aboutsummaryrefslogtreecommitdiffstats
path: root/kernel
diff options
context:
space:
mode:
authorDavid Sharp <dhsharp@google.com>2010-12-22 19:38:24 -0500
committerSteven Rostedt <rostedt@goodmis.org>2010-12-23 12:09:30 -0500
commite1e359273576ee8fe27021356b064c772ed29af3 (patch)
treec1a8aa53fb3044162851aa7a7bc9d72f710232d1 /kernel
parent2ce494a3dac331fdbb2590e5fa0598956dd21b8b (diff)
ring_buffer: Off-by-one and duplicate events in ring_buffer_read_page
Fix two related problems in the event-copying loop of ring_buffer_read_page. The loop condition for copying events is off-by-one. "len" is the remaining space in the caller-supplied page. "size" is the size of the next event (or two events). If len == size, then there is just enough space for the next event. size was set to rb_event_ts_length, which may include the size of two events if the first event is a time-extend, in order to assure time- extends are kept together with the event after it. However, rb_advance_reader always advances by one event. This would result in the event after any time-extend being duplicated. Instead, get the size of a single event for the memcpy, but use rb_event_ts_length for the loop condition. Signed-off-by: David Sharp <dhsharp@google.com> LKML-Reference: <1293064704-8101-1-git-send-email-dhsharp@google.com> LKML-Reference: <AANLkTin7nLrRPc9qGjdjHbeVDDWiJjAiYyb-L=gH85bx@mail.gmail.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/trace/ring_buffer.c9
1 files changed, 8 insertions, 1 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 9ed509a015d8..bd1c35a4fbcc 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3853,6 +3853,13 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
3853 3853
3854 /* Need to copy one event at a time */ 3854 /* Need to copy one event at a time */
3855 do { 3855 do {
3856 /* We need the size of one event, because
3857 * rb_advance_reader only advances by one event,
3858 * whereas rb_event_ts_length may include the size of
3859 * one or two events.
3860 * We have already ensured there's enough space if this
3861 * is a time extend. */
3862 size = rb_event_length(event);
3856 memcpy(bpage->data + pos, rpage->data + rpos, size); 3863 memcpy(bpage->data + pos, rpage->data + rpos, size);
3857 3864
3858 len -= size; 3865 len -= size;
@@ -3867,7 +3874,7 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
3867 event = rb_reader_event(cpu_buffer); 3874 event = rb_reader_event(cpu_buffer);
3868 /* Always keep the time extend and data together */ 3875 /* Always keep the time extend and data together */
3869 size = rb_event_ts_length(event); 3876 size = rb_event_ts_length(event);
3870 } while (len > size); 3877 } while (len >= size);
3871 3878
3872 /* update bpage */ 3879 /* update bpage */
3873 local_set(&bpage->commit, pos); 3880 local_set(&bpage->commit, pos);