1 files changed, 32 insertions, 17 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index bf27bb7a63e2..7c0168ad6d51 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -406,7 +406,7 @@ struct ring_buffer_per_cpu {
         spinlock_t                      reader_lock; /* serialize readers */
         raw_spinlock_t                  lock;
         struct lock_class_key           lock_key;
-        struct list_head                pages;
+        struct list_head                *pages;
         struct buffer_page              *head_page;     /* read from head */
         struct buffer_page              *tail_page;     /* write to tail */
         struct buffer_page              *commit_page;   /* committed pages */
@@ -498,7 +498,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
  */
 static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
 {
-        struct list_head *head = &cpu_buffer->pages;
+        struct list_head *head = cpu_buffer->pages;
         struct buffer_page *bpage, *tmp;
 
         if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
@@ -521,12 +521,13 @@ static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
 static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
                              unsigned nr_pages)
 {
-        struct list_head *head = &cpu_buffer->pages;
         struct buffer_page *bpage, *tmp;
         unsigned long addr;
         LIST_HEAD(pages);
         unsigned i;
 
+        WARN_ON(!nr_pages);
+
         for (i = 0; i < nr_pages; i++) {
                 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
                                     GFP_KERNEL, cpu_to_node(cpu_buffer->cpu));
@@ -541,7 +542,13 @@ static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
                 rb_init_page(bpage->page);
         }
 
-        list_splice(&pages, head);
+        /*
+         * The ring buffer page list is a circular list that does not
+         * start and end with a list head. All page list items point to
+         * other pages.
+         */
+        cpu_buffer->pages = pages.next;
+        list_del(&pages);
 
         rb_check_pages(cpu_buffer);
 
@@ -573,7 +580,6 @@ rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
         spin_lock_init(&cpu_buffer->reader_lock);
         lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
         cpu_buffer->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
-        INIT_LIST_HEAD(&cpu_buffer->pages);
 
         bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
                             GFP_KERNEL, cpu_to_node(cpu));
@@ -594,7 +600,7 @@ rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
                 goto fail_free_reader;
 
         cpu_buffer->head_page
-                = list_entry(cpu_buffer->pages.next, struct buffer_page, list);
+                = list_entry(cpu_buffer->pages, struct buffer_page, list);
         cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
 
         return cpu_buffer;
@@ -609,15 +615,20 @@ rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
 
 static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
 {
-        struct list_head *head = &cpu_buffer->pages;
+        struct list_head *head = cpu_buffer->pages;
         struct buffer_page *bpage, *tmp;
 
         free_buffer_page(cpu_buffer->reader_page);
 
-        list_for_each_entry_safe(bpage, tmp, head, list) {
-                list_del_init(&bpage->list);
+        if (head) {
+                list_for_each_entry_safe(bpage, tmp, head, list) {
+                        list_del_init(&bpage->list);
+                        free_buffer_page(bpage);
+                }
+                bpage = list_entry(head, struct buffer_page, list);
                 free_buffer_page(bpage);
         }
+
         kfree(cpu_buffer);
 }
 
@@ -760,14 +771,14 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
         synchronize_sched();
 
         for (i = 0; i < nr_pages; i++) {
-                if (RB_WARN_ON(cpu_buffer, list_empty(&cpu_buffer->pages)))
+                if (RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages)))
                         return;
-                p = cpu_buffer->pages.next;
+                p = cpu_buffer->pages->next;
                 bpage = list_entry(p, struct buffer_page, list);
                 list_del_init(&bpage->list);
                 free_buffer_page(bpage);
         }
-        if (RB_WARN_ON(cpu_buffer, list_empty(&cpu_buffer->pages)))
+        if (RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages)))
                 return;
 
         rb_reset_cpu(cpu_buffer);
@@ -795,7 +806,7 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
                 p = pages->next;
                 bpage = list_entry(p, struct buffer_page, list);
                 list_del_init(&bpage->list);
-                list_add_tail(&bpage->list, &cpu_buffer->pages);
+                list_add_tail(&bpage->list, cpu_buffer->pages);
         }
         rb_reset_cpu(cpu_buffer);
 
@@ -992,9 +1003,6 @@ static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
 {
         struct list_head *p = (*bpage)->list.next;
 
-        if (p == &cpu_buffer->pages)
-                p = p->next;
-
         *bpage = list_entry(p, struct buffer_page, list);
 }
 
@@ -2247,6 +2255,13 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
         cpu_buffer->reader_page->list.next = reader->list.next;
         cpu_buffer->reader_page->list.prev = reader->list.prev;
 
+        /*
+         * cpu_buffer->pages just needs to point to the buffer, it
+         *  has no specific buffer page to point to. Lets move it out
+         *  of our way so we don't accidently swap it.
+         */
+        cpu_buffer->pages = reader->list.prev;
+
         local_set(&cpu_buffer->reader_page->write, 0);
         local_set(&cpu_buffer->reader_page->entries, 0);
         local_set(&cpu_buffer->reader_page->page->commit, 0);
@@ -2719,7 +2734,7 @@ static void
 rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
 {
         cpu_buffer->head_page
-                = list_entry(cpu_buffer->pages.next, struct buffer_page, list);
+                = list_entry(cpu_buffer->pages, struct buffer_page, list);
         local_set(&cpu_buffer->head_page->write, 0);
         local_set(&cpu_buffer->head_page->entries, 0);
         local_set(&cpu_buffer->head_page->page->commit, 0);