[PATCH v2 2/3] tracing/remotes: Fix struct_len in trace_remote_alloc_buffer()

[Vincent Donnefort]

Pre-calculate desc->struct_len up-front in trace_remote_alloc_buffer()
with trace_buffer_desc_size() to fix double-counting.

While at it, use the accessor __first_ring_buffer_desc().

Fixes: 96e43537af54 ("tracing: Introduce trace remotes")
Reported-by: Sashiko <sashiko-...@kernel.org>
Signed-off-by: Vincent Donnefort <vdonnef...@google.com>

diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index d48042239d58..0f6ef5c36d84 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -979,27 +979,22 @@ EXPORT_SYMBOL_GPL(trace_remote_free_buffer);
 int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t 
desc_size, size_t buffer_size,
                              const struct cpumask *cpumask)
 {
+       size_t min_desc_size = trace_buffer_desc_size(buffer_size, 
cpumask_weight(cpumask));
        unsigned int nr_pages = max(DIV_ROUND_UP(buffer_size, PAGE_SIZE), 2UL) 
+ 1;
-       void *desc_end = desc + desc_size;
        struct ring_buffer_desc *rb_desc;
        int cpu, ret = -ENOMEM;
 
-       if (desc_size < struct_size(desc, __data, 0))
+       if (desc_size < min_desc_size)
                return -EINVAL;
 
        desc->nr_cpus = 0;
-       desc->struct_len = struct_size(desc, __data, 0);
+       desc->struct_len = min_desc_size;
 
-       rb_desc = (struct ring_buffer_desc *)&desc->__data[0];
+       rb_desc = __first_ring_buffer_desc(desc);
 
        for_each_cpu(cpu, cpumask) {
                unsigned int id;
 
-               if ((void *)rb_desc + struct_size(rb_desc, page_va, nr_pages) > 
desc_end) {
-                       ret = -EINVAL;
-                       goto err;
-               }
-
                rb_desc->cpu = cpu;
                rb_desc->nr_page_va = 0;
                rb_desc->meta_va = (unsigned long)__get_free_page(GFP_KERNEL);
@@ -1015,8 +1010,6 @@ int trace_remote_alloc_buffer(struct trace_buffer_desc 
*desc, size_t desc_size,
 
                        rb_desc->nr_page_va++;
                }
-               desc->struct_len += offsetof(struct ring_buffer_desc, page_va);
-               desc->struct_len += struct_size(rb_desc, page_va, 
rb_desc->nr_page_va);
                rb_desc = __next_ring_buffer_desc(rb_desc);
        }
 
-- 
2.55.0.795.g602f6c329a-goog