Em Fri, Jan 17, 2014 at 10:00:20AM +0100, Stephane Eranian escreveu: > The issue boils down to the fact that evsels have their file descriptors > closed > twice nowadays. Once in __run_per_stat() via perf_evsel__close_fd() and > twice in perf_evlist__close(). > Now, calling close() twice is okay. However the fd is then set to -1. > That's still okay with close(). The problem is elsewhere. > It comes from the ncpus argument passed to perf_evsel__close(). It is > DIFFERENT between the evsel and the evlist when cpumask are used. > Take my case, 8 CPUs machine but a 1 CPU cpumask. The evsel allocates > the xyarray for 1 CPU 1 thread. The fd are first close with 1 CPU, 1 thread. > But then evlist_close() comes in and STILL thinks the events were using > 8 CPUs, 1 thread and thus a xyarray of that size. And this causes writes > to entries that are beyond the xyarray when the fds are set to -1, thereby > causing memory corruption which I was lucky to catch via glibc. > First, why are we closing the descriptors twice?
The idea here was to reduce the boilerplate that tools need to do when they are done dealing with evlists, so evlist__delete would do what the kernel does to resources allocated to a thread when it exits without explicitely deallocating them: release them all. So it seems, from your analysis, that bugs were left that need to be hammered out so that this works as intended. Can you share your patch? > Second, I have a fix that seems to work for me. It uses the evsel->cpus > if evsel->cpus exists, otherwise it defaults to evtlist->cpus. Looks like > a reasonable thing to do to me, but is it? I would rather avoid the double > close altogether. > > > Opinion? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
