Re: [PATCH v2 perf/core] perf script: fix a use after free crash.

[Arnaldo Carvalho de Melo]

Em Wed, Dec 28, 2016 at 05:39:47PM -0800, Krister Johansen escreveu:
> On Tue, Nov 22, 2016 at 04:01:06PM -0300, Arnaldo Carvalho de Melo wrote:
> >  #include "evlist.h"
> > @@ -979,6 +980,7 @@ iter_finish_cumulative_entry(struct hist_entry_iter *iter,
> >  {
> >  	zfree(&iter->priv);
> >  	iter->he = NULL;
> > +	map__zput(al->map);
 
> As part of trying to tie up the year-end loose-ends, I went back and
> re-tested a rebase'd version of this patch against perf/core.  I ended
> up with a merge that's identical to yours, except that I'm not seeing
> any assertion failures with 'perf top -g', 'perf script', or 'perf
> report'.  Was perf/core the branch that was giving you trouble?

Yeah, I just tested it with my tip/perf/core and got this:

     0.00%     0.00%  [kernel]                    [k] file_free_rcu
     0.00%     0.00%  [kernel]                    [k] timerqueue_del
     0.00%     0.00%  [kernel]                    [k] irq_work_run
     0.00%     0.00%  [kernel]                    [k] native_irq_return_iret
     0.00%     0.00%  [kernel]                    [k] native_sched_clock
perf: util/map.c:246: map__exit: Assertion
`!(!((&map->rb_node)->__rb_parent_color == (unsigned long)(&map->rb_node)))' failed.
                                                                                                                               Aborted
(core dumped)
[root@jouet 3.4]#

Tried it again with what is in Linus' tree + your patch and got the same
problem:

[acme@jouet linux]$ git remote -v | grep torvalds.*fetch
torvalds	git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git (fetch)
[acme@jouet linux]$ git checkout -b test-branch torvalds/master
Branch test-branch set up to track remote branch master from torvalds.
Switched to a new branch 'test-branch'
[acme@jouet linux]$ git cherry-pick f7347a33099dbad7e9fb3c22cea211f238bfd320
[test-branch 7d786f548b62] perf callchain: Fix a use after free crash due to refcounting bug
 Author: Krister Johansen <kjlx@xxxxxxxxxxxxxxxxxx>
 Date: Mon Jan 2 12:06:55 2017 -0300
 3 files changed, 19 insertions(+), 2 deletions(-)
[acme@jouet linux]$ rm -rf /tmp/build/perf/ ; mkdir -p /tmp/build/perf ; make O=/tmp/build/perf -C tools/perf install-bin
make: Entering directory '/home/acme/git/linux/tools/perf'
  BUILD:   Doing 'make -j4' parallel build
  HOSTCC   /tmp/build/perf/fixdep.o
<SNIP>

Then I run it with a higher frequency and no delay in refreshing the screen, to
stress the refcounting code:

# perf top -F 10000 -g -d 0

Do it while running something like 'make -j32 allmodconfig' to create lots of
short lived processes (or use stress-ng, etc).

+    0.79%     0.00%  [kernel]                    [k] search_binary_handler
+    0.79%     0.00%  [kernel]                    [k] do_execveat_common.isra.37
+    0.79%     0.00%  [kernel]                    [k] sys_execve
+    0.79%     0.00%  [kernel]                    [k] do_syscall_64
perf: util/map.c:246: map__exit: Assertion `!(!((&map->rb_node)->__rb_parent_color == (unsigned long)(&map->rb_node)))' failed.
                                                                                                                               Aborted (core dumped)
[root@jouet 3.4]# 

- Arnaldo