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707947247e
In vb2_vmalloc_get_userptr() the framevector is created with the 'write' argument set to false when vb2_create_framevec() is called for OUTPUT buffers. So the pages are marked as read-only. However, userspace will write to these buffers since it will fill in the data to output. Since get_userptr is only called if the userptr of the queued buffer has changed since the last time that same buffer was queued, this will fail when the buffer contents is updated and the buffer is queued again. E.g., userspace fills buffer 1 with the output video and queues it. The first time get_userptr is called and the pages are grabbed and pinned in memory and marked read-only. The second time buffer 1 is filled with different video data and queued again. Since the userptr hasn't changed the get_userptr() callback isn't called again. Since the pages were marked as read-only the new contents isn't updated. Just always call vb2_create_framevec() with FOLL_WRITE to always allow writing to the buffers. Using USERPTR streaming with OUTPUT devices is almost never done. And when it is done it is via v4l2-compliance and a driver like vim2m. But since v4l2-compliance doesn't actually inspect the capture buffer and compare it to the original output buffer, this issue was never noticed. But the vicodec driver actually needs to parse the bitstream in the OUTPUT buffers and any errors there will be immediately noticed. So this time v4l2-compliance failed the USERPTR streaming test. Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.