Hi, In preparation for making the 8250 serial driver the first driver to support the upcoming atomic consoles [0], its console write() callback (serial8250_console_write) was evaluated. For this callback of the 8250 driver there are two critical writes to the UART_IER register: once to disable all interrupts before transmitting a line of text, and again after transmit to re-enable the previously enabled interrupts. These two writes are performed under a single synchronized section protected by the port lock. I then checked all other access to UART_IER in the 8250 driver to see if they always occurred under the port lock. If not, it would be possible that the console write() callback could overwrite or restore incorrect values to UART_IER. This is illustrated in the commit message of the first patch. Indeed several call sites were discovered where UART_IER is accessed without the port lock. This series adds the missing locking in order to ensure UART_IER access is always synchronized against the console write() callback. For call sites where UART_IER access was already performed under the port lock, this series adds code comments and (when appropriate) lockdep notation to help catch any future issues that may creep in. Note that some of the new usage of port lock is not strictly necessary, because (for example) the console is disabled before it is suspended. However, these are not hot paths and by taking the port lock it simplifies the synchronization semantics for UART_IER to allow general lockdep usage. Also note that none of these patches have been tagged for stable. The possible stable candidates do include Fixes tags. But since the fixes are not based on real-world reports, it probably is not necessary to backport them. John Ogness [0] https://lore.kernel.org/lkml/20230302195618.156940-1-john.ogness@xxxxxxxxxxxxx John Ogness (8): serial: 8250: lock port in startup() callbacks serial: core: lock port for stop_rx() in uart_suspend_port() serial: 8250: lock port for stop_rx() in omap8250_irq() serial: core: lock port for start_rx() in uart_resume_port() serial: 8250: lock port for rx_dma() callback serial: 8250: lock port for omap8250_restore_regs() serial: 8250: lock port for UART_IER access in omap8250_irq() serial: 8250: synchronize and annotate UART_IER access drivers/tty/serial/8250/8250.h | 6 ++ drivers/tty/serial/8250/8250_aspeed_vuart.c | 3 + drivers/tty/serial/8250/8250_bcm7271.c | 4 ++ drivers/tty/serial/8250/8250_exar.c | 4 ++ drivers/tty/serial/8250/8250_mtk.c | 9 +++ drivers/tty/serial/8250/8250_omap.c | 41 +++++++++++- drivers/tty/serial/8250/8250_port.c | 71 ++++++++++++++++++++- drivers/tty/serial/serial_core.c | 10 ++- 8 files changed, 141 insertions(+), 7 deletions(-) base-commit: d5b3d02d0b107345f2a6ecb5b06f98356f5c97ab -- 2.30.2
