[PATCH v2 3/3] test: gstreamer: Test memory lifetime
Laurent Pinchart
laurent.pinchart at ideasonboard.com
Mon May 13 15:32:18 CEST 2024
On Mon, May 13, 2024 at 01:35:04AM +0300, Laurent Pinchart wrote:
> On Thu, May 09, 2024 at 05:07:51PM +0100, Kieran Bingham wrote:
> > Quoting Nicolas Dufresne (2024-05-09 16:28:14)
> > > Le jeudi 09 mai 2024 à 15:57 +0100, Kieran Bingham a écrit :
> > > > Quoting Nicolas Dufresne (2024-03-05 15:30:58)
> > > > > From: Nicolas Dufresne <nicolas.dufresne at collabora.com>
> > > > >
> > > > > Test that everything works fine if a buffer outlives the pipeline.
> > > > >
> > > > > Signed-off-by: Nicolas Dufresne <nicolas.dufresne at collabora.com>
> > > > > ---
> > > > > .../gstreamer_memory_lifetime_test.cpp | 75 +++++++++++++++++++
> > > > > test/gstreamer/meson.build | 4 +-
> > > > > 2 files changed, 78 insertions(+), 1 deletion(-)
> > > > > create mode 100644 test/gstreamer/gstreamer_memory_lifetime_test.cpp
> > > > >
> > > > > diff --git a/test/gstreamer/gstreamer_memory_lifetime_test.cpp b/test/gstreamer/gstreamer_memory_lifetime_test.cpp
> > > > > new file mode 100644
> > > > > index 00000000..6d932e9e
> > > > > --- /dev/null
> > > > > +++ b/test/gstreamer/gstreamer_memory_lifetime_test.cpp
> > > > > @@ -0,0 +1,75 @@
> > > > > +/* SPDX-License-Identifier: GPL-2.0-or-later */
> > > > > +/*
> > > > > + * Copyright (C) 2024, Nicolas Dufresne
> > > > > + *
> > > > > + * gstreamer_memory_lifetime_test.cpp - GStreamer memory lifetime test
> > > > > + */
> > > > > +
> > > > > +#include <iostream>
> > > > > +#include <unistd.h>
> > > > > +
> > > > > +#include <gst/app/app.h>
> > > > > +#include <gst/gst.h>
> > > > > +
> > > > > +#include "gstreamer_test.h"
> > > > > +#include "test.h"
> > > > > +
> > > > > +using namespace std;
> > > > > +
> > > > > +class GstreamerMemoryLifetimeTest : public GstreamerTest, public Test
> > > > > +{
> > > > > +public:
> > > > > + GstreamerMemoryLifetimeTest()
> > > > > + : GstreamerTest()
> > > > > + {
> > > > > + }
> > > > > +
> > > > > +protected:
> > > > > + int init() override
> > > > > + {
> > > > > + if (status_ != TestPass)
> > > > > + return status_;
> > > > > +
> > > > > + appsink_ = gst_element_factory_make("appsink", nullptr);
> > > > > + if (!appsink_) {
> > > > > + g_printerr("Your installation is missing 'appsink'\n");
> > > > > + return TestFail;
> > > > > + }
> > > > > + g_object_ref_sink(appsink_);
> > > > > +
> > > > > + return createPipeline();
> > > > > + }
> > > > > +
> > > > > + int run() override
> > > > > + {
> > > > > + /* Build the pipeline */
> > > > > + gst_bin_add_many(GST_BIN(pipeline_), libcameraSrc_, appsink_, nullptr);
> > > > > + if (gst_element_link(libcameraSrc_, appsink_) != TRUE) {
> > > > > + g_printerr("Elements could not be linked.\n");
> > > > > + return TestFail;
> > > > > + }
> > > > > +
> > > > > + if (startPipeline() != TestPass)
> > > > > + return TestFail;
> > >
> > > Did not add a comment here, since "startPipeline()" should be obvious that we
> > > start the pipeline. It will raise the state to PLAYING state.
> >
> > Yes, startPipeline is obvious enough ;-)
> >
> > > > > +
> > > > > + sample_ = gst_app_sink_try_pull_sample(GST_APP_SINK(appsink_), GST_SECOND * 5);
> > >
> > > This is also a bit trivial, it pulls a sample from the pipeline.
> >
> > Agreed, but what's the impact in lifetime. do we expect a single buffer?
> > I think you're covering it on the comment below though.
> >
> > > > > + gst_element_set_state(pipeline_, GST_STATE_NULL);
> > >
> > > Here though, I should probably add a comment (well before the change to NULL
> > > state).
> > >
> > > /*
> > > * Stop the pipeline without releasing sample_. This ensures that we can hold
> > > * on memory while elements can release all their internal resources as required
> > > * by the NULL state definition.
> > > */
> >
> > Yes, that's what I think the test needs to document.
>
> +1. That's also the part I wasn't sure about.
>
> > > > > +
> > > > > + if (!sample_)
> > > > > + return TestFail;
> > > >
> > > > Is this the part that does the test? I don't really know how this test
> > > > is working.
> > >
> > > This is memory safety. As the doc says:
> > >
> > > https://gstreamer.freedesktop.org/documentation/applib/gstappsink.html?gi-language=c#gst_app_sink_pull_sample
> > >
> > > > Returns ( [transfer: full][nullable]) – a GstSample or NULL ...
> > >
> > > As it annoted nullable, not doing a null check if not safe. I'd, say, it would
> > > be annormal, so failing the test make sense, but its not really the expected
> > > failure spot for when the code was broken.
>
> Should/can it be checked before calling gst_element_set_state(), or is
> the order above important ? sample_ being a normal pointer I assume that
> the call to gst_element_set_state() won't modify it, but the order of
> the code made it feel like there was some magic happening.
>
> > Which is the point that spots the code is broken then? I seem to still
> > miss it ?
> >
> > > > Is it pulling a single buffer? Does set_state(GST_STATE_NULL) destroy
> > > > the pipeline?
> > >
> > > No, when moving to STATE_NULL, its is required
> > >
> > > > Any comments we can add here to make it clearer what is actually being
> > > > tested or happening? The code doesn't really tell me what's going on
> > > > under the hood.
> > >
> > > https://gstreamer.freedesktop.org/documentation/application-development/basics/elements.html?gi-language=c#element-states
> > >
> > > > GST_STATE_NULL: this is the default state. No resources are allocated in this
> > > state, so, transitioning to it will free all resources. The element must be in
> > > this state when its refcount reaches 0 and it is freed.
> > >
> > > Let me know if the suggested comment above would do for you.
> > >
> > > > Does the test for !sample_ really mean the buffer still exists and is
> > > > valid? Does the test need to do anything to /access/ the buffer to make
> > > > sure the test proves it succeeded?
> > > >
> > > > I expect it probably does as otherwise you'd have added more - but it's
> > > > just not obvious from the above.
> > >
> > > The bug being that libcamera crash when the memory is released, in this specific
> > > case it crash in cleanup(). But I suspect that we can drop the sample_ member,
> > > and simple manually unref the sample here (avoiding smart pointer, as it would
> > > be equally confusing).
> > >
> > > p.s. Btw, its hard for me to efficiently comment back on 2 months old patch, I
> > > don't remember much about it, I'm just reading the patch to reply here.
>
> Sorry for not replying earlier.
>
> > Sounds like a great reason to make sure we have comments in the code
> > that explain the 'why' :-)
> >
> > I'm fine with whatever comments you believe are appropriate. 'You' two
> > months later are probably the best reviewer here ;-)
>
> Another comment about this patch in particular. We tend to order this
> kind of series with the test coming first, and the fix coming next. This
> allows ensuring that the test fails, and that the fix fixes the issue.
> This guards against cases where the test would be incorrect and wouldn't
> showcase the actual problem, and the fix would also be bogus.
I confirm that this patch, without patch 1/3, causes a crash when
libcamera is compiled without ASan, and an ASan failure otherwise.
Tested-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > > > > +
> > > > > + return TestPass;
> > > > > + }
> > > > > +
> > > > > + void cleanup() override
> > > > > + {
> >
> > Are you saying the test is actually testing the issue /here/ ? If so -
> > can we add a comment explicitly saying that ?
> >
> > Otherwise this is just 'cleanup' code to me. That's why I was looking at
> > the null check of sample_ trying to figure out if that's how you were
> > determining if the test had failed (Becuase that's the only time you
> > return TestFail after the test actually starts).
> >
> >
> > I guess the failure point is that the test will crash, rather than
> > detect a failure. Would that also be noteworthy?
>
> That is worth a comment, yes.
>
> > > > > + g_clear_pointer(&sample_, gst_sample_unref);
> > > > > + g_clear_object(&appsink_);
> > > > > + }
> > > > > +
> > > > > +private:
> > > > > + GstElement *appsink_;
> > > > > + GstSample *sample_;
> > > > > +};
> > > > > +
> > > > > +TEST_REGISTER(GstreamerMemoryLifetimeTest)
> > > > > diff --git a/test/gstreamer/meson.build b/test/gstreamer/meson.build
> > > > > index f3ba5a23..70609b88 100644
> > > > > --- a/test/gstreamer/meson.build
> > > > > +++ b/test/gstreamer/meson.build
> > > > > @@ -8,12 +8,14 @@ gstreamer_tests = [
> > > > > {'name': 'single_stream_test', 'sources': ['gstreamer_single_stream_test.cpp']},
> > > > > {'name': 'multi_stream_test', 'sources': ['gstreamer_multi_stream_test.cpp']},
> > > > > {'name': 'device_provider_test', 'sources': ['gstreamer_device_provider_test.cpp']},
> > > > > + {'name': 'memory_lifetime_test', 'sources': ['gstreamer_memory_lifetime_test.cpp']},
> > > > > ]
> > > > > gstreamer_dep = dependency('gstreamer-1.0', required : true)
> > > > > +gstapp_dep = dependency('gstreamer-app-1.0', required : true)
> > > > >
> > > > > foreach test : gstreamer_tests
> > > > > exe = executable(test['name'], test['sources'], 'gstreamer_test.cpp',
> > > > > - dependencies : [libcamera_private, gstreamer_dep],
> > > > > + dependencies : [libcamera_private, gstreamer_dep, gstapp_dep],
> > > > > link_with : test_libraries,
> > > > > include_directories : test_includes_internal)
> > > > >
--
Regards,
Laurent Pinchart
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