linux-kernel - Re: [PATCH 07/13] tracing/kdb: remove redundant checking

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Date:	Mon, 11 Mar 2013 23:54:00 +0800
From:	Jovi Zhang <bookjovi@...il.com>
To:	Jason Wessel <jason.wessel@...driver.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 07/13] tracing/kdb: remove redundant checking

On Mon, Mar 11, 2013 at 10:46 PM, Jason Wessel
<jason.wessel@...driver.com> wrote:
> On 03/11/2013 09:09 AM, Steven Rostedt wrote:
>> This is Jason's code.
>>
>> Jason, please give an Ack or Nack.
>>
>> Thanks,
>>
>> -- Steve
>>
>>
>> On Mon, 2013-03-11 at 15:13 +0800, zhangwei(Jovi) wrote:
>>> trace_empty is checking in while-loop, so the previous checking
>>> is totally redundant, and more worse, the first trace entry is losted.
>>>
>>> so remove it.
>>>
>>> Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@...wei.com>
>>> ---
>>>  kernel/trace/trace_kdb.c |    3 +--
>>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>>
>>> diff --git a/kernel/trace/trace_kdb.c b/kernel/trace/trace_kdb.c
>>> index 3c5c5df..6489b2e 100644
>>> --- a/kernel/trace/trace_kdb.c
>>> +++ b/kernel/trace/trace_kdb.c
>>> @@ -57,8 +57,7 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file)
>>>              ring_buffer_read_start(iter.buffer_iter[cpu_file]);
>>>              tracing_iter_reset(&iter, cpu_file);
>>>      }
>>> -    if (!trace_empty(&iter))
>>> -            trace_find_next_entry_inc(&iter);
>>> +
>>>      while (!trace_empty(&iter)) {
>>>              if (!cnt)
>>>                      kdb_printf("---------------------------------\n");
>>
>
>
> This was just a copy of part of the logic used for printing the information in a similar manner to what you get when you cat the trace buffer to obtain the human readable version.
>
> May I ask how you tested it though?
No, just watch the code, and that part looks weird.

kdb_ftdump seems copied from ftrace_dump function, it have similar
functionality,
can we have some way to unify these two function into one common function?
this at least can save trace_iterator static memory ~8k+. (I'm not
sure this can work or not)

>
> As far as I know the patch I sent Stephen quite a while ago got lost and the mainline version of the "ftdump" doesn't actually work.
>
> Example:
> [0]kdb> ftdump
> Dumping ftrace buffer:
> 3BUG: sleeping function called from invalid context at /space/jw/git/kgdb/linux-2.6-kgdb/mm/slub.c:925
> 3in_atomic(): 1, irqs_disabled(): 1, pid: 81, name: sh
> Pid: 81, comm: sh Not tainted 3.9.0-rc1-WR4.3.0.0_standard+ #568
> Call Trace:
>  <#DB>  [<ffffffff81069ffe>] __might_sleep+0xde/0x100
>  [<ffffffff8112611b>] kmem_cache_alloc_trace+0xdb/0x170
>  [<ffffffff810c01bd>] ring_buffer_read_prepare+0x4d/0x70
>  [<ffffffff810d4d28>] kdb_ftdump+0x1e8/0x410
>  [<ffffffff810a9a89>] kdb_parse+0x209/0x690
>  [<ffffffff810aad0c>] kdb_main_loop+0x67c/0x8c0
>  [<ffffffff810ad4b3>] kdb_stub+0x1d3/0x420
>  [<ffffffff8104ccfd>] ? __send_signal+0x1ad/0x3e0
>  [<ffffffff810a33be>] kgdb_cpu_enter+0x27e/0x590
>  [<ffffffff810a3981>] kgdb_handle_exception+0x161/0x1c0
>  [<ffffffff81027cf1>] __kgdb_notify+0x31/0xe0
>  [<ffffffff81027e10>] kgdb_ll_trap+0x40/0x50
>  [<ffffffff81002e12>] do_int3+0x52/0x130
>  [<ffffffff81674345>] int3+0x25/0x40
>  [<ffffffff810a2be2>] ? sysrq_handle_dbg+0x32/0x60
>  <<EOE>>  [<ffffffff813e1e69>] __handle_sysrq+0x129/0x190
>
>
> I think we need to actually empirically prove the code change is right or wrong before merging it, as well as cleaning up the change log slightly.
>
> I'll go hunt down the patch the fixes the oops first.
>
> Cheers,
> Jason.
> --
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