Re: Is it possible to trace events and its call stack?

[Masami Hiramatsu <mhiramat@kernel.org>]

On Thu, 12 Jan 2017 15:49:08 +0800
Qu Wenruo <quwenruo@cn.fujitsu.com> wrote:

> Hi,
> 
> Is it possible to use perf/ftrace to trace events and its call stack?
> 
> [Background]
> It's one structure in btrfs, btrfs_bio, I'm tracing for.
> That structure is allocated and free somewhat frequently, and its size 
> is not fixed, so no SLAB/SLUB cache is used.
> 
> I added trace events(or trace points, anyway, just in 
> include/trace/events/btrfs.h) to trace the allocation and freeing.
> Which will output the pointer address of that structure, so I can pair 
> them, alone with other info.
> 
> Things went well until, I found some structures are allocated but not 
> freed. (no corresponding trace point is triggered for given address).
> 
> It's possible that btrfs just forget to free it, or btrfs is just 
> holding it for some purpose.
> So kernel memleak detector won't catch the later one.
> 
> That's to say along with the tracepoint data, I still need the call 
> stack of each calling, to determine the code who leak or hold the pointer.
> 
> Is it possible to do it using perf or ftrace?

If you are using ftrace, yes, you can enable stacktrace for each
events by setting stacktrace event trigger as below;

echo stacktrace > events/btrfs/<your event>/trigger

Then ftrace will show the stacktrace data.
See /sys/kernel/debug/tracing/README for more details. :)

Thank you,

> 
> Thanks,
> Qu
> 
> 
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-- 
Masami Hiramatsu <mhiramat@kernel.org>