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-rw-r--r--kernel/events/internal.h2
-rw-r--r--kernel/events/ring_buffer.c22
2 files changed, 19 insertions, 5 deletions
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index d56a64c99a8b..eb675c4d59df 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -16,7 +16,7 @@ struct ring_buffer {
int page_order; /* allocation order */
#endif
int nr_pages; /* nr of data pages */
- int writable; /* are we writable */
+ int overwrite; /* can overwrite itself */
atomic_t poll; /* POLL_ for wakeups */
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 23cb34ff3973..97fddb09762b 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -18,12 +18,24 @@
static bool perf_output_space(struct ring_buffer *rb, unsigned long tail,
unsigned long offset, unsigned long head)
{
- unsigned long mask;
+ unsigned long sz = perf_data_size(rb);
+ unsigned long mask = sz - 1;
- if (!rb->writable)
+ /*
+ * check if user-writable
+ * overwrite : over-write its own tail
+ * !overwrite: buffer possibly drops events.
+ */
+ if (rb->overwrite)
return true;
- mask = perf_data_size(rb) - 1;
+ /*
+ * 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;
@@ -212,7 +224,9 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
rb->watermark = max_size / 2;
if (flags & RING_BUFFER_WRITABLE)
- rb->writable = 1;
+ rb->overwrite = 0;
+ else
+ rb->overwrite = 1;
atomic_set(&rb->refcount, 1);