Arnaldo, I just sent the patches I wrote to fix the bugs I ran into since yesterday.
On Fri, Jan 17, 2014 at 3:09 PM, Arnaldo Carvalho de Melo <[email protected]> wrote: > 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/
