Messages in this thread | | | Date | Mon, 30 Mar 2015 10:59:58 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [BUG] segfault in perf-top -- thread refcnt |
| |
Em Mon, Mar 30, 2015 at 03:20:59PM +0200, Jiri Olsa escreveu: > On Mon, Mar 30, 2015 at 10:07:08AM -0300, Arnaldo Carvalho de Melo wrote: > > Em Mon, Mar 30, 2015 at 02:56:31PM +0200, Jiri Olsa escreveu: > > > On Mon, Mar 30, 2015 at 09:48:52PM +0900, Namhyung Kim wrote: > > > > Hi Jiri, > > > > > > > > On Mon, Mar 30, 2015 at 01:49:07PM +0200, Jiri Olsa wrote: > > > > > On Mon, Mar 30, 2015 at 01:21:08PM +0200, Jiri Olsa wrote: > > > > > > On Mon, Mar 30, 2015 at 12:22:20PM +0200, Jiri Olsa wrote: > > > > > > > On Mon, Mar 30, 2015 at 10:07:37AM +0200, Jiri Olsa wrote: > > > > > - th = thread__new(pid, tid); > > > > > + th = thread__new(machine, pid, tid); > > > > > if (th != NULL) { > > > > > + > > > > > + pthread_mutex_lock(&machine->threads_lock); > > > > > rb_link_node(&th->rb_node, parent, p); > > > > > rb_insert_color(&th->rb_node, &machine->threads); > > > > > + pthread_mutex_unlock(&machine->threads_lock); > > > > > > > > I think you also need to protect the rb tree traversal above. > > > > > > yep, I already have another version.. but it blows on another place ;-) > > > > Well, why? The point of refcounting is that the structure will not go > > away while we have it in the rbtree. > > > > Or are you talking about two threads trying to insert entries in the > > rbtree? Can you point where this can happen? > > yep, as I wrote in previous email: > > > looks like race among __machine__findnew_thread and thread__put > > over the machine->threads rb_tree insert/removal > > update thread: > perf_event__process_sample > perf_event__preprocess_sample > machine__findnew_thread > traverse machine->threads > > display thread: > perf_top__sort_new_samples > hists__delete_entries > ... > hist_entry__delete(struct hist_entry *he) > thread__zput(he->thread); > > > > > > > But this makes every sample processing grabs and releases the lock so > > > > might cause high overhead. It can be a problem if such processing is > > > > done parallelly like my multi-thread work. :-/ > > > > > yep.. perhaps instead of more locking we need to find a way where > > > only single thread do the update on hists/threads > > > > But that should be really rare, no? The problem is to search in one > > thread (the fast path) and inserting entries (slow path), no? > > there're many new threads on kernel make -j25 workload ;-)
yeah, dumb me, hey, its still early here in .br ;-)
- Arnaldo
| |