Messages in this thread Patch in this message | | | Date | Fri, 17 Jul 2015 10:32:15 -0400 | From | Steven Rostedt <> | Subject | Re: [RFC PATCH v4 1/3] tracing/events: Fix wrong sample output by storing array length instead of size |
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On Fri, 10 Jul 2015 10:03:05 +0000 He Kuang <hekuang@huawei.com> wrote:
> The output result of trace_foo_bar event in traceevent samples is > wrong. This problem can be reproduced as following: > > (Build kernel with SAMPLE_TRACE_EVENTS=m) > > $ insmod trace-events-sample.ko > > $ echo 1 > /sys/kernel/debug/tracing/events/sample-trace/foo_bar/enable > > $ cat /sys/kernel/debug/tracing/trace > > event-sample-980 [000] .... 43.649559: foo_bar: foo hello 21 0x15 > BIT1|BIT3|0x10 {0x1,0x6f6f6e53,0xff007970,0xffffffff} Snoopy > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > The array length is not right, should be {0x1}. > (ffffffff,ffffffff) > > event-sample-980 [000] .... 44.653827: foo_bar: foo hello 22 0x16 > BIT2|BIT3|0x10 > {0x1,0x2,0x646e6147,0x666c61,0xffffffff,0xffffffff,0x750aeffe,0x7} > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > The array length is not right, should be {0x1,0x2}. > Gandalf (ffffffff,ffffffff) > > The event defined in samples/trace_events/trace-events-sample.h uses > this helper function to output dynamic list: > > __print_array(__get_dynamic_array(list), > __get_dynamic_array_len(list), > sizeof(int)) > > Currently, __get_dynamic_array_len() returns the total size of the > array instead of the number of items by referencing the high 16 bits > of entry->data_loc_##item. The element size for calculating the number > of items can not be fetched by referencing fields from __entry, so > macro __get_dynamic_array_len can not return the expected value. > > This patch stores array item number instead of the total size in > entry->__data_loc_##item, and makes __get_dynamic_array_len get the > right value directly. Because the function __get_bitmask() is affected > by this change, __bitmask_size is assigned to the array len by > multiplied bitmask type size. > > After this patch: > > event-sample-993 [000] .... 692.348562: foo_bar: foo hello 201 > 0xc9 BIT1|BIT4|0xc0 {0x1} Snoopy (ffffffff,ffffffff) > ^^^^^ > Array length fixed. > > event-sample-993 [000] .... 693.349276: foo_bar: foo hello 202 > 0xca BIT2|BIT4|0xc0 {0x1,0x2} Gandalf (ffffffff,ffffffff) > ^^^^^^^^^ > Array length fixed. > > Signed-off-by: He Kuang <hekuang@huawei.com> > --- > include/trace/trace_events.h | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h > index 43be3b0..5abe027 100644 > --- a/include/trace/trace_events.h > +++ b/include/trace/trace_events.h > @@ -257,7 +257,8 @@ TRACE_MAKE_SYSTEM_STR(); > ({ \ > void *__bitmask = __get_dynamic_array(field); \ > unsigned int __bitmask_size; \ > - __bitmask_size = __get_dynamic_array_len(field); \ > + __bitmask_size = (__get_dynamic_array_len(field) * \ > + sizeof(unsigned long)); \ > trace_print_bitmask_seq(p, __bitmask, __bitmask_size); \ > }) > > @@ -453,7 +454,7 @@ trace_event_define_fields_##call(struct trace_event_call *event_call) \ > __item_length = (len) * sizeof(type); \ > __data_offsets->item = __data_size + \ > offsetof(typeof(*entry), __data); \ > - __data_offsets->item |= __item_length << 16; \ > + __data_offsets->item |= (len) << 16; \
This change affects all callers of dymanic_array, not just bitmasks.
> __data_size += __item_length; > > #undef __string
BTW, if I revert commit ac01ce1410fc2 "tracing: Make ftrace_print_array_seq compute buf_len" it works again.
I'm going to look into this some more, and maybe the answer is to go back and just pass in buffer length here. I can't see what was broken before that change.
-- Steve
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