FAILED: patch "[PATCH] serial: mxs-auart: add spinlock around changing cts state" failed to apply to 5.15-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 54c4ec5f8c471b7c1137a1f769648549c423c026
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2024042353-mayday-porcupine-efb6@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

54c4ec5f8c47 ("serial: mxs-auart: add spinlock around changing cts state")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 54c4ec5f8c471b7c1137a1f769648549c423c026 Mon Sep 17 00:00:00 2001
From: Emil Kronborg <emil.kronborg@xxxxxxxxxxxxxx>
Date: Wed, 20 Mar 2024 12:15:36 +0000
Subject: [PATCH] serial: mxs-auart: add spinlock around changing cts state

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
Fixes: 4d90bb147ef6 ("serial: core: Document and assert lock requirements for irq helpers")
Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
Signed-off-by: Emil Kronborg <emil.kronborg@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240320121530.11348-1-emil.kronborg@xxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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;
 }