1 files changed, 38 insertions, 63 deletions

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 9c2ddfbf4525..e8b168af135b 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -12,40 +12,10 @@
 #include <linux/perf_event.h>
 #include <linux/vmalloc.h>
 #include <linux/slab.h>
+#include <linux/circ_buf.h>
 
 #include "internal.h"
 
-static bool perf_output_space(struct ring_buffer *rb, unsigned long tail,
-                              unsigned long offset, unsigned long head)
-{
-        unsigned long sz = perf_data_size(rb);
-        unsigned long mask = sz - 1;
-
-        /*
-         * check if user-writable
-         * overwrite : over-write its own tail
-         * !overwrite: buffer possibly drops events.
-         */
-        if (rb->overwrite)
-                return true;
-
-        /*
-         * verify that payload is not bigger than buffer
-         * otherwise masking logic may fail to detect
-         * the "not enough space" condition
-         */
-        if ((head - offset) > sz)
-                return false;
-
-        offset = (offset - tail) & mask;
-        head   = (head   - tail) & mask;
-
-        if ((int)(head - offset) < 0)
-                return false;
-
-        return true;
-}
-
 static void perf_output_wakeup(struct perf_output_handle *handle)
 {
         atomic_set(&handle->rb->poll, POLL_IN);
@@ -115,8 +85,8 @@ again:
         rb->user_page->data_head = head;
 
         /*
-         * Now check if we missed an update, rely on the (compiler)
-         * barrier in atomic_dec_and_test() to re-read rb->head.
+         * Now check if we missed an update -- rely on previous implied
+         * compiler barriers to force a re-read.
          */
         if (unlikely(head != local_read(&rb->head))) {
                 local_inc(&rb->nest);
@@ -135,8 +105,7 @@ int perf_output_begin(struct perf_output_handle *handle,
 {
         struct ring_buffer *rb;
         unsigned long tail, offset, head;
-        int have_lost;
-        struct perf_sample_data sample_data;
+        int have_lost, page_shift;
         struct {
                 struct perf_event_header header;
                 u64                      id;
@@ -151,57 +120,63 @@ int perf_output_begin(struct perf_output_handle *handle,
                 event = event->parent;
 
         rb = rcu_dereference(event->rb);
-        if (!rb)
+        if (unlikely(!rb))
                 goto out;
 
-        handle->rb      = rb;
-        handle->event   = event;
-
-        if (!rb->nr_pages)
+        if (unlikely(!rb->nr_pages))
                 goto out;
 
+        handle->rb    = rb;
+        handle->event = event;
+
         have_lost = local_read(&rb->lost);
-        if (have_lost) {
-                lost_event.header.size = sizeof(lost_event);
-                perf_event_header__init_id(&lost_event.header, &sample_data,
-                                           event);
-                size += lost_event.header.size;
+        if (unlikely(have_lost)) {
+                size += sizeof(lost_event);
+                if (event->attr.sample_id_all)
+                        size += event->id_header_size;
         }
 
         perf_output_get_handle(handle);
 
         do {
-                /*
-                 * Userspace could choose to issue a mb() before updating the
-                 * tail pointer. So that all reads will be completed before the
-                 * write is issued.
-                 *
-                 * See perf_output_put_handle().
-                 */
                 tail = ACCESS_ONCE(rb->user_page->data_tail);
-                smp_mb();
                 offset = head = local_read(&rb->head);
-                head += size;
-                if (unlikely(!perf_output_space(rb, tail, offset, head)))
+                if (!rb->overwrite &&
+                    unlikely(CIRC_SPACE(head, tail, perf_data_size(rb)) < size))
                         goto fail;
+                head += size;
         } while (local_cmpxchg(&rb->head, offset, head) != offset);
 
-        if (head - local_read(&rb->wakeup) > rb->watermark)
+        /*
+         * Separate the userpage->tail read from the data stores below.
+         * Matches the MB userspace SHOULD issue after reading the data
+         * and before storing the new tail position.
+         *
+         * See perf_output_put_handle().
+         */
+        smp_mb();
+
+        if (unlikely(head - local_read(&rb->wakeup) > rb->watermark))
                 local_add(rb->watermark, &rb->wakeup);
 
-        handle->page = offset >> (PAGE_SHIFT + page_order(rb));
-        handle->page &= rb->nr_pages - 1;
-        handle->size = offset & ((PAGE_SIZE << page_order(rb)) - 1);
-        handle->addr = rb->data_pages[handle->page];
-        handle->addr += handle->size;
-        handle->size = (PAGE_SIZE << page_order(rb)) - handle->size;
+        page_shift = PAGE_SHIFT + page_order(rb);
 
-        if (have_lost) {
+        handle->page = (offset >> page_shift) & (rb->nr_pages - 1);
+        offset &= (1UL << page_shift) - 1;
+        handle->addr = rb->data_pages[handle->page] + offset;
+        handle->size = (1UL << page_shift) - offset;
+
+        if (unlikely(have_lost)) {
+                struct perf_sample_data sample_data;
+
+                lost_event.header.size = sizeof(lost_event);
                 lost_event.header.type = PERF_RECORD_LOST;
                 lost_event.header.misc = 0;
                 lost_event.id          = event->id;
                 lost_event.lost        = local_xchg(&rb->lost, 0);
 
+                perf_event_header__init_id(&lost_event.header,
+                                           &sample_data, event);
                 perf_output_put(handle, lost_event);
                 perf_event__output_id_sample(event, handle, &sample_data);
         }