[PATCH v1] ring-buffer: Skip si_mem_available() for persistent and remote buffers

[Vincent Donnefort]

Persistent and remote buffer memory is pre-allocated by the time
__rb_allocate_pages() is called. Skip si_mem_available() to avoid
wrongly failing the allocation under memory pressure.

For the same reason, unset user_thread.

Fixes: be68d63a139b ("ring-buffer: Add ring_buffer_alloc_range()")
Fixes: 2e67fabd8b77 ("ring-buffer: Introduce ring-buffer remotes")
Signed-off-by: Vincent Donnefort <vdonnef...@google.com>
---
 kernel/trace/ring_buffer.c | 41 +++++++++++++++++++-------------------
 1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 04bb94c29f58..b3a30a0413a5 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2442,20 +2442,30 @@ static int __rb_allocate_pages(struct 
ring_buffer_per_cpu *cpu_buffer,
        struct trace_buffer *buffer = cpu_buffer->buffer;
        struct ring_buffer_cpu_meta *meta = NULL;
        struct buffer_page *bpage, *tmp;
-       bool user_thread = current->mm != NULL;
        struct ring_buffer_desc *desc = NULL;
+       bool user_thread = false;
        long i;
 
-       /*
-        * Check if the available memory is there first.
-        * Note, si_mem_available() only gives us a rough estimate of available
-        * memory. It may not be accurate. But we don't care, we just want
-        * to prevent doing any allocation when it is obvious that it is
-        * not going to succeed.
-        */
-       i = si_mem_available();
-       if (i < nr_pages)
-               return -ENOMEM;
+       if (buffer->range_addr_start) {
+               meta = rb_range_meta(buffer, nr_pages, cpu_buffer->cpu);
+       } else if (buffer->remote) {
+               desc = ring_buffer_desc(buffer->remote->desc, cpu_buffer->cpu);
+               if (!desc || WARN_ON(desc->nr_page_va != (nr_pages + 1)))
+                       return -EINVAL;
+       } else {
+               /*
+                * Check if the available memory is there first.
+                * Note, si_mem_available() only gives us a rough estimate of 
available
+                * memory. It may not be accurate. But we don't care, we just 
want
+                * to prevent doing any allocation when it is obvious that it is
+                * not going to succeed.
+                */
+               i = si_mem_available();
+               if (i < nr_pages)
+                       return -ENOMEM;
+
+               user_thread = current->mm != NULL;
+       }
 
        /*
         * If a user thread allocates too much, and si_mem_available()
@@ -2469,15 +2479,6 @@ static int __rb_allocate_pages(struct 
ring_buffer_per_cpu *cpu_buffer,
        if (user_thread)
                set_current_oom_origin();
 
-       if (buffer->range_addr_start)
-               meta = rb_range_meta(buffer, nr_pages, cpu_buffer->cpu);
-
-       if (buffer->remote) {
-               desc = ring_buffer_desc(buffer->remote->desc, cpu_buffer->cpu);
-               if (!desc || WARN_ON(desc->nr_page_va != (nr_pages + 1)))
-                       return -EINVAL;
-       }
-
        for (i = 0; i < nr_pages; i++) {
 
                bpage = alloc_cpu_page(cpu_buffer->cpu);

base-commit: 24a19b953e2a3d0ea5a8c4951a0ab8f32720c907
-- 
2.56.0.385.gd3acb90ef8-goog