6e0af29806
When reading buffer descriptors on RX or on TX completion, an
RX_USED/TX_USED bit is checked first to ensure that the descriptors have
been populated, i.e. the ownership has been transferred. However, there
are no memory barriers to ensure that the data protected by the
RX_USED/TX_USED bit is up-to-date with respect to that bit.
Specifically:
- TX timestamp descriptors may be loaded before ctrl is loaded for the
TX_USED check, which is racy as the descriptors may be updated between
the loads, causing old timestamp descriptor data to be used.
- RX ctrl may be loaded before addr is loaded for the RX_USED check,
which is racy as a new frame may be written between the loads, causing
old ctrl descriptor data to be used.
This issue exists for both macb_rx() and gem_rx() variants.
Fix the races by adding DMA read memory barriers on those paths and
reordering the reads in macb_rx().
I have not observed any actual problems in practice caused by these
being missing, though.
Tested on a ZynqMP based system.
Fixes: 89e5785fc8a6 ("[PATCH] Atmel MACB ethernet driver")
Signed-off-by: Anssi Hannula <anssi.hannula@bitwise.fi>
Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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.