Re: [BUG] segfault in perf-top -- thread refcnt

From: Jiri Olsa <jolsa@redhat.com>
To: David Ahern <dsahern@gmail.com>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
	Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
	Stephane Eranian <eranian@google.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [BUG] segfault in perf-top -- thread refcnt
Date: Mon, 30 Mar 2015 13:21:08 +0200	[thread overview]
Message-ID: <20150330112108.GG1413@krava> (raw)
In-Reply-To: <20150330102220.GE1413@krava>

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:
> 
> SNIP
> 
> > > 
> > > 2 things:
> > > 1. let run for a long time. go about using the server. do lots of builds,
> > > etc. it takes time
> > > 
> > > 2. use a box with a LOT of cpus (1024 in my case)
> > > 
> > > Make sure ulimit is set to get the core.
> > 
> > reproduced under 24 cpu box with kernel build (make -j25)
> > running on background.. will try to look closer
> > 
> > perf: Segmentation fault
> > -------- backtrace --------
> > ./perf[0x4fd79b]
> > /lib64/libc.so.6(+0x358f0)[0x7f9cbff528f0]
> > ./perf(thread__put+0x5b)[0x4b1a7b]
> > ./perf(hists__delete_entries+0x70)[0x4c8670]
> > ./perf[0x436a88]
> > ./perf[0x4fa73d]
> > ./perf(perf_evlist__tui_browse_hists+0x97)[0x4fc437]
> > ./perf[0x4381d0]
> > /lib64/libpthread.so.0(+0x7ee5)[0x7f9cc1ff2ee5]
> > /lib64/libc.so.6(clone+0x6d)[0x7f9cc0011b8d]
> > [0x0]
> 
> looks like race among __machine__findnew_thread and thread__put
> over the machine->threads rb_tree insert/removal
> 
> is there a reason why thread__put does not erase itself from machine->threads?
> 
> I'm trying attached patch.. so far so gut ;-)

arghh.. it blowed up during the lunch :-\

jirka