ring-buffer: Make sure the spare sub buffer used for reads has same size

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.

Link: https://lore.kernel.org/linux-trace-kernel/20231219185629.763664788@goodmis.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tzvetomir Stoyanov <tz.stoyanov@gmail.com>
Cc: Vincent Donnefort <vdonnefort@google.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 711095aa731d33afc5b07f6cb124f6c6bced3221..4dcdc30aa1100b2899be7b7229f2abc8de2130bf 100644 (file)
--- 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)