ftrace: disable tracing on resize

Impact: fix for bug on resize

This patch addresses the bug found here:

 http://bugzilla.kernel.org/show_bug.cgi?id=11996

When ftrace converted to the new unified trace buffer, the resizing of
the buffer was not protected as much as it was originally. If tracing
is performed while the resize occurs, then the buffer can be corrupted.

This patch disables all ftrace buffer modifications before a resize
takes place.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 9f3b478f91716bdd1cc48ac6872c2a3c1412dbb8..abfa8103d04673c66e9dc10d468ba1d6fe8f6b00 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2676,7 +2676,7 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
 {
        unsigned long val;
        char buf[64];
-       int ret;
+       int ret, cpu;
        struct trace_array *tr = filp->private_data;
 
        if (cnt >= sizeof(buf))
@@ -2704,6 +2704,14 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
                goto out;
        }
 
+       /* disable all cpu buffers */
+       for_each_tracing_cpu(cpu) {
+               if (global_trace.data[cpu])
+                       atomic_inc(&global_trace.data[cpu]->disabled);
+               if (max_tr.data[cpu])
+                       atomic_inc(&max_tr.data[cpu]->disabled);
+       }
+
        if (val != global_trace.entries) {
                ret = ring_buffer_resize(global_trace.buffer, val);
                if (ret < 0) {
@@ -2735,6 +2743,13 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
        if (tracing_disabled)
                cnt = -ENOMEM;
  out:
+       for_each_tracing_cpu(cpu) {
+               if (global_trace.data[cpu])
+                       atomic_dec(&global_trace.data[cpu]->disabled);
+               if (max_tr.data[cpu])
+                       atomic_dec(&max_tr.data[cpu]->disabled);
+       }
+
        max_tr.entries = global_trace.entries;
        mutex_unlock(&trace_types_lock);