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

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

On 2017/01/12 03:49PM, Qu Wenruo 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?

Yes, use -g option with 'perf record'. In fact, I don't think you even 
need to add a new tracepoint - you should be able to use kprobes (perf 
probe) at structure allocation/free points.

A more efficient way would probably use a eBPF program with stackmaps to 
track the stack traces.

- Naveen