#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);
goto out;
/*
- * Publish the known good head. Rely on the full barrier implied
- * by atomic_dec_and_test() order the rb->head read and this
- * write.
+ * Since the mmap() consumer (userspace) can run on a different CPU:
+ *
+ * kernel user
+ *
+ * READ ->data_tail READ ->data_head
+ * smp_mb() (A) smp_rmb() (C)
+ * WRITE $data READ $data
+ * smp_wmb() (B) smp_mb() (D)
+ * STORE ->data_head WRITE ->data_tail
+ *
+ * Where A pairs with D, and B pairs with C.
+ *
+ * I don't think A needs to be a full barrier because we won't in fact
+ * write data until we see the store from userspace. So we simply don't
+ * issue the data WRITE until we observe it. Be conservative for now.
+ *
+ * OTOH, D needs to be a full barrier since it separates the data READ
+ * from the tail WRITE.
+ *
+ * For B a WMB is sufficient since it separates two WRITEs, and for C
+ * an RMB is sufficient since it separates two READs.
+ *
+ * See perf_output_begin().
*/
+ smp_wmb();
rb->user_page->data_head = head;
/*
{
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;
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.
- */
tail = ACCESS_ONCE(rb->user_page->data_tail);
- smp_rmb();
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);
}
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