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Subject[PATCH v5 08/15] ring-buffer: Make sure the spare sub buffer used for reads has same size
From: "Steven Rostedt (Google)" <rostedt@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) <rostedt@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 711095aa731d..4dcdc30aa110 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7582,6 +7582,7 @@ struct ftrace_buffer_info {
struct trace_iterator iter;
void *spare;
unsigned int spare_cpu;
+ unsigned int spare_size;
unsigned int read;
};

@@ -8301,6 +8302,15 @@ 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);
@@ -8309,6 +8319,7 @@ 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


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