Re: perf top segfaults on current git

[Markus Trippelsdorf <markus@trippelsdorf.de>]

On 2015.11.04 at 13:27 +0100, Jiri Olsa wrote:
> On Wed, Nov 04, 2015 at 11:49:30AM +0100, Markus Trippelsdorf wrote:
> > On 2015.11.04 at 11:15 +0100, Markus Trippelsdorf wrote:
> > > On 2015.11.03 at 11:02 +0100, Ingo Molnar wrote:
> > > > 
> > > > Please pull the latest perf-core-for-linus git tree from:
> > > 
> > > Since the current merge "perf top" segfaults on my machine:
> > > 
> > > Program received signal SIGSEGV, Segmentation fault.
> > > 
> > > __map__is_kernel (map=map@entry=0x1abb7a0) at util/map.c:238
> > > 238             return __machine__kernel_map(map->groups->machine, map->type) == map;
> > > (gdb) bt
> > > #0  __map__is_kernel (map=map@entry=0x1abb7a0) at util/map.c:238
> > > #1  0x00000000004393e4 in symbol_filter (map=map@entry=0x1abb7a0, sym=sym@entry=0x1a88560) at builtin-top.c:658
> > > #2  0x00000000004fcd4d in dso__load_sym (dso=dso@entry=0x166dae0, map=map@entry=0x1abb7a0, syms_ss=0x7fffffff7680, runtime_ss=runtime_ss@entry=0x7fffffff7680, 
> > >     filter=filter@entry=0x4393c0 <symbol_filter>, kmodule=0) at util/symbol-elf.c:1082
> > > #3  0x00000000004a64e0 in dso__load (dso=0x166dae0, map=map@entry=0x1abb7a0, filter=filter@entry=0x4393c0 <symbol_filter>) at util/symbol.c:1530
> > > #4  0x00000000004b941f in map__load (filter=0x4393c0 <symbol_filter>, map=<optimized out>) at util/map.c:289
> > > #5  map__find_symbol (map=0x1abb7a0, addr=40188, filter=0x4393c0 <symbol_filter>) at util/map.c:333
> > > #6  0x00000000004803b1 in perf_event__preprocess_sample (event=event@entry=0x7ffff6a7a5f0, machine=machine@entry=0x164c7b8, al=al@entry=0x7fffffff8a90, 
> > >     sample=sample@entry=0x7fffffff8b20) at util/event.c:1045
> > > #7  0x0000000000439837 in perf_event__process_sample (machine=0x164c7b8, sample=0x7fffffff8b20, evsel=0x164c320, event=0x7ffff6a7a5f0, tool=0x7fffffff8ef0)
> > >     at builtin-top.c:737
> > > #8  perf_top__mmap_read_idx (top=top@entry=0x7fffffff8ef0, idx=idx@entry=0) at builtin-top.c:870
> > > #9  0x000000000043b9ef in perf_top__mmap_read (top=0x7fffffff8ef0) at builtin-top.c:887
> > > #10 __cmd_top (top=0x7fffffff8ef0) at builtin-top.c:1000
> > > #11 cmd_top (argc=<optimized out>, argv=<optimized out>, prefix=<optimized out>) at builtin-top.c:1329
> > > #12 0x00000000004756b3 in run_builtin (p=p@entry=0x5b0608 <commands+264>, argc=argc@entry=2, argv=argv@entry=0x7fffffffe500) at perf.c:386
> > > #13 0x00000000004203e2 in handle_internal_command (argv=0x7fffffffe500, argc=2) at perf.c:447
> > > #14 run_argv (argv=0x7fffffffe290, argcp=0x7fffffffe29c) at perf.c:491
> > > #15 main (argc=2, argv=0x7fffffffe500) at perf.c:608
> > > 
> > > It only happens occasionally (~every third or fourth run).
> > 
> > Apparently it started with:
> > 
> > commit cfc5acd4c80b875d2f739d6a93562034aee5563f
> > Author: Arnaldo Carvalho de Melo <acme@redhat.com>
> > Date:   Wed Sep 23 15:15:54 2015 -0300
> > 
> >     perf top: Filter symbols based on __map__is_kernel(map)
> 
> I think it's correct to assume map->groups != NULL,
> IMO the change just uncovered another bug
> 
> I couldn't reproduce this, but I could find one place where this
> assumption is broken.. could you please try attached patch?

Your patch fixes the issue. 
Thanks.

-- 
Markus