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@vger.kernel.org # v6.1+ Fixes: 4d90bb147ef6 ("serial: core: Document and assert lock requirements for irq helpers") Signed-off-by: Emil Kronborg emil.kronborg@protonmail.com

Reviewed-by: Frank Li Frank.Li@nxp.com

---

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