Re: [for-next][PATCH 2/2] tracing: Use temp buffer when filtering events

[Steven Rostedt]

On Fri, 28 Aug 2020 15:53:06 +0800
Wen Gong <wgong@xxxxxxxxxxxxxx> wrote:

> this patch commit id is : 0fc1b09ff1ff404ddf753f5ffa5cd0adc8fdcdc9 which 
> has upstream.
> 
> how much size is 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.
> 
> Is it have any operation to disable this patch dynamically?

It shouldn't be disabled, this is a bug that needs to be fixed.

Also, if an event is more than a page, it wont be saved in the ftrace
ring buffer, as events are limited by page size minus the headers.

-- Steve