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[ Upstream commit589f892ac8] The uart_ops startup() callback is called without interrupts disabled and without port->lock locked, relatively late during the boot process (from the call path of console_on_rootfs()). If the device is a console, it was already previously registered and could be actively printing messages. Since the startup() callback is reading/writing registers used by the console write() callback (AML_UART_CONTROL), its access must be synchronized using the port->lock. Currently it is not. The startup() callback is the only function that explicitly enables interrupts. Without the synchronization, it is possible that interrupts become accidentally permanently disabled. CPU0 CPU1 meson_serial_console_write meson_uart_startup -------------------------- ------------------ spin_lock(port->lock) val = readl(AML_UART_CONTROL) uart_console_write() writel(INT_EN, AML_UART_CONTROL) writel(val, AML_UART_CONTROL) spin_unlock(port->lock) Add port->lock synchronization to meson_uart_startup() to avoid racing with meson_serial_console_write(). Also add detailed comments to meson_uart_reset() explaining why it is *not* using port->lock synchronization. Link: https://lore.kernel.org/lkml/2a82eae7-a256-f70c-fd82-4e510750906e@samsung.com Fixes:ff7693d079("ARM: meson: serial: add MesonX SoC on-chip uart driver") Reported-by: Marek Szyprowski <m.szyprowski@samsung.com> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com> Reviewed-by: Petr Mladek <pmladek@suse.com> Reviewed-by: Jiri Slaby <jirislaby@kernel.org> Acked-by: Neil Armstrong <narmstrong@baylibre.com> Signed-off-by: John Ogness <john.ogness@linutronix.de> Link: https://lore.kernel.org/r/20220508103547.626355-1-john.ogness@linutronix.de Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
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.