ring_buffer: allocate buffer page pointer

The current method of overlaying the page frame as the buffer page pointer
can be very dangerous and limits our ability to do other things with
a page from the buffer, like send it off to disk.

This patch allocates the buffer_page instead of overlaying the page's
page frame. The use of the buffer_page has hardly changed due to this.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 32 insertions, 22 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 9631abf2ae2..98145718988 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -115,16 +115,10 @@ void *ring_buffer_event_data(struct ring_buffer_event *event)
  * Thanks to Peter Zijlstra for suggesting this idea.
  */
 struct buffer_page {
-        union {
-                struct {
-                        unsigned long    flags;         /* mandatory */
-                        atomic_t         _count;        /* mandatory */
-                        u64              time_stamp;    /* page time stamp */
-                        unsigned         size;          /* size of page data */
-                        struct list_head list;          /* list of free pages */
-                };
-                struct page page;
-        };
+        u64              time_stamp;    /* page time stamp */
+        unsigned         size;          /* size of page data */
+        struct list_head list;          /* list of free pages */
+        void *page;                     /* Actual data page */
 };
 
 /*
@@ -133,9 +127,9 @@ struct buffer_page {
  */
 static inline void free_buffer_page(struct buffer_page *bpage)
 {
-        reset_page_mapcount(&bpage->page);
-        bpage->page.mapping = NULL;
-        __free_page(&bpage->page);
+        if (bpage->page)
+                __free_page(bpage->page);
+        kfree(bpage);
 }
 
 /*
@@ -237,11 +231,16 @@ static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
         unsigned i;
 
         for (i = 0; i < nr_pages; i++) {
+                page = kzalloc_node(ALIGN(sizeof(*page), cache_line_size()),
+                                    GFP_KERNEL, cpu_to_node(cpu));
+                if (!page)
+                        goto free_pages;
+                list_add(&page->list, &pages);
+
                 addr = __get_free_page(GFP_KERNEL);
                 if (!addr)
                         goto free_pages;
-                page = (struct buffer_page *)virt_to_page(addr);
-                list_add(&page->list, &pages);
+                page->page = (void *)addr;
         }
 
         list_splice(&pages, head);
@@ -262,6 +261,7 @@ static struct ring_buffer_per_cpu *
 rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
 {
         struct ring_buffer_per_cpu *cpu_buffer;
+        struct buffer_page *page;
         unsigned long addr;
         int ret;
 
@@ -275,10 +275,17 @@ rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
         spin_lock_init(&cpu_buffer->lock);
         INIT_LIST_HEAD(&cpu_buffer->pages);
 
+        page = kzalloc_node(ALIGN(sizeof(*page), cache_line_size()),
+                            GFP_KERNEL, cpu_to_node(cpu));
+        if (!page)
+                goto fail_free_buffer;
+
+        cpu_buffer->reader_page = page;
         addr = __get_free_page(GFP_KERNEL);
         if (!addr)
-                goto fail_free_buffer;
-        cpu_buffer->reader_page = (struct buffer_page *)virt_to_page(addr);
+                goto fail_free_reader;
+        page->page = (void *)addr;
+
         INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
         cpu_buffer->reader_page->size = 0;
 
@@ -523,11 +530,16 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
 
         for_each_buffer_cpu(buffer, cpu) {
                 for (i = 0; i < new_pages; i++) {
+                        page = kzalloc_node(ALIGN(sizeof(*page),
+                                                  cache_line_size()),
+                                            GFP_KERNEL, cpu_to_node(cpu));
+                        if (!page)
+                                goto free_pages;
+                        list_add(&page->list, &pages);
                         addr = __get_free_page(GFP_KERNEL);
                         if (!addr)
                                 goto free_pages;
-                        page = (struct buffer_page *)virt_to_page(addr);
-                        list_add(&page->list, &pages);
+                        page->page = (void *)addr;
                 }
         }
 
@@ -567,9 +579,7 @@ static inline int rb_null_event(struct ring_buffer_event *event)
 
 static inline void *rb_page_index(struct buffer_page *page, unsigned index)
 {
-        void *addr = page_address(&page->page);
-
-        return addr + index;
+        return page->page + index;
 }
 
 static inline struct ring_buffer_event *