[PATCH 08/14] ring-buffer: Make sure the spare sub buffer used for reads has same size

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rost...@goodmis.org>

Now that the ring buffer specifies the size of its sub buffers, they all
need to be the same size. When doing a read, a swap is done with a spare
page. Make sure they are the same size before doing the swap, otherwise
the read will fail.

Signed-off-by: Steven Rostedt (Google) <rost...@goodmis.org>
---
 kernel/trace/trace.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8e9853d38c8d..b3b36d7f1201 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7567,6 +7567,7 @@ struct ftrace_buffer_info {
        struct trace_iterator   iter;
        void                    *spare;
        unsigned int            spare_cpu;
+       unsigned int            spare_size;
        unsigned int            read;
 };
 
@@ -8286,6 +8287,15 @@ tracing_buffers_read(struct file *filp, char __user 
*ubuf,
 
        page_size = ring_buffer_subbuf_size_get(iter->array_buffer->buffer);
 
+       /* Make sure the spare matches the current sub buffer size */
+       if (info->spare) {
+               if (page_size != info->spare_size) {
+                       ring_buffer_free_read_page(iter->array_buffer->buffer,
+                                                  info->spare_cpu, 
info->spare);
+                       info->spare = NULL;
+               }
+       }
+
        if (!info->spare) {
                info->spare = 
ring_buffer_alloc_read_page(iter->array_buffer->buffer,
                                                          iter->cpu_file);
@@ -8294,6 +8304,7 @@ tracing_buffers_read(struct file *filp, char __user *ubuf,
                        info->spare = NULL;
                } else {
                        info->spare_cpu = iter->cpu_file;
+                       info->spare_size = page_size;
                }
        }
        if (!info->spare)
-- 
2.42.0