_time_stamp(delta)) {
 
@@ -1118,6 +1175,9 @@ ring_buffer_lock_reserve(struct ring_buffer *buffer,
         struct ring_buffer_event *event;
         int cpu, resched;
 
+        if (ring_buffers_off)
+                return NULL;
+
         if (atomic_read(&buffer->record_disabled))
                 return NULL;
 
@@ -1155,7 +1215,7 @@ ring_buffer_lock_reserve(struct ring_buffer *buffer,
 
  out:
         if (resched)
-                preempt_enable_notrace();
+                preempt_enable_no_resched_notrace();
         else
                 preempt_enable_notrace();
         return NULL;
@@ -1234,6 +1294,9 @@ int ring_buffer_write(struct ring_buffer *buffer,
         int ret = -EBUSY;
         int cpu, resched;
 
+        if (ring_buffers_off)
+                return -EBUSY;
+
         if (atomic_read(&buffer->record_disabled))
                 return -EBUSY;
 
@@ -1532,10 +1595,23 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
 {
         struct buffer_page *reader = NULL;
         unsigned long flags;
+        int nr_loops = 0;
 
         spin_lock_irqsave(&cpu_buffer->lock, flags);
 
  again:
+        /*
+         * This should normally only loop twice. But because the
+         * start of the reader inserts an empty page, it causes
+         * a case where we will loop three times. There should be no
+         * reason to loop four times (that I know of).
+         */
+        if (unlikely(++nr_loops > 3)) {
+                RB_WARN_ON(cpu_buffer, 1);
+                reader = NULL;
+                goto out;
+        }
+
         reader = cpu_buffer->reader_page;
 
         /* If there's more to read, return this page */
@@ -1665,6 +1741,7 @@ ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
         struct ring_buffer_per_cpu *cpu_buffer;
         struct ring_buffer_event *event;
         struct buffer_page *reader;
+        int nr_loops = 0;
 
         if (!cpu_isset(cpu, buffer->cpumask))
                 return NULL;
@@ -1672,6 +1749,19 @@ ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
         cpu_buffer = buffer->buffers[cpu];
 
  again:
+        /*
+         * We repeat when a timestamp is encountered. It is possible
+         * to get multiple timestamps from an interrupt entering just
+         * as one timestamp is about to be written. The max times
+         * that this can happen is the number of nested interrupts we
+         * can have.  Nesting 10 deep of interrupts is clearly
+         * an anomaly.
+         */
+        if (unlikely(++nr_loops > 10)) {
+                RB_WARN_ON(cpu_buffer, 1);
+                return NULL;
+        }
+
         reader = rb_get_reader_page(cpu_buffer);
         if (!reader)
                 return NULL;
@@ -1722,6 +1812,7 @@ ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
         struct ring_buffer *buffer;
         struct ring_buffer_per_cpu *cpu_buffer;
         struct ring_buffer_event *event;
+        int nr_loops = 0;
 
         if (ring_buffer_iter_empty(iter))
                 return NULL;
@@ -1730,6 +1821,19 @@ ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
         buffer = cpu_buffer->buffer;
 
  again:
+        /*
+         * We repeat when a timestamp is encountered. It is possible
+         * to get multiple timestamps from an interrupt entering just
+         * as one timestamp is about to be written. The max times
+         * that this can happen is the number of nested interrupts we
+         * can have. Nesting 10 deep of interrupts is clearly
+         * an anomaly.
+         */
+        if (unlikely(++nr_loops > 10)) {
+                RB_WARN_ON(cpu_buffer, 1);
+                return NULL;
+        }
+
         if (rb_per_cpu_empty(cpu_buffer))
                 return NULL;
 
@@ -2014,3 +2118,69 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
         return 0;
 }
 
+static ssize_t
+rb_simple_read(struct file *filp, char __user *ubuf,
+               size_t cnt, loff_t *ppos)
+{
+        int *p = filp->private_data;
+        char buf[64];
+        int r;
+
+        /* !ring_buffers_off == tracing_on */
+        r = sprintf(buf, "%d\n", !*p);
+
+        return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
+}
+
+static ssize_t
+rb_simple_write(struct file *filp, const char __user *ubuf,
+                size_t cnt, loff_t *ppos)
+{
+        int *p = filp->private_data;
+        char buf[64];
+        long val;
+        int ret;
+
+        if (cnt >= sizeof(buf))
+                return -EINVAL;
+
+        if (copy_from_user(&buf, ubuf, cnt))
+                return -EFAULT;
+
+        buf[cnt] = 0;
+
+        ret = strict_strtoul(buf, 10, &val);
+        if (ret < 0)
+                return ret;
+
+        /* !ring_buffers_off == tracing_on */
+        *p = !val;
+
+        (*ppos)++;
+
+        return cnt;
+}
+
+static struct file_operations rb_simple_fops = {
+        .open           = tracing_open_generic,
+        .read           = rb_simple_read,
+        .write          = rb_simple_write,
+};
+
+
+static __init int rb_init_debugfs(void)
+{
+        struct dentry *d_tracer;
+        struct dentry *entry;
+
+        d_tracer = tracing_init_dentry();
+
+        entry = debugfs_create_file("tracing_on", 0644, d_tracer,
+                                    &ring_buffers_off, &rb_simple_fops);
+        if (!entry)
+                pr_warning("Could not create debugfs 'tracing_on' entry\n");
+
+        return 0;
+}
+
+fs_initcall(rb_init_debugfs);