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Date:   Mon, 11 Nov 2019 16:46:12 +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: <20191111154612.GC26980@krava>
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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, mmap_=
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 i=
nvalid header.size")
> >>> Link: http://lkml.kernel.org/n/tip-q1biqscs4stcmc9bs1iokfro@git.kerne=
l.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_events(=
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 *session=
,
> >>>  =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, mm=
ap_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_event=
s(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, decomp=
->head, decomp->size, decomp->data);
> >>> +=09=09union perf_event *event =3D fetch_mmaped_event(session, decomp=
->head, decomp->size, decomp->data, true);
> >>
> >> It looks like this call can be skipped, at all, in this case.
> >=20
> > not sure what you mean, we are in decomp code no?
>=20
> 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.

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

thanks,
jirka