On Tue, Mar 19, 2024 at 06:02:47PM +0000, Emil Kronborg wrote:
> The uart_handle_cts_change() function in serial_core expects the caller
> to hold uport->lock. For example, I have seen the below kernel splat,
> when the Bluetooth driver is loaded on an i.MX28 board.
>
> [ 85.119255] ------------[ cut here ]------------
> [ 85.124413] WARNING: CPU: 0 PID: 27 at /drivers/tty/serial/serial_core.c:3453 uart_handle_cts_change+0xb4/0xec
> [ 85.134694] Modules linked in: hci_uart bluetooth ecdh_generic ecc wlcore_sdio configfs
> [ 85.143314] CPU: 0 PID: 27 Comm: kworker/u3:0 Not tainted 6.6.3-00021-gd62a2f068f92 #1
> [ 85.151396] Hardware name: Freescale MXS (Device Tree)
> [ 85.156679] Workqueue: hci0 hci_power_on [bluetooth]
> (...)
> [ 85.191765] uart_handle_cts_change from mxs_auart_irq_handle+0x380/0x3f4
> [ 85.198787] mxs_auart_irq_handle from __handle_irq_event_percpu+0x88/0x210
> (...)
>
> Cc: stable@xxxxxxxxxxxxxxx # v6.1+
> Fixes: 4d90bb147ef6 ("serial: core: Document and assert lock requirements for irq helpers")
> Signed-off-by: Emil Kronborg <emil.kronborg@xxxxxxxxxxxxxx>
Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
> ---
> Changes in v2:
> - Add more of the stack trace to show why the lock is necessary. Note
> that i removed some unrelated noise for unwinding, showing and dumping
> the stack trace.
> - Add Fixes tag. Note that this commit do not fix 4d90bb147ef6 ("serial:
> core: Document and assert lock requirements for irq helpers") as such,
> but it was the closest commit I could find that makes sense.
> - Cc stable. Commit b0af4bcb4946 ("serial: core: Provide port lock
> wrappers") is a prerequisite. Therefore, v6.1+.
>
> drivers/tty/serial/mxs-auart.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c
> index 4749331fe618..1e8853eae504 100644
> --- a/drivers/tty/serial/mxs-auart.c
> +++ b/drivers/tty/serial/mxs-auart.c
> @@ -1086,11 +1086,13 @@ static void mxs_auart_set_ldisc(struct uart_port *port,
>
> static irqreturn_t mxs_auart_irq_handle(int irq, void *context)
> {
> - u32 istat;
> + u32 istat, stat;
> struct mxs_auart_port *s = context;
> u32 mctrl_temp = s->mctrl_prev;
> - u32 stat = mxs_read(s, REG_STAT);
>
> + uart_port_lock(&s->port);
> +
> + stat = mxs_read(s, REG_STAT);
> istat = mxs_read(s, REG_INTR);
>
> /* ack irq */
> @@ -1126,6 +1128,8 @@ static irqreturn_t mxs_auart_irq_handle(int irq, void *context)
> istat &= ~AUART_INTR_TXIS;
> }
>
> + uart_port_unlock(&s->port);
> +
> return IRQ_HANDLED;
> }
>
> --
> 2.44.0
>
>
