On Wed, Dec 09, 2015 at 10:41:38AM -0300, Arnaldo Carvalho de Melo wrote: > Em Wed, Dec 09, 2015 at 11:10:48AM +0900, Masami Hiramatsu escreveu: > > Hi Arnaldo, > > > > Here is a series of patches for perf refcnt debugger and > > some fixes. > > > > In this series I've replaced all atomic reference counters > > with the refcnt interface, including dso, map, map_groups, > > thread, cpu_map, comm_str, cgroup_sel, thread_map, and > > perf_mmap. > > > > refcnt debugger (or refcnt leak checker) > > =============== > > > > At first, note that this change doesn't affect any compiled > > code unless building with REFCNT_DEBUG=1 (see macros in > > refcnt.h). So, this feature is only enabled in the debug binary. > > But before releasing, we can ensure that all objects are safely > > reclaimed before exit in -rc phase. > > That helps and is finding bugs and is really great stuff, thank you! > > But I wonder if we couldn't get the same results on an unmodified binary > by using things like 'perf probe', the BPF code we're introducing, have > you thought about this possibility? > > I.e. trying to use 'perf probe' to do this would help in using the same > technique in other code bases where we can't change the sources, etc. > > For perf we could perhaps use a 'noinline' on the __get/__put > operations, so that we could have the right places to hook using > uprobes, other codebases would have to rely in the 'perf probe' > infrastructure that knows where inlines were expanded, etc. > > Such a toold could work like: > > perf dbgrefcnt ~/bin/perf thread > > And it would look up thread__get and thread__put(), create an eBPF map > where to store the needed tracking data structures, and use the same > techniques you used, asking for backtraces using the perf > infrastructure, etc.
I really like the idea. It's doable with minimal changes. The only question is the speed of uprobes. I just haven't benchmarked them. If uprobe+bpf is within 10% slower than this native refcnt debugger then I think we can build some really cool tools on top of it. Like generic debugging of std::shared_ptr or dead lock detection of unmodified binaries. We can uprobe into pthread_mutex_lock, etc. Infinite possibilites. -- To unsubscribe from this list: send the line "unsubscribe linux-perf-users" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
