[PATCH v2 1/2] ring-buffer: Skip si_mem_available() for persistent and remote buffers

[Vincent Donnefort <vdonnefort@google.com>]

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 <vdonnefort@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);
-- 
2.56.0.385.gd3acb90ef8-goog