[PATCH v3] DmaBufAllocator: Make DmaSyncer non-copyable
Cheng-Hao Yang
chenghaoyang at chromium.org
Mon Jan 13 17:43:27 CET 2025
Hi Barnabás,
On Mon, Jan 13, 2025 at 5:26 PM Barnabás Pőcze <pobrn at protonmail.com> wrote:
>
> Hi
>
>
> 2025. január 13., hétfő 17:16 keltezéssel, Milan Zamazal <mzamazal at redhat.com> írta:
>
> > Hi Harvey,
> >
> > Cheng-Hao Yang <chenghaoyang at chromium.org> writes:
> >
> > > Hi Milan,
> > >
> > > On Mon, Jan 13, 2025 at 3:44 PM Milan Zamazal <mzamazal at redhat.com> wrote:
> > >>
> > >> Hi,
> > >>
> > >> Harvey Yang <chenghaoyang at chromium.org> writes:
> > >>
> > >> > As DmaSyncer does sync start/end in the c'tor/d'tor, copying a DmaSyncer
> > >> > instance would trigger sync end earlier than expected. This patch makes
> > >> > it non-copyable to avoid the issue.
> > >>
> > >> After this patch, software ISP still works but reports the following
> > >> error on each frame:
> > >
> > > May I know what the environment is? (Unit tests or specific tests
> > > you're running?
> >
> > No tests, running `cam' with software ISP.
> >
> > >> ERROR DmaBufAllocator dma_buf_allocator.cpp:344 Unable to sync dma fd: -1, err: Bad file descriptor,
> > >> flags: 5
> > >
> > > Based on the log, `fd_.get()` is -1. Could you confirm that
> > > `plane.fd.get()` below is never `-1`?
> >
> > Yes, they are never -1.
> >
> > The problem occurs in the following line from the snippet below:
> >
> > dmaSyncers.emplace_back(plane.fd, DmaSyncer::SyncType::Write);
> >
> > It processes the input plane fine and calls DmaSyncer::sync with the
> > right fd, then it process the output plane and it first calls
> > DmaSyncer::sync with the right fd, followed by a call with fd -1.
> > Here is the backtrace of the corresponding call (note the
> > line numbers are a bit off due to debugging prints I inserted):
> >
> > #0 0x0000fffff7f0810c in libcamera::DmaSyncer::sync (this=this at entry=0xffffe4000bf0, step=step at entry=4) at ../src/libcamera/dma_buf_allocator.cpp:341
> > #1 0x0000fffff7f08228 in libcamera::DmaSyncer::~DmaSyncer (this=this at entry=0xffffe4000bf0, __in_chrg=<optimized out>) at ../src/libcamera/dma_buf_allocator.cpp:329
> > #2 0x0000fffff7f68fe4 in std::_Destroy<libcamera::DmaSyncer> (__pointer=0xffffe4000bf0) at /usr/include/c++/11/bits/stl_construct.h:151
> > #3 std::_Destroy_aux<false>::__destroy<libcamera::DmaSyncer*> (__last=<optimized out>, __first=0xffffe4000bf0) at /usr/include/c++/11/bits/stl_construct.h:163
> > #4 std::_Destroy<libcamera::DmaSyncer*> (__last=<optimized out>, __first=<optimized out>) at /usr/include/c++/11/bits/stl_construct.h:196
> > #5 std::_Destroy<libcamera::DmaSyncer*, libcamera::DmaSyncer> (__last=0xffffe4000c08, __first=0xffffe4000bf0) at /usr/include/c++/11/bits/alloc_traits.h:848
> > #6 std::vector<libcamera::DmaSyncer, std::allocator<libcamera::DmaSyncer> >::_M_realloc_insert<libcamera::SharedFD const&, libcamera::DmaSyncer::SyncType> (this=0xffffefe0d738, __position=...,
> > __position at entry=...) at /usr/include/c++/11/bits/vector.tcc:498
> > #7 0x0000fffff7f691b4 in std::vector<libcamera::DmaSyncer, std::allocator<libcamera::DmaSyncer> >::emplace_back<libcamera::SharedFD const&, libcamera::DmaSyncer::SyncType> (this=this at entry=0xffffefe0d738)
> > at /usr/include/c++/11/bits/vector.tcc:121
> > #8 0x0000fffff7f66d38 in libcamera::DebayerCpu::process (this=0xfffff001e8d0, frame=0, input=0xfffff0020270, output=0xfffff0018f70, params=...) at ../src/libcamera/software_isp/debayer_cpu.cpp:752
> >
> > This means DmaSyncer::sync is called twice within emplace_back, the
> > second time from the destructor with the invalid fd. This is weird,
> > what's the destroyed instance and why does it happen only with the
> > output plane and not the input plane? dmaSyncers is a local variable
> > not used anywhere else, I suspect the vector gets resized and some
> > unwanted actions on the instances happen during the operation.
>
> When the vector is resized, it must destroy the objects in the old storage.
> See the call to `_M_realloc_insert()` in the stack trace. Hence the call to the
> destructor during `emplace_back()`.
>
> And the reason why this did not happen previously is that previously the vector
> selected the copy constructor for moving the objects between allocation because
> the move constructor is not `noexcept` (because `SharedFD`'s corresponding methods
> are not `noexcept` - this should probably be fixed in any case).
>
> But since this change it must choose the move constructor because the copy
> constructor is deleted. And the move constructor leaves `SharedFd::fd_ == nullptr`,
> so `SharedFD::get()` returns -1.
>
> This also means that previously the syncs were probably off due to the destructor calls.
Thanks! That perfectly explains the error log.
In `DmaSyncer::sync`, it should confirm `fd_.isValid() == true` before
executing the sync.
Milan, could you try
https://gitlab.freedesktop.org/chenghaoyang/libcamera/-/commit/7a376b4b2f1fa0dd06a9cea268df5dbb12d357e9?
I'll upload another patch after the pipeline tests are passed.
Thanks,
Harvey
>
>
> Regards,
> Barnabás Pőcze
>
>
> >
> > > BR,
> > > Harvey
> > >
> > >>
> > >> DmaSyncer is used only in debayer_cpu.cpp:
> > >>
> > >> std::vector<DmaSyncer> dmaSyncers;
> > >> for (const FrameBuffer::Plane &plane : input->planes())
> > >> dmaSyncers.emplace_back(plane.fd, DmaSyncer::SyncType::Read);
> > >>
> > >> for (const FrameBuffer::Plane &plane : output->planes())
> > >> dmaSyncers.emplace_back(plane.fd, DmaSyncer::SyncType::Write);
> > >>
> > >> green_ = params.green;
> > >> red_ = swapRedBlueGains_ ? params.blue : params.red;
> > >> blue_ = swapRedBlueGains_ ? params.red : params.blue;
> > >>
> > >> /* Copy metadata from the input buffer */
> > >> FrameMetadata &metadata = output->_d()->metadata();
> > >> metadata.status = input->metadata().status;
> > >> metadata.sequence = input->metadata().sequence;
> > >> metadata.timestamp = input->metadata().timestamp;
> > >>
> > >> MappedFrameBuffer in(input, MappedFrameBuffer::MapFlag::Read);
> > >> MappedFrameBuffer out(output, MappedFrameBuffer::MapFlag::Write);
> > >> if (!in.isValid() || !out.isValid()) {
> > >> LOG(Debayer, Error) << "mmap-ing buffer(s) failed";
> > >> metadata.status = FrameMetadata::FrameError;
> > >> return;
> > >> }
> > >>
> > >> stats_->startFrame();
> > >>
> > >> if (inputConfig_.patternSize.height == 2)
> > >> process2(in.planes()[0].data(), out.planes()[0].data());
> > >> else
> > >> process4(in.planes()[0].data(), out.planes()[0].data());
> > >>
> > >> metadata.planes()[0].bytesused = out.planes()[0].size();
> > >>
> > >> dmaSyncers.clear();
> > >>
> > >> Any idea what could be wrong?
> > >>
> > >> > Fixes: 39482d59fe71 ("DmaBufAllocator: Add Dma Buffer synchronization function & helper class")
> > >> > Signed-off-by: Harvey Yang <chenghaoyang at chromium.org>
> > >> > Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> > >> > Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > >> > ---
> > >> > include/libcamera/internal/dma_buf_allocator.h | 5 +++++
> > >> > src/libcamera/dma_buf_allocator.cpp | 12 ++++++++++++
> > >> > 2 files changed, 17 insertions(+)
> > >> >
> > >> > diff --git a/include/libcamera/internal/dma_buf_allocator.h b/include/libcamera/internal/dma_buf_allocator.h
> > >> > index fc5de2c13edd..d26f8a74f4c6 100644
> > >> > --- a/include/libcamera/internal/dma_buf_allocator.h
> > >> > +++ b/include/libcamera/internal/dma_buf_allocator.h
> > >> > @@ -60,9 +60,14 @@ public:
> > >> >
> > >> > explicit DmaSyncer(SharedFD fd, SyncType type = SyncType::ReadWrite);
> > >> >
> > >> > + DmaSyncer(DmaSyncer &&other) = default;
> > >> > + DmaSyncer &operator=(DmaSyncer &&other) = default;
> > >> > +
> > >> > ~DmaSyncer();
> > >> >
> > >> > private:
> > >> > + LIBCAMERA_DISABLE_COPY(DmaSyncer)
> > >> > +
> > >> > void sync(uint64_t step);
> > >> >
> > >> > SharedFD fd_;
> > >> > diff --git a/src/libcamera/dma_buf_allocator.cpp b/src/libcamera/dma_buf_allocator.cpp
> > >> > index 3cc52f9686b0..a014c3b4263c 100644
> > >> > --- a/src/libcamera/dma_buf_allocator.cpp
> > >> > +++ b/src/libcamera/dma_buf_allocator.cpp
> > >> > @@ -311,6 +311,18 @@ DmaSyncer::DmaSyncer(SharedFD fd, SyncType type)
> > >> > sync(DMA_BUF_SYNC_START);
> > >> > }
> > >> >
> > >> > +/**
> > >> > + * \fn DmaSyncer::DmaSyncer(DmaSyncer &&other);
> > >> > + * \param[in] other The other instance
> > >> > + * \brief Enable move on class DmaSyncer
> > >> > + */
> > >> > +
> > >> > +/**
> > >> > + * \fn DmaSyncer::operator=(DmaSyncer &&other);
> > >> > + * \param[in] other The other instance
> > >> > + * \brief Enable move on class DmaSyncer
> > >> > + */
> > >> > +
> > >> > DmaSyncer::~DmaSyncer()
> > >> > {
> > >> > sync(DMA_BUF_SYNC_END);
> > >>
> >
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