1 files changed, 889 insertions, 236 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index a330513d96ce..d4ff01970547 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -201,8 +201,6 @@ int tracing_is_on(void)
 }
 EXPORT_SYMBOL_GPL(tracing_is_on);
 
-#include "trace.h"
-
 #define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
 #define RB_ALIGNMENT            4U
 #define RB_MAX_SMALL_DATA       (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
@@ -218,17 +216,12 @@ enum {
 
 static inline int rb_null_event(struct ring_buffer_event *event)
 {
-        return event->type_len == RINGBUF_TYPE_PADDING
-                        && event->time_delta == 0;
-}
-
-static inline int rb_discarded_event(struct ring_buffer_event *event)
-{
-        return event->type_len == RINGBUF_TYPE_PADDING && event->time_delta;
+        return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
 }
 
 static void rb_event_set_padding(struct ring_buffer_event *event)
 {
+        /* padding has a NULL time_delta */
         event->type_len = RINGBUF_TYPE_PADDING;
         event->time_delta = 0;
 }
@@ -322,6 +315,14 @@ struct buffer_data_page {
         unsigned char    data[];        /* data of buffer page */
 };
 
+/*
+ * Note, the buffer_page list must be first. The buffer pages
+ * are allocated in cache lines, which means that each buffer
+ * page will be at the beginning of a cache line, and thus
+ * the least significant bits will be zero. We use this to
+ * add flags in the list struct pointers, to make the ring buffer
+ * lockless.
+ */
 struct buffer_page {
         struct list_head list;          /* list of buffer pages */
         local_t          write;         /* index for next write */
@@ -330,6 +331,21 @@ struct buffer_page {
         struct buffer_data_page *page;  /* Actual data page */
 };
 
+/*
+ * The buffer page counters, write and entries, must be reset
+ * atomically when crossing page boundaries. To synchronize this
+ * update, two counters are inserted into the number. One is
+ * the actual counter for the write position or count on the page.
+ *
+ * The other is a counter of updaters. Before an update happens
+ * the update partition of the counter is incremented. This will
+ * allow the updater to update the counter atomically.
+ *
+ * The counter is 20 bits, and the state data is 12.
+ */
+#define RB_WRITE_MASK           0xfffff
+#define RB_WRITE_INTCNT         (1 << 20)
+
 static void rb_init_page(struct buffer_data_page *bpage)
 {
         local_set(&bpage->commit, 0);
@@ -403,21 +419,20 @@ int ring_buffer_print_page_header(struct trace_seq *s)
 struct ring_buffer_per_cpu {
         int                             cpu;
         struct ring_buffer              *buffer;
-        spinlock_t                      reader_lock; /* serialize readers */
+        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 */
         struct buffer_page              *reader_page;
-        unsigned long                   nmi_dropped;
-        unsigned long                   commit_overrun;
-        unsigned long                   overrun;
-        unsigned long                   read;
+        local_t                         commit_overrun;
+        local_t                         overrun;
         local_t                         entries;
         local_t                         committing;
         local_t                         commits;
+        unsigned long                   read;
         u64                             write_stamp;
         u64                             read_stamp;
         atomic_t                        record_disabled;
@@ -450,14 +465,19 @@ struct ring_buffer_iter {
 };
 
 /* buffer may be either ring_buffer or ring_buffer_per_cpu */
-#define RB_WARN_ON(buffer, cond)                                \
-        ({                                                      \
-                int _____ret = unlikely(cond);                  \
-                if (_____ret) {                                 \
-                        atomic_inc(&buffer->record_disabled);   \
-                        WARN_ON(1);                             \
-                }                                               \
-                _____ret;                                       \
+#define RB_WARN_ON(b, cond)                                             \
+        ({                                                              \
+                int _____ret = unlikely(cond);                          \
+                if (_____ret) {                                         \
+                        if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
+                                struct ring_buffer_per_cpu *__b =       \
+                                        (void *)b;                      \
+                                atomic_inc(&__b->buffer->record_disabled); \
+                        } else                                          \
+                                atomic_inc(&b->record_disabled);        \
+                        WARN_ON(1);                                     \
+                }                                                       \
+                _____ret;                                               \
         })
 
 /* Up this if you want to test the TIME_EXTENTS and normalization */
@@ -489,6 +509,390 @@ void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
 }
 EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
 
+/*
+ * Making the ring buffer lockless makes things tricky.
+ * Although writes only happen on the CPU that they are on,
+ * and they only need to worry about interrupts. Reads can
+ * happen on any CPU.
+ *
+ * The reader page is always off the ring buffer, but when the
+ * reader finishes with a page, it needs to swap its page with
+ * a new one from the buffer. The reader needs to take from
+ * the head (writes go to the tail). But if a writer is in overwrite
+ * mode and wraps, it must push the head page forward.
+ *
+ * Here lies the problem.
+ *
+ * The reader must be careful to replace only the head page, and
+ * not another one. As described at the top of the file in the
+ * ASCII art, the reader sets its old page to point to the next
+ * page after head. It then sets the page after head to point to
+ * the old reader page. But if the writer moves the head page
+ * during this operation, the reader could end up with the tail.
+ *
+ * We use cmpxchg to help prevent this race. We also do something
+ * special with the page before head. We set the LSB to 1.
+ *
+ * When the writer must push the page forward, it will clear the
+ * bit that points to the head page, move the head, and then set
+ * the bit that points to the new head page.
+ *
+ * We also don't want an interrupt coming in and moving the head
+ * page on another writer. Thus we use the second LSB to catch
+ * that too. Thus:
+ *
+ * head->list->prev->next        bit 1          bit 0
+ *                              -------        -------
+ * Normal page                     0              0
+ * Points to head page             0              1
+ * New head page                   1              0
+ *
+ * Note we can not trust the prev pointer of the head page, because:
+ *
+ * +----+       +-----+        +-----+
+ * |    |------>|  T  |---X--->|  N  |
+ * |    |<------|     |        |     |
+ * +----+       +-----+        +-----+
+ *   ^                           ^ |
+ *   |          +-----+          | |
+ *   +----------|  R  |----------+ |
+ *              |     |<-----------+
+ *              +-----+
+ *
+ * Key:  ---X-->  HEAD flag set in pointer
+ *         T      Tail page
+ *         R      Reader page
+ *         N      Next page
+ *
+ * (see __rb_reserve_next() to see where this happens)
+ *
+ *  What the above shows is that the reader just swapped out
+ *  the reader page with a page in the buffer, but before it
+ *  could make the new header point back to the new page added
+ *  it was preempted by a writer. The writer moved forward onto
+ *  the new page added by the reader and is about to move forward
+ *  again.
+ *
+ *  You can see, it is legitimate for the previous pointer of
+ *  the head (or any page) not to point back to itself. But only
+ *  temporarially.
+ */
+
+#define RB_PAGE_NORMAL          0UL
+#define RB_PAGE_HEAD            1UL
+#define RB_PAGE_UPDATE          2UL
+
+
+#define RB_FLAG_MASK            3UL
+
+/* PAGE_MOVED is not part of the mask */
+#define RB_PAGE_MOVED           4UL
+
+/*
+ * rb_list_head - remove any bit
+ */
+static struct list_head *rb_list_head(struct list_head *list)
+{
+        unsigned long val = (unsigned long)list;
+
+        return (struct list_head *)(val & ~RB_FLAG_MASK);
+}
+
+/*
+ * rb_is_head_page - test if the give page is the head page
+ *
+ * Because the reader may move the head_page pointer, we can
+ * not trust what the head page is (it may be pointing to
+ * the reader page). But if the next page is a header page,
+ * its flags will be non zero.
+ */
+static int inline
+rb_is_head_page(struct ring_buffer_per_cpu *cpu_buffer,
+                struct buffer_page *page, struct list_head *list)
+{
+        unsigned long val;
+
+        val = (unsigned long)list->next;
+
+        if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
+                return RB_PAGE_MOVED;
+
+        return val & RB_FLAG_MASK;
+}
+
+/*
+ * rb_is_reader_page
+ *
+ * The unique thing about the reader page, is that, if the
+ * writer is ever on it, the previous pointer never points
+ * back to the reader page.
+ */
+static int rb_is_reader_page(struct buffer_page *page)
+{
+        struct list_head *list = page->list.prev;
+
+        return rb_list_head(list->next) != &page->list;
+}
+
+/*
+ * rb_set_list_to_head - set a list_head to be pointing to head.
+ */
+static void rb_set_list_to_head(struct ring_buffer_per_cpu *cpu_buffer,
+                                struct list_head *list)
+{
+        unsigned long *ptr;
+
+        ptr = (unsigned long *)&list->next;
+        *ptr |= RB_PAGE_HEAD;
+        *ptr &= ~RB_PAGE_UPDATE;
+}
+
+/*
+ * rb_head_page_activate - sets up head page
+ */
+static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
+{
+        struct buffer_page *head;
+
+        head = cpu_buffer->head_page;
+        if (!head)
+                return;
+
+        /*
+         * Set the previous list pointer to have the HEAD flag.
+         */
+        rb_set_list_to_head(cpu_buffer, head->list.prev);
+}
+
+static void rb_list_head_clear(struct list_head *list)
+{
+        unsigned long *ptr = (unsigned long *)&list->next;
+
+        *ptr &= ~RB_FLAG_MASK;
+}
+
+/*
+ * rb_head_page_dactivate - clears head page ptr (for free list)
+ */
+static void
+rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
+{
+        struct list_head *hd;
+
+        /* Go through the whole list and clear any pointers found. */
+        rb_list_head_clear(cpu_buffer->pages);
+
+        list_for_each(hd, cpu_buffer->pages)
+                rb_list_head_clear(hd);
+}
+
+static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
+                            struct buffer_page *head,
+                            struct buffer_page *prev,
+                            int old_flag, int new_flag)
+{
+        struct list_head *list;
+        unsigned long val = (unsigned long)&head->list;
+        unsigned long ret;
+
+        list = &prev->list;
+
+        val &= ~RB_FLAG_MASK;
+
+        ret = cmpxchg((unsigned long *)&list->next,
+                      val | old_flag, val | new_flag);
+
+        /* check if the reader took the page */
+        if ((ret & ~RB_FLAG_MASK) != val)
+                return RB_PAGE_MOVED;
+
+        return ret & RB_FLAG_MASK;
+}
+
+static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
+                                   struct buffer_page *head,
+                                   struct buffer_page *prev,
+                                   int old_flag)
+{
+        return rb_head_page_set(cpu_buffer, head, prev,
+                                old_flag, RB_PAGE_UPDATE);
+}
+
+static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
+                                 struct buffer_page *head,
+                                 struct buffer_page *prev,
+                                 int old_flag)
+{
+        return rb_head_page_set(cpu_buffer, head, prev,
+                                old_flag, RB_PAGE_HEAD);
+}
+
+static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
+                                   struct buffer_page *head,
+                                   struct buffer_page *prev,
+                                   int old_flag)
+{
+        return rb_head_page_set(cpu_buffer, head, prev,
+                                old_flag, RB_PAGE_NORMAL);
+}
+
+static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
+                               struct buffer_page **bpage)
+{
+        struct list_head *p = rb_list_head((*bpage)->list.next);
+
+        *bpage = list_entry(p, struct buffer_page, list);
+}
+
+static struct buffer_page *
+rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+        struct buffer_page *head;
+        struct buffer_page *page;
+        struct list_head *list;
+        int i;
+
+        if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
+                return NULL;
+
+        /* sanity check */
+        list = cpu_buffer->pages;
+        if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
+                return NULL;
+
+        page = head = cpu_buffer->head_page;
+        /*
+         * It is possible that the writer moves the header behind
+         * where we started, and we miss in one loop.
+         * A second loop should grab the header, but we'll do
+         * three loops just because I'm paranoid.
+         */
+        for (i = 0; i < 3; i++) {
+                do {
+                        if (rb_is_head_page(cpu_buffer, page, page->list.prev)) {
+                                cpu_buffer->head_page = page;
+                                return page;
+                        }
+                        rb_inc_page(cpu_buffer, &page);
+                } while (page != head);
+        }
+
+        RB_WARN_ON(cpu_buffer, 1);
+
+        return NULL;
+}
+
+static int rb_head_page_replace(struct buffer_page *old,
+                                struct buffer_page *new)
+{
+        unsigned long *ptr = (unsigned long *)&old->list.prev->next;
+        unsigned long val;
+        unsigned long ret;
+
+        val = *ptr & ~RB_FLAG_MASK;
+        val |= RB_PAGE_HEAD;
+
+        ret = cmpxchg(ptr, val, (unsigned long)&new->list);
+
+        return ret == val;
+}
+
+/*
+ * rb_tail_page_update - move the tail page forward
+ *
+ * Returns 1 if moved tail page, 0 if someone else did.
+ */
+static int rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
+                               struct buffer_page *tail_page,
+                               struct buffer_page *next_page)
+{
+        struct buffer_page *old_tail;
+        unsigned long old_entries;
+        unsigned long old_write;
+        int ret = 0;
+
+        /*
+         * The tail page now needs to be moved forward.
+         *
+         * We need to reset the tail page, but without messing
+         * with possible erasing of data brought in by interrupts
+         * that have moved the tail page and are currently on it.
+         *
+         * We add a counter to the write field to denote this.
+         */
+        old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
+        old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
+
+        /*
+         * Just make sure we have seen our old_write and synchronize
+         * with any interrupts that come in.
+         */
+        barrier();
+
+        /*
+         * If the tail page is still the same as what we think
+         * it is, then it is up to us to update the tail
+         * pointer.
+         */
+        if (tail_page == cpu_buffer->tail_page) {
+                /* Zero the write counter */
+                unsigned long val = old_write & ~RB_WRITE_MASK;
+                unsigned long eval = old_entries & ~RB_WRITE_MASK;
+
+                /*
+                 * This will only succeed if an interrupt did
+                 * not come in and change it. In which case, we
+                 * do not want to modify it.
+                 *
+                 * We add (void) to let the compiler know that we do not care
+                 * about the return value of these functions. We use the
+                 * cmpxchg to only update if an interrupt did not already
+                 * do it for us. If the cmpxchg fails, we don't care.
+                 */
+                (void)local_cmpxchg(&next_page->write, old_write, val);
+                (void)local_cmpxchg(&next_page->entries, old_entries, eval);
+
+                /*
+                 * No need to worry about races with clearing out the commit.
+                 * it only can increment when a commit takes place. But that
+                 * only happens in the outer most nested commit.
+                 */
+                local_set(&next_page->page->commit, 0);
+
+                old_tail = cmpxchg(&cpu_buffer->tail_page,
+                                   tail_page, next_page);
+
+                if (old_tail == tail_page)
+                        ret = 1;
+        }
+
+        return ret;
+}
+
+static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
+                          struct buffer_page *bpage)
+{
+        unsigned long val = (unsigned long)bpage;
+
+        if (RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK))
+                return 1;
+
+        return 0;
+}
+
+/**
+ * rb_check_list - make sure a pointer to a list has the last bits zero
+ */
+static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
+                         struct list_head *list)
+{
+        if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
+                return 1;
+        if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
+                return 1;
+        return 0;
+}
+
 /**
  * check_pages - integrity check of buffer pages
  * @cpu_buffer: CPU buffer with pages to test
@@ -498,14 +902,19 @@ 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;
 
+        rb_head_page_deactivate(cpu_buffer);
+
         if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
                 return -1;
         if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
                 return -1;
 
+        if (rb_check_list(cpu_buffer, head))
+                return -1;
+
         list_for_each_entry_safe(bpage, tmp, head, list) {
                 if (RB_WARN_ON(cpu_buffer,
                                bpage->list.next->prev != &bpage->list))
@@ -513,25 +922,33 @@ static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
                 if (RB_WARN_ON(cpu_buffer,
                                bpage->list.prev->next != &bpage->list))
                         return -1;
+                if (rb_check_list(cpu_buffer, &bpage->list))
+                        return -1;
         }
 
+        rb_head_page_activate(cpu_buffer);
+
         return 0;
 }
 
 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));
                 if (!bpage)
                         goto free_pages;
+
+                rb_check_bpage(cpu_buffer, bpage);
+
                 list_add(&bpage->list, &pages);
 
                 addr = __get_free_page(GFP_KERNEL);
@@ -541,7 +958,13 @@ 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);
 
@@ -573,13 +996,14 @@ 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));
         if (!bpage)
                 goto fail_free_buffer;
 
+        rb_check_bpage(cpu_buffer, bpage);
+
         cpu_buffer->reader_page = bpage;
         addr = __get_free_page(GFP_KERNEL);
         if (!addr)
@@ -594,9 +1018,11 @@ 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;
 
+        rb_head_page_activate(cpu_buffer);
+
         return cpu_buffer;
 
  fail_free_reader:
@@ -609,15 +1035,22 @@ 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);
+        rb_head_page_deactivate(cpu_buffer);
+
+        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);
 }
 
@@ -760,15 +1193,17 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
         atomic_inc(&cpu_buffer->record_disabled);
         synchronize_sched();
 
+        rb_head_page_deactivate(cpu_buffer);
+
         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);
@@ -790,15 +1225,19 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
         atomic_inc(&cpu_buffer->record_disabled);
         synchronize_sched();
 
+        spin_lock_irq(&cpu_buffer->reader_lock);
+        rb_head_page_deactivate(cpu_buffer);
+
         for (i = 0; i < nr_pages; i++) {
                 if (RB_WARN_ON(cpu_buffer, list_empty(pages)))
                         return;
                 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);
+        spin_unlock_irq(&cpu_buffer->reader_lock);
 
         rb_check_pages(cpu_buffer);
 
@@ -949,21 +1388,14 @@ rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
 }
 
 static inline struct ring_buffer_event *
-rb_head_event(struct ring_buffer_per_cpu *cpu_buffer)
-{
-        return __rb_page_index(cpu_buffer->head_page,
-                               cpu_buffer->head_page->read);
-}
-
-static inline struct ring_buffer_event *
 rb_iter_head_event(struct ring_buffer_iter *iter)
 {
         return __rb_page_index(iter->head_page, iter->head);
 }
 
-static inline unsigned rb_page_write(struct buffer_page *bpage)
+static inline unsigned long rb_page_write(struct buffer_page *bpage)
 {
-        return local_read(&bpage->write);
+        return local_read(&bpage->write) & RB_WRITE_MASK;
 }
 
 static inline unsigned rb_page_commit(struct buffer_page *bpage)
@@ -971,6 +1403,11 @@ static inline unsigned rb_page_commit(struct buffer_page *bpage)
         return local_read(&bpage->page->commit);
 }
 
+static inline unsigned long rb_page_entries(struct buffer_page *bpage)
+{
+        return local_read(&bpage->entries) & RB_WRITE_MASK;
+}
+
 /* Size is determined by what has been commited */
 static inline unsigned rb_page_size(struct buffer_page *bpage)
 {
@@ -983,22 +1420,6 @@ rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
         return rb_page_commit(cpu_buffer->commit_page);
 }
 
-static inline unsigned rb_head_size(struct ring_buffer_per_cpu *cpu_buffer)
-{
-        return rb_page_commit(cpu_buffer->head_page);
-}
-
-static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
-                               struct buffer_page **bpage)
-{
-        struct list_head *p = (*bpage)->list.next;
-
-        if (p == &cpu_buffer->pages)
-                p = p->next;
-
-        *bpage = list_entry(p, struct buffer_page, list);
-}
-
 static inline unsigned
 rb_event_index(struct ring_buffer_event *event)
 {
@@ -1024,6 +1445,8 @@ rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
 static void
 rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
 {
+        unsigned long max_count;
+
         /*
          * We only race with interrupts and NMIs on this CPU.
          * If we own the commit event, then we can commit
@@ -1033,9 +1456,16 @@ rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
          * assign the commit to the tail.
          */
  again:
+        max_count = cpu_buffer->buffer->pages * 100;
+
         while (cpu_buffer->commit_page != cpu_buffer->tail_page) {
-                cpu_buffer->commit_page->page->commit =
-                        cpu_buffer->commit_page->write;
+                if (RB_WARN_ON(cpu_buffer, !(--max_count)))
+                        return;
+                if (RB_WARN_ON(cpu_buffer,
+                               rb_is_reader_page(cpu_buffer->tail_page)))
+                        return;
+                local_set(&cpu_buffer->commit_page->page->commit,
+                          rb_page_write(cpu_buffer->commit_page));
                 rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
                 cpu_buffer->write_stamp =
                         cpu_buffer->commit_page->page->time_stamp;
@@ -1044,8 +1474,12 @@ rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
         }
         while (rb_commit_index(cpu_buffer) !=
                rb_page_write(cpu_buffer->commit_page)) {
-                cpu_buffer->commit_page->page->commit =
-                        cpu_buffer->commit_page->write;
+
+                local_set(&cpu_buffer->commit_page->page->commit,
+                          rb_page_write(cpu_buffer->commit_page));
+                RB_WARN_ON(cpu_buffer,
+                           local_read(&cpu_buffer->commit_page->page->commit) &
+                           ~RB_WRITE_MASK);
                 barrier();
         }
 
@@ -1078,7 +1512,7 @@ static void rb_inc_iter(struct ring_buffer_iter *iter)
          * to the head page instead of next.
          */
         if (iter->head_page == cpu_buffer->reader_page)
-                iter->head_page = cpu_buffer->head_page;
+                iter->head_page = rb_set_head_page(cpu_buffer);
         else
                 rb_inc_page(cpu_buffer, &iter->head_page);
 
@@ -1122,6 +1556,163 @@ rb_update_event(struct ring_buffer_event *event,
         }
 }
 
+/*
+ * rb_handle_head_page - writer hit the head page
+ *
+ * Returns: +1 to retry page
+ *           0 to continue
+ *          -1 on error
+ */
+static int
+rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
+                    struct buffer_page *tail_page,
+                    struct buffer_page *next_page)
+{
+        struct buffer_page *new_head;
+        int entries;
+        int type;
+        int ret;
+
+        entries = rb_page_entries(next_page);
+
+        /*
+         * The hard part is here. We need to move the head
+         * forward, and protect against both readers on
+         * other CPUs and writers coming in via interrupts.
+         */
+        type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
+                                       RB_PAGE_HEAD);
+
+        /*
+         * type can be one of four:
+         *  NORMAL - an interrupt already moved it for us
+         *  HEAD   - we are the first to get here.
+         *  UPDATE - we are the interrupt interrupting
+         *           a current move.
+         *  MOVED  - a reader on another CPU moved the next
+         *           pointer to its reader page. Give up
+         *           and try again.
+         */
+
+        switch (type) {
+        case RB_PAGE_HEAD:
+                /*
+                 * We changed the head to UPDATE, thus
+                 * it is our responsibility to update
+                 * the counters.
+                 */
+                local_add(entries, &cpu_buffer->overrun);
+
+                /*
+                 * The entries will be zeroed out when we move the
+                 * tail page.
+                 */
+
+                /* still more to do */
+                break;
+
+        case RB_PAGE_UPDATE:
+                /*
+                 * This is an interrupt that interrupt the
+                 * previous update. Still more to do.
+                 */
+                break;
+        case RB_PAGE_NORMAL:
+                /*
+                 * An interrupt came in before the update
+                 * and processed this for us.
+                 * Nothing left to do.
+                 */
+                return 1;
+        case RB_PAGE_MOVED:
+                /*
+                 * The reader is on another CPU and just did
+                 * a swap with our next_page.
+                 * Try again.
+                 */
+                return 1;
+        default:
+                RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
+                return -1;
+        }
+
+        /*
+         * Now that we are here, the old head pointer is
+         * set to UPDATE. This will keep the reader from
+         * swapping the head page with the reader page.
+         * The reader (on another CPU) will spin till
+         * we are finished.
+         *
+         * We just need to protect against interrupts
+         * doing the job. We will set the next pointer
+         * to HEAD. After that, we set the old pointer
+         * to NORMAL, but only if it was HEAD before.
+         * otherwise we are an interrupt, and only
+         * want the outer most commit to reset it.
+         */
+        new_head = next_page;
+        rb_inc_page(cpu_buffer, &new_head);
+
+        ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
+                                    RB_PAGE_NORMAL);
+
+        /*
+         * Valid returns are:
+         *  HEAD   - an interrupt came in and already set it.
+         *  NORMAL - One of two things:
+         *            1) We really set it.
+         *            2) A bunch of interrupts came in and moved
+         *               the page forward again.
+         */
+        switch (ret) {
+        case RB_PAGE_HEAD:
+        case RB_PAGE_NORMAL:
+                /* OK */
+                break;
+        default:
+                RB_WARN_ON(cpu_buffer, 1);
+                return -1;
+        }
+
+        /*
+         * It is possible that an interrupt came in,
+         * set the head up, then more interrupts came in
+         * and moved it again. When we get back here,
+         * the page would have been set to NORMAL but we
+         * just set it back to HEAD.
+         *
+         * How do you detect this? Well, if that happened
+         * the tail page would have moved.
+         */
+        if (ret == RB_PAGE_NORMAL) {
+                /*
+                 * If the tail had moved passed next, then we need
+                 * to reset the pointer.
+                 */
+                if (cpu_buffer->tail_page != tail_page &&
+                    cpu_buffer->tail_page != next_page)
+                        rb_head_page_set_normal(cpu_buffer, new_head,
+                                                next_page,
+                                                RB_PAGE_HEAD);
+        }
+
+        /*
+         * If this was the outer most commit (the one that
+         * changed the original pointer from HEAD to UPDATE),
+         * then it is up to us to reset it to NORMAL.
+         */
+        if (type == RB_PAGE_HEAD) {
+                ret = rb_head_page_set_normal(cpu_buffer, next_page,
+                                              tail_page,
+                                              RB_PAGE_UPDATE);
+                if (RB_WARN_ON(cpu_buffer,
+                               ret != RB_PAGE_UPDATE))
+                        return -1;
+        }
+
+        return 0;
+}
+
 static unsigned rb_calculate_event_length(unsigned length)
 {
         struct ring_buffer_event event; /* Used only for sizeof array */
@@ -1185,9 +1776,6 @@ rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
         event->type_len = RINGBUF_TYPE_PADDING;
         /* time delta must be non zero */
         event->time_delta = 1;
-        /* Account for this as an entry */
-        local_inc(&tail_page->entries);
-        local_inc(&cpu_buffer->entries);
 
         /* Set write to end of buffer */
         length = (tail + length) - BUF_PAGE_SIZE;
@@ -1200,96 +1788,93 @@ rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
              struct buffer_page *commit_page,
              struct buffer_page *tail_page, u64 *ts)
 {
-        struct buffer_page *next_page, *head_page, *reader_page;
         struct ring_buffer *buffer = cpu_buffer->buffer;
-        bool lock_taken = false;
-        unsigned long flags;
+        struct buffer_page *next_page;
+        int ret;
 
         next_page = tail_page;
 
-        local_irq_save(flags);
-        /*
-         * Since the write to the buffer is still not
-         * fully lockless, we must be careful with NMIs.
-         * The locks in the writers are taken when a write
-         * crosses to a new page. The locks protect against
-         * races with the readers (this will soon be fixed
-         * with a lockless solution).
-         *
-         * Because we can not protect against NMIs, and we
-         * want to keep traces reentrant, we need to manage
-         * what happens when we are in an NMI.
-         *
-         * NMIs can happen after we take the lock.
-         * If we are in an NMI, only take the lock
-         * if it is not already taken. Otherwise
-         * simply fail.
-         */
-        if (unlikely(in_nmi())) {
-                if (!__raw_spin_trylock(&cpu_buffer->lock)) {
-                        cpu_buffer->nmi_dropped++;
-                        goto out_reset;
-                }
-        } else
-                __raw_spin_lock(&cpu_buffer->lock);
-
-        lock_taken = true;
-
         rb_inc_page(cpu_buffer, &next_page);
 
-        head_page = cpu_buffer->head_page;
-        reader_page = cpu_buffer->reader_page;
-
-        /* we grabbed the lock before incrementing */
-        if (RB_WARN_ON(cpu_buffer, next_page == reader_page))
-                goto out_reset;
-
         /*
          * If for some reason, we had an interrupt storm that made
          * it all the way around the buffer, bail, and warn
          * about it.
          */
         if (unlikely(next_page == commit_page)) {
-                cpu_buffer->commit_overrun++;
+                local_inc(&cpu_buffer->commit_overrun);
                 goto out_reset;
         }
 
-        if (next_page == head_page) {
-                if (!(buffer->flags & RB_FL_OVERWRITE))
-                        goto out_reset;
-
-                /* tail_page has not moved yet? */
-                if (tail_page == cpu_buffer->tail_page) {
-                        /* count overflows */
-                        cpu_buffer->overrun +=
-                                local_read(&head_page->entries);
+        /*
+         * This is where the fun begins!
+         *
+         * We are fighting against races between a reader that
+         * could be on another CPU trying to swap its reader
+         * page with the buffer head.
+         *
+         * We are also fighting against interrupts coming in and
+         * moving the head or tail on us as well.
+         *
+         * If the next page is the head page then we have filled
+         * the buffer, unless the commit page is still on the
+         * reader page.
+         */
+        if (rb_is_head_page(cpu_buffer, next_page, &tail_page->list)) {
 
-                        rb_inc_page(cpu_buffer, &head_page);
-                        cpu_buffer->head_page = head_page;
-                        cpu_buffer->head_page->read = 0;
+                /*
+                 * If the commit is not on the reader page, then
+                 * move the header page.
+                 */
+                if (!rb_is_reader_page(cpu_buffer->commit_page)) {
+                        /*
+                         * If we are not in overwrite mode,
+                         * this is easy, just stop here.
+                         */
+                        if (!(buffer->flags & RB_FL_OVERWRITE))
+                                goto out_reset;
+
+                        ret = rb_handle_head_page(cpu_buffer,
+                                                  tail_page,
+                                                  next_page);
+                        if (ret < 0)
+                                goto out_reset;
+                        if (ret)
+                                goto out_again;
+                } else {
+                        /*
+                         * We need to be careful here too. The
+                         * commit page could still be on the reader
+                         * page. We could have a small buffer, and
+                         * have filled up the buffer with events
+                         * from interrupts and such, and wrapped.
+                         *
+                         * Note, if the tail page is also the on the
+                         * reader_page, we let it move out.
+                         */
+                        if (unlikely((cpu_buffer->commit_page !=
+                                      cpu_buffer->tail_page) &&
+                                     (cpu_buffer->commit_page ==
+                                      cpu_buffer->reader_page))) {
+                                local_inc(&cpu_buffer->commit_overrun);
+                                goto out_reset;
+                        }
                 }
         }
 
-        /*
-         * If the tail page is still the same as what we think
-         * it is, then it is up to us to update the tail
-         * pointer.
-         */
-        if (tail_page == cpu_buffer->tail_page) {
-                local_set(&next_page->write, 0);
-                local_set(&next_page->entries, 0);
-                local_set(&next_page->page->commit, 0);
-                cpu_buffer->tail_page = next_page;
-
-                /* reread the time stamp */
+        ret = rb_tail_page_update(cpu_buffer, tail_page, next_page);
+        if (ret) {
+                /*
+                 * Nested commits always have zero deltas, so
+                 * just reread the time stamp
+                 */
                 *ts = rb_time_stamp(buffer, cpu_buffer->cpu);
-                cpu_buffer->tail_page->page->time_stamp = *ts;
+                next_page->page->time_stamp = *ts;
         }
 
-        rb_reset_tail(cpu_buffer, tail_page, tail, length);
+ out_again:
 
-        __raw_spin_unlock(&cpu_buffer->lock);
-        local_irq_restore(flags);
+        rb_reset_tail(cpu_buffer, tail_page, tail, length);
 
         /* fail and let the caller try again */
         return ERR_PTR(-EAGAIN);
@@ -1298,9 +1883,6 @@ rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
         /* reset write */
         rb_reset_tail(cpu_buffer, tail_page, tail, length);
 
-        if (likely(lock_taken))
-                __raw_spin_unlock(&cpu_buffer->lock);
-        local_irq_restore(flags);
         return NULL;
 }
 
@@ -1317,6 +1899,9 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
         barrier();
         tail_page = cpu_buffer->tail_page;
         write = local_add_return(length, &tail_page->write);
+
+        /* set write to only the index of the write */
+        write &= RB_WRITE_MASK;
         tail = write - length;
 
         /* See if we shot pass the end of this buffer page */
@@ -1361,12 +1946,16 @@ rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
         bpage = cpu_buffer->tail_page;
 
         if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
+                unsigned long write_mask =
+                        local_read(&bpage->write) & ~RB_WRITE_MASK;
                 /*
                  * This is on the tail page. It is possible that
                  * a write could come in and move the tail page
                  * and write to the next page. That is fine
                  * because we just shorten what is on this page.
                  */
+                old_index += write_mask;
+                new_index += write_mask;
                 index = local_cmpxchg(&bpage->write, old_index, new_index);
                 if (index == old_index)
                         return 1;
@@ -1482,7 +2071,8 @@ static void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
 }
 
 static struct ring_buffer_event *
-rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
+rb_reserve_next_event(struct ring_buffer *buffer,
+                      struct ring_buffer_per_cpu *cpu_buffer,
                       unsigned long length)
 {
         struct ring_buffer_event *event;
@@ -1492,6 +2082,21 @@ rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
 
         rb_start_commit(cpu_buffer);
 
+#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
+        /*
+         * Due to the ability to swap a cpu buffer from a buffer
+         * it is possible it was swapped before we committed.
+         * (committing stops a swap). We check for it here and
+         * if it happened, we have to fail the write.
+         */
+        barrier();
+        if (unlikely(ACCESS_ONCE(cpu_buffer->buffer) != buffer)) {
+                local_dec(&cpu_buffer->committing);
+                local_dec(&cpu_buffer->commits);
+                return NULL;
+        }
+#endif
+
         length = rb_calculate_event_length(length);
  again:
         /*
@@ -1652,7 +2257,7 @@ ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
         if (length > BUF_MAX_DATA_SIZE)
                 goto out;
 
-        event = rb_reserve_next_event(cpu_buffer, length);
+        event = rb_reserve_next_event(buffer, cpu_buffer, length);
         if (!event)
                 goto out;
 
@@ -1675,18 +2280,23 @@ ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
 }
 EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
 
-static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
+static void
+rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
                       struct ring_buffer_event *event)
 {
-        local_inc(&cpu_buffer->entries);
-
         /*
          * The event first in the commit queue updates the
          * time stamp.
          */
         if (rb_event_is_commit(cpu_buffer, event))
                 cpu_buffer->write_stamp += event->time_delta;
+}
 
+static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
+                      struct ring_buffer_event *event)
+{
+        local_inc(&cpu_buffer->entries);
+        rb_update_write_stamp(cpu_buffer, event);
         rb_end_commit(cpu_buffer);
 }
 
@@ -1733,32 +2343,57 @@ static inline void rb_event_discard(struct ring_buffer_event *event)
                 event->time_delta = 1;
 }
 
-/**
- * ring_buffer_event_discard - discard any event in the ring buffer
- * @event: the event to discard
- *
- * Sometimes a event that is in the ring buffer needs to be ignored.
- * This function lets the user discard an event in the ring buffer
- * and then that event will not be read later.
- *
- * Note, it is up to the user to be careful with this, and protect
- * against races. If the user discards an event that has been consumed
- * it is possible that it could corrupt the ring buffer.
+/*
+ * Decrement the entries to the page that an event is on.
+ * The event does not even need to exist, only the pointer
+ * to the page it is on. This may only be called before the commit
+ * takes place.
  */
-void ring_buffer_event_discard(struct ring_buffer_event *event)
+static inline void
+rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
+                   struct ring_buffer_event *event)
 {
-        rb_event_discard(event);
+        unsigned long addr = (unsigned long)event;
+        struct buffer_page *bpage = cpu_buffer->commit_page;
+        struct buffer_page *start;
+
+        addr &= PAGE_MASK;
+
+        /* Do the likely case first */
+        if (likely(bpage->page == (void *)addr)) {
+                local_dec(&bpage->entries);
+                return;
+        }
+
+        /*
+         * Because the commit page may be on the reader page we
+         * start with the next page and check the end loop there.
+         */
+        rb_inc_page(cpu_buffer, &bpage);
+        start = bpage;
+        do {
+                if (bpage->page == (void *)addr) {
+                        local_dec(&bpage->entries);
+                        return;
+                }
+                rb_inc_page(cpu_buffer, &bpage);
+        } while (bpage != start);
+
+        /* commit not part of this buffer?? */
+        RB_WARN_ON(cpu_buffer, 1);
 }
-EXPORT_SYMBOL_GPL(ring_buffer_event_discard);
 
 /**
  * ring_buffer_commit_discard - discard an event that has not been committed
  * @buffer: the ring buffer
  * @event: non committed event to discard
  *
- * This is similar to ring_buffer_event_discard but must only be
- * performed on an event that has not been committed yet. The difference
- * is that this will also try to free the event from the ring buffer
+ * Sometimes an event that is in the ring buffer needs to be ignored.
+ * This function lets the user discard an event in the ring buffer
+ * and then that event will not be read later.
+ *
+ * This function only works if it is called before the the item has been
+ * committed. It will try to free the event from the ring buffer
  * if another event has not been added behind it.
  *
  * If another event has been added behind it, it will set the event
@@ -1786,14 +2421,15 @@ void ring_buffer_discard_commit(struct ring_buffer *buffer,
          */
         RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
 
+        rb_decrement_entry(cpu_buffer, event);
         if (rb_try_to_discard(cpu_buffer, event))
                 goto out;
 
         /*
          * The commit is still visible by the reader, so we
-         * must increment entries.
+         * must still update the timestamp.
          */
-        local_inc(&cpu_buffer->entries);
+        rb_update_write_stamp(cpu_buffer, event);
  out:
         rb_end_commit(cpu_buffer);
 
@@ -1854,7 +2490,7 @@ int ring_buffer_write(struct ring_buffer *buffer,
         if (length > BUF_MAX_DATA_SIZE)
                 goto out;
 
-        event = rb_reserve_next_event(cpu_buffer, length);
+        event = rb_reserve_next_event(buffer, cpu_buffer, length);
         if (!event)
                 goto out;
 
@@ -1875,9 +2511,13 @@ EXPORT_SYMBOL_GPL(ring_buffer_write);
 static int rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
 {
         struct buffer_page *reader = cpu_buffer->reader_page;
-        struct buffer_page *head = cpu_buffer->head_page;
+        struct buffer_page *head = rb_set_head_page(cpu_buffer);
         struct buffer_page *commit = cpu_buffer->commit_page;
 
+        /* In case of error, head will be NULL */
+        if (unlikely(!head))
+                return 1;
+
         return reader->read == rb_page_commit(reader) &&
                 (commit == reader ||
                  (commit == head &&
@@ -1968,7 +2608,7 @@ unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
                 return 0;
 
         cpu_buffer = buffer->buffers[cpu];
-        ret = (local_read(&cpu_buffer->entries) - cpu_buffer->overrun)
+        ret = (local_read(&cpu_buffer->entries) - local_read(&cpu_buffer->overrun))
                 - cpu_buffer->read;
 
         return ret;
@@ -1989,33 +2629,13 @@ unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
                 return 0;
 
         cpu_buffer = buffer->buffers[cpu];
-        ret = cpu_buffer->overrun;
+        ret = local_read(&cpu_buffer->overrun);
 
         return ret;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
 
 /**
- * ring_buffer_nmi_dropped_cpu - get the number of nmis that were dropped
- * @buffer: The ring buffer
- * @cpu: The per CPU buffer to get the number of overruns from
- */
-unsigned long ring_buffer_nmi_dropped_cpu(struct ring_buffer *buffer, int cpu)
-{
-        struct ring_buffer_per_cpu *cpu_buffer;
-        unsigned long ret;
-
-        if (!cpumask_test_cpu(cpu, buffer->cpumask))
-                return 0;
-
-        cpu_buffer = buffer->buffers[cpu];
-        ret = cpu_buffer->nmi_dropped;
-
-        return ret;
-}
-EXPORT_SYMBOL_GPL(ring_buffer_nmi_dropped_cpu);
-
-/**
  * ring_buffer_commit_overrun_cpu - get the number of overruns caused by commits
  * @buffer: The ring buffer
  * @cpu: The per CPU buffer to get the number of overruns from
@@ -2030,7 +2650,7 @@ ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
                 return 0;
 
         cpu_buffer = buffer->buffers[cpu];
-        ret = cpu_buffer->commit_overrun;
+        ret = local_read(&cpu_buffer->commit_overrun);
 
         return ret;
 }
@@ -2053,7 +2673,7 @@ unsigned long ring_buffer_entries(struct ring_buffer *buffer)
         for_each_buffer_cpu(buffer, cpu) {
                 cpu_buffer = buffer->buffers[cpu];
                 entries += (local_read(&cpu_buffer->entries) -
-                            cpu_buffer->overrun) - cpu_buffer->read;
+                            local_read(&cpu_buffer->overrun)) - cpu_buffer->read;
         }
 
         return entries;
@@ -2076,7 +2696,7 @@ unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
         /* if you care about this being correct, lock the buffer */
         for_each_buffer_cpu(buffer, cpu) {
                 cpu_buffer = buffer->buffers[cpu];
-                overruns += cpu_buffer->overrun;
+                overruns += local_read(&cpu_buffer->overrun);
         }
 
         return overruns;
@@ -2089,8 +2709,10 @@ static void rb_iter_reset(struct ring_buffer_iter *iter)
 
         /* Iterator usage is expected to have record disabled */
         if (list_empty(&cpu_buffer->reader_page->list)) {
-                iter->head_page = cpu_buffer->head_page;
-                iter->head = cpu_buffer->head_page->read;
+                iter->head_page = rb_set_head_page(cpu_buffer);
+                if (unlikely(!iter->head_page))
+                        return;
+                iter->head = iter->head_page->read;
         } else {
                 iter->head_page = cpu_buffer->reader_page;
                 iter->head = cpu_buffer->reader_page->read;
@@ -2207,6 +2829,7 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
         struct buffer_page *reader = NULL;
         unsigned long flags;
         int nr_loops = 0;
+        int ret;
 
         local_irq_save(flags);
         __raw_spin_lock(&cpu_buffer->lock);
@@ -2240,30 +2863,56 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
                 goto out;
 
         /*
-         * Splice the empty reader page into the list around the head.
          * Reset the reader page to size zero.
          */
+        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);
 
-        reader = cpu_buffer->head_page;
+ spin:
+        /*
+         * Splice the empty reader page into the list around the head.
+         */
+        reader = rb_set_head_page(cpu_buffer);
         cpu_buffer->reader_page->list.next = reader->list.next;
         cpu_buffer->reader_page->list.prev = 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);
+        /*
+         * 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;
 
-        /* Make the reader page now replace the head */
-        reader->list.prev->next = &cpu_buffer->reader_page->list;
-        reader->list.next->prev = &cpu_buffer->reader_page->list;
+        /* The reader page will be pointing to the new head */
+        rb_set_list_to_head(cpu_buffer, &cpu_buffer->reader_page->list);
 
         /*
-         * If the tail is on the reader, then we must set the head
-         * to the inserted page, otherwise we set it one before.
+         * Here's the tricky part.
+         *
+         * We need to move the pointer past the header page.
+         * But we can only do that if a writer is not currently
+         * moving it. The page before the header page has the
+         * flag bit '1' set if it is pointing to the page we want.
+         * but if the writer is in the process of moving it
+         * than it will be '2' or already moved '0'.
          */
-        cpu_buffer->head_page = cpu_buffer->reader_page;
 
-        if (cpu_buffer->commit_page != reader)
-                rb_inc_page(cpu_buffer, &cpu_buffer->head_page);
+        ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
+
+        /*
+         * If we did not convert it, then we must try again.
+         */
+        if (!ret)
+                goto spin;
+
+        /*
+         * Yeah! We succeeded in replacing the page.
+         *
+         * Now make the new head point back to the reader page.
+         */
+        reader->list.next->prev = &cpu_buffer->reader_page->list;
+        rb_inc_page(cpu_buffer, &cpu_buffer->head_page);
 
         /* Finally update the reader page to the new head */
         cpu_buffer->reader_page = reader;
@@ -2292,8 +2941,7 @@ static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
 
         event = rb_reader_event(cpu_buffer);
 
-        if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX
-                        || rb_discarded_event(event))
+        if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
                 cpu_buffer->read++;
 
         rb_update_read_stamp(cpu_buffer, event);
@@ -2347,15 +2995,12 @@ static void rb_advance_iter(struct ring_buffer_iter *iter)
 }
 
 static struct ring_buffer_event *
-rb_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
+rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts)
 {
-        struct ring_buffer_per_cpu *cpu_buffer;
         struct ring_buffer_event *event;
         struct buffer_page *reader;
         int nr_loops = 0;
 
-        cpu_buffer = buffer->buffers[cpu];
-
  again:
         /*
          * We repeat when a timestamp is encountered. It is possible
@@ -2399,7 +3044,7 @@ rb_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
         case RINGBUF_TYPE_DATA:
                 if (ts) {
                         *ts = cpu_buffer->read_stamp + event->time_delta;
-                        ring_buffer_normalize_time_stamp(buffer,
+                        ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
                                                          cpu_buffer->cpu, ts);
                 }
                 return event;
@@ -2518,17 +3163,15 @@ ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
         local_irq_save(flags);
         if (dolock)
                 spin_lock(&cpu_buffer->reader_lock);
-        event = rb_buffer_peek(buffer, cpu, ts);
+        event = rb_buffer_peek(cpu_buffer, ts);
         if (event && event->type_len == RINGBUF_TYPE_PADDING)
                 rb_advance_reader(cpu_buffer);
         if (dolock)
                 spin_unlock(&cpu_buffer->reader_lock);
         local_irq_restore(flags);
 
-        if (event && event->type_len == RINGBUF_TYPE_PADDING) {
-                cpu_relax();
+        if (event && event->type_len == RINGBUF_TYPE_PADDING)
                 goto again;
-        }
 
         return event;
 }
@@ -2553,10 +3196,8 @@ ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
         event = rb_iter_peek(iter, ts);
         spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
-        if (event && event->type_len == RINGBUF_TYPE_PADDING) {
-                cpu_relax();
+        if (event && event->type_len == RINGBUF_TYPE_PADDING)
                 goto again;
-        }
 
         return event;
 }
@@ -2591,7 +3232,7 @@ ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts)
         if (dolock)
                 spin_lock(&cpu_buffer->reader_lock);
 
-        event = rb_buffer_peek(buffer, cpu, ts);
+        event = rb_buffer_peek(cpu_buffer, ts);
         if (event)
                 rb_advance_reader(cpu_buffer);
 
@@ -2602,10 +3243,8 @@ ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts)
  out:
         preempt_enable();
 
-        if (event && event->type_len == RINGBUF_TYPE_PADDING) {
-                cpu_relax();
+        if (event && event->type_len == RINGBUF_TYPE_PADDING)
                 goto again;
-        }
 
         return event;
 }
@@ -2685,21 +3324,19 @@ ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
         struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
         unsigned long flags;
 
- again:
         spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+ again:
         event = rb_iter_peek(iter, ts);
         if (!event)
                 goto out;
 
+        if (event->type_len == RINGBUF_TYPE_PADDING)
+                goto again;
+
         rb_advance_iter(iter);
  out:
         spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
-        if (event && event->type_len == RINGBUF_TYPE_PADDING) {
-                cpu_relax();
-                goto again;
-        }
-
         return event;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_read);
@@ -2717,8 +3354,10 @@ EXPORT_SYMBOL_GPL(ring_buffer_size);
 static void
 rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
 {
+        rb_head_page_deactivate(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);
@@ -2734,16 +3373,17 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
         local_set(&cpu_buffer->reader_page->page->commit, 0);
         cpu_buffer->reader_page->read = 0;
 
-        cpu_buffer->nmi_dropped = 0;
-        cpu_buffer->commit_overrun = 0;
-        cpu_buffer->overrun = 0;
-        cpu_buffer->read = 0;
+        local_set(&cpu_buffer->commit_overrun, 0);
+        local_set(&cpu_buffer->overrun, 0);
         local_set(&cpu_buffer->entries, 0);
         local_set(&cpu_buffer->committing, 0);
         local_set(&cpu_buffer->commits, 0);
+        cpu_buffer->read = 0;
 
         cpu_buffer->write_stamp = 0;
         cpu_buffer->read_stamp = 0;
+
+        rb_head_page_activate(cpu_buffer);
 }
 
 /**
@@ -2763,12 +3403,16 @@ void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
 
         spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 
+        if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
+                goto out;
+
         __raw_spin_lock(&cpu_buffer->lock);
 
         rb_reset_cpu(cpu_buffer);
 
         __raw_spin_unlock(&cpu_buffer->lock);
 
+ out:
         spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
         atomic_dec(&cpu_buffer->record_disabled);
@@ -2851,6 +3495,7 @@ int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
 }
 EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
 
+#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
 /**
  * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
  * @buffer_a: One buffer to swap with
@@ -2905,20 +3550,28 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
         atomic_inc(&cpu_buffer_a->record_disabled);
         atomic_inc(&cpu_buffer_b->record_disabled);
 
+        ret = -EBUSY;
+        if (local_read(&cpu_buffer_a->committing))
+                goto out_dec;
+        if (local_read(&cpu_buffer_b->committing))
+                goto out_dec;
+
         buffer_a->buffers[cpu] = cpu_buffer_b;
         buffer_b->buffers[cpu] = cpu_buffer_a;
 
         cpu_buffer_b->buffer = buffer_a;
         cpu_buffer_a->buffer = buffer_b;
 
+        ret = 0;
+
+out_dec:
         atomic_dec(&cpu_buffer_a->record_disabled);
         atomic_dec(&cpu_buffer_b->record_disabled);
-
-        ret = 0;
 out:
         return ret;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
+#endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
 
 /**
  * ring_buffer_alloc_read_page - allocate a page to read from buffer
@@ -3091,7 +3744,7 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
                 read = 0;
         } else {
                 /* update the entry counter */
-                cpu_buffer->read += local_read(&reader->entries);
+                cpu_buffer->read += rb_page_entries(reader);
 
                 /* swap the pages */
                 rb_init_page(bpage);