Em Tue, Mar 02, 2021 at 01:47:55PM +0900, Namhyung Kim escreveu:
> Hello,
>
> On Tue, Mar 2, 2021 at 11:35 AM Dmitry Safonov <d...@arista.com> wrote:
> >
> > __cmd_diff() sets result of perf_session__new() to d->session.
> > In case of failure, it's errno and perf-diff may crash with:
> > failed to open perf.data: Permission denied
> > Failed to open perf.data
> > Segmentation fault (core dumped)
> >
> > From the coredump:
> > 0 0x00005569a62b5955 in auxtrace__free (session=0xffffffffffffffff)
> > at util/auxtrace.c:2681
> > 1 0x00005569a626b37d in perf_session__delete (session=0xffffffffffffffff)
> > at util/session.c:295
> > 2 perf_session__delete (session=0xffffffffffffffff) at util/session.c:291
> > 3 0x00005569a618008a in __cmd_diff () at builtin-diff.c:1239
> > 4 cmd_diff (argc=<optimized out>, argv=<optimized out>) at
> > builtin-diff.c:2011
> > [..]
> >
> > Funny enough, it won't always crash. For me it crashes only if failed
> > file is second in cmd-line: the reason is that cmd_diff() check files for
> > branch-stacks [in check_file_brstack()] and if the first file doesn't
> > have brstacks, it doesn't proceed to try open other files from cmd-line.
> >
> > Check d->session before calling perf_session__delete().
> >
> > Another solution would be assigning to temporary variable, checking it,
> > but I find it easier to follow with IS_ERR() check in the same function.
> > After some time it's still obvious why the check is needed, and with
> > temp variable it's possible to make the same mistake.
> >
> > Cc: Alexander Shishkin <alexander.shish...@linux.intel.com>
> > Cc: Arnaldo Carvalho de Melo <a...@kernel.org>
> > Cc: Ingo Molnar <mi...@redhat.com>
> > Cc: Jiri Olsa <jo...@redhat.com>
> > Cc: Mark Rutland <mark.rutl...@arm.com>
> > Cc: Namhyung Kim <namhy...@kernel.org>
> > Cc: Peter Zijlstra <pet...@infradead.org>
> > Signed-off-by: Dmitry Safonov <d...@arista.com>
>
> Acked-by: Namhyung Kim <namhy...@kernel.org>
Thanks, tested, added a complete set of steps for a problem to be
reproduced and applied.
- Arnaldo
Committer testing:
$ perf record sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.001 MB perf.data (8 samples) ]
$ perf diff
failed to open perf.data.old: No such file or directory
Failed to open perf.data.old
$ perf record sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.001 MB perf.data (8 samples) ]
$ perf diff
# Event 'cycles:u'
#
# Baseline Delta Abs Shared Object Symbol
# ........ ......... ................ ..........................
#
0.92% +87.66% [unknown] [k] 0xffffffff8825de16
11.39% +0.04% ld-2.32.so [.] __GI___tunables_init
87.70% ld-2.32.so [.] _dl_check_map_versions
$ sudo chown root:root perf.data
[sudo] password for acme:
$ perf diff
failed to open perf.data: Permission denied
Failed to open perf.data
Segmentation fault (core dumped)
$
After the patch:
$ perf diff
failed to open perf.data: Permission denied
Failed to open perf.data
$
Signed-off-by: Dmitry Safonov <d...@arista.com>
Acked-by: Namhyung Kim <namhy...@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <a...@redhat.com>
