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Date:   Mon, 11 Nov 2019 17:07:38 +0100
From:   Jiri Olsa <jolsa@redhat.com>
To:     Alexey Budankov <alexey.budankov@linux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] perf session: Fix compression processing
Message-ID: <20191111160738.GD26980@krava>
References: <20191103222441.GE8251@krava>
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 <69782f54-f5f5-f89f-9c8d-172d4de331d0@linux.intel.com>
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 <84f6c330-95bc-b615-4366-8a243d1f5c20@linux.intel.com>
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On Mon, Nov 11, 2019 at 06:53:35PM +0300, Alexey Budankov wrote:
> On 11.11.2019 18:46, Jiri Olsa wrote:
> > On Mon, Nov 11, 2019 at 06:41:47PM +0300, Alexey Budankov wrote:
> >> On 11.11.2019 17:56, Jiri Olsa wrote:
> >>> On Mon, Nov 11, 2019 at 05:38:49PM +0300, Alexey Budankov wrote:
> >>>>
> >>>> On 04.11.2019 1:24, Jiri Olsa wrote:
> >>>>> hi,
> >>>> <SNIP>
> >>>>> ---
> >>>>> The compressed data processing occasionally fails with:
> >>>>>   $ perf report --stdio -vv
> >>>>>   decomp (B): 44519 to 163000
> >>>>>   decomp (B): 48119 to 174800
> >>>>>   decomp (B): 65527 to 131072
> >>>>>   fetch_mmaped_event: head=3D0x1ffe0 event->header_size=3D0x28, mma=
p_size=3D0x20000: fuzzed perf.data?
> >>>>>   Error:
> >>>>>   failed to process sample
> >>>>>   ...
> >>>>>
> >>>>> It's caused by recent fuzzer fix that does not take into account
> >>>>> that compressed data do not need to by fully present in the buffer,
> >>>>> so it's ok to just return NULL and not to fail.
> >>>>>
> >>>>> Fixes: 57fc032ad643 ("perf session: Avoid infinite loop when seeing=
 invalid header.size")
> >>>>> Link: http://lkml.kernel.org/n/tip-q1biqscs4stcmc9bs1iokfro@git.ker=
nel.org
> >>>>> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> >>>>> ---
> >>>>>  tools/perf/util/session.c | 8 +++++---
> >>>>>  1 file changed, 5 insertions(+), 3 deletions(-)
> >>>>>
> >>>>> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> >>>>> index f07b8ecb91bc..3589ed14a629 100644
> >>>>> --- a/tools/perf/util/session.c
> >>>>> +++ b/tools/perf/util/session.c
> >>>>> @@ -1959,7 +1959,7 @@ static int __perf_session__process_pipe_event=
s(struct perf_session *session)
> >>>>> =20
> >>>>>  static union perf_event *
> >>>>>  fetch_mmaped_event(struct perf_session *session,
> >>>>> -=09=09   u64 head, size_t mmap_size, char *buf)
> >>>>> +=09=09   u64 head, size_t mmap_size, char *buf, bool decomp)
> >>>>
> >>>> bools in interface make code less transparent.
> >>>>
> >>>>>  {
> >>>>>  =09union perf_event *event;
> >>>>> =20
> >>>>> @@ -1979,6 +1979,8 @@ fetch_mmaped_event(struct perf_session *sessi=
on,
> >>>>>  =09=09/* We're not fetching the event so swap back again */
> >>>>>  =09=09if (session->header.needs_swap)
> >>>>>  =09=09=09perf_event_header__bswap(&event->header);
> >>>>> +=09=09if (decomp)
> >>>>> +=09=09=09return NULL;
> >>>>>  =09=09pr_debug("%s: head=3D%#" PRIx64 " event->header_size=3D%#x, =
mmap_size=3D%#zx: fuzzed perf.data?\n",
> >>>>>  =09=09=09 __func__, head, event->header.size, mmap_size);
> >>>>>  =09=09return ERR_PTR(-EINVAL);
> >>>>> @@ -1997,7 +1999,7 @@ static int __perf_session__process_decomp_eve=
nts(struct perf_session *session)
> >>>>>  =09=09return 0;
> >>>>> =20
> >>>>>  =09while (decomp->head < decomp->size && !session_done()) {
> >>>>> -=09=09union perf_event *event =3D fetch_mmaped_event(session, deco=
mp->head, decomp->size, decomp->data);
> >>>>> +=09=09union perf_event *event =3D fetch_mmaped_event(session, deco=
mp->head, decomp->size, decomp->data, true);
> >>>>
> >>>> It looks like this call can be skipped, at all, in this case.
> >>>
> >>> not sure what you mean, we are in decomp code no?
> >>
> >> Ok, it is inside "not fetching" branch.=20
> >> NULL return value means to proceed getting further over the trace.
> >> Checking record type =3D=3D COMPRESSED at the higher level could=20
> >> probably be cleaner fix and also work faster.
> >=20
> > any chance you could post the fix? the patch I did was a
> > quick fix to get the feature working for presentation ;-)
> > you're probably thinking of the proper approach
>=20
> Please share the exact reproducing steps=20
> so I could come up with something.

'perf record -z' for longer workloads

jirka