Messages in this thread Patch in this message | | | Subject | [PATCH][GIT PULL][v2.6.37] ring_buffer: Off-by-one and duplicate events in ring_buffer_read_page | From | Steven Rostedt <> | Date | Thu, 23 Dec 2010 16:34:49 -0500 |
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Ingo,
Please pull the latest tip/perf/urgent tree, which can be found at:
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git tip/perf/urgent
David Sharp (1): ring_buffer: Off-by-one and duplicate events in ring_buffer_read_page
---- kernel/trace/ring_buffer.c | 9 ++++++++- 1 files changed, 8 insertions(+), 1 deletions(-) --------------------------- commit e1e359273576ee8fe27021356b064c772ed29af3 Author: David Sharp <dhsharp@google.com> Date: Wed Dec 22 16:38:24 2010 -0800
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>
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 9ed509a..bd1c35a 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, /* Need to copy one event at a time */ do { + /* We need the size of one event, because + * rb_advance_reader only advances by one event, + * whereas rb_event_ts_length may include the size of + * one or two events. + * We have already ensured there's enough space if this + * is a time extend. */ + size = rb_event_length(event); memcpy(bpage->data + pos, rpage->data + rpos, size); len -= size; @@ -3867,7 +3874,7 @@ int ring_buffer_read_page(struct ring_buffer *buffer, event = rb_reader_event(cpu_buffer); /* Always keep the time extend and data together */ size = rb_event_ts_length(event); - } while (len > size); + } while (len >= size); /* update bpage */ local_set(&bpage->commit, pos);
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