Re: [PATCH] ath10k: change len of trace_ath10k_log_dbg_dump for large buffer size

From: Wen Gong <wgong@codeaurora.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Brian Norris <briannorris@chromium.org>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	ath10k <ath10k@lists.infradead.org>
Subject: Re: [PATCH] ath10k: change len of trace_ath10k_log_dbg_dump for large buffer size
Date: Wed, 10 Feb 2021 10:01:57 +0800	[thread overview]
Message-ID: <9b479a88331dbf969f07708eabe53d14@codeaurora.org> (raw)
In-Reply-To: <20210209163431.11133472@gandalf.local.home>

On 2021-02-10 05:34, Steven Rostedt wrote:
> On Tue, 9 Feb 2021 14:55:31 -0500
> Steven Rostedt <rostedt@goodmis.org> wrote:
> 
>> > [for-next][PATCH 2/2] tracing: Use temp buffer when filtering events
>> > https://lore.kernel.org/lkml/f16b14066317f6a926b6636df6974966@codeaurora.org/
>> 
>> Note, that is only used when filtering happens, which doesn't appear 
>> to be
>> the case here.
> 
> I was basing this off of the original commands, but the stack dump says
> otherwise. But it should still work.
> 
>> 
>> >
>> > It seems like we should still try to get that fixed somehow, even if
>> > the below change is fine on its own (it probably doesn't make sense to
>> > such a large amount of data via tracepoints). It would be unfortunate
>> > for next poor soul to hit the same issues, just because they wanted to
>> > dump a few KB.
>> 
>> Yeah, it was a design decision to cap the max size of events to just 
>> under
>> PAGE_SIZE. The ring buffer is broken up into pages (for zero copy
>> transfers to file systems and the network). Thus, no event is allowed 
>> to be
>> bigger than a page (and actually a bit smaller)
>> 
>> That said, it shouldn't have crashed, it should have just failed to 
>> record.
>> 
>> I'll test it out and see why it crashed.
> 
> Looking at the original report, I see:
> 
>  CPU: 1 PID: 141 Comm: kworker/u16:1 Not tainted 4.19.139 #162
> 
> Does this still crash on the latest kernel?
> 
> -- Steve
Not tested with latest kernel.
The reason is below which I said in 
https://lore.kernel.org/lkml/b504b3d7e989cae108669a0cd3072454@codeaurora.org/

the per cpu buffer seems it is initilized in 
trace_buffered_event_enable,
it is only 1 page size as below:
void trace_buffered_event_enable(void)
{
...
	for_each_tracing_cpu(cpu) {
		page = alloc_pages_node(cpu_to_node(cpu),
					GFP_KERNEL | __GFP_NORETRY, 0);
If the size of buffer to trace is more than 1 page, such as 46680, then
it trigger kernel crash/panic in my case while run trace-cmd.
After debugging, the trace_file->flags in
trace_event_buffer_lock_reserve is 0x40b while run trace-cmd, and it is
0x403 while collecting ftrace log.

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