linux-kernel - [PATCH] serial: 8250: drop lockdep annotation from serial8250_clear

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Date:   Fri, 11 Aug 2023 08:43:40 +0200
From:   "Jiri Slaby (SUSE)" <jirislaby@...nel.org>
To:     gregkh@...uxfoundation.org
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Jiri Slaby (SUSE)" <jirislaby@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        John Ogness <john.ogness@...utronix.de>
Subject: [PATCH] serial: 8250: drop lockdep annotation from serial8250_clear_IER()

The port lock is not always held when calling serial8250_clear_IER().
When an oops is in progress, the lock is tried to be taken and when it
is not, a warning is issued:
 WARNING: CPU: 0 PID: 1 at drivers/tty/serial/8250/8250_port.c:707 	+0x57/0x60
 Modules linked in:
 CPU: 0 PID: 1 Comm: init Not tainted 6.5.0-rc5-1.g225bfb7-default+ #774 00f1be860db663ed29479b8255d3b01ab1135bd3
 Hardware name: QEMU Standard PC ...
 RIP: 0010:serial8250_clear_IER+0x57/0x60
...
 Call Trace:
  <TASK>
  serial8250_console_write+0x9e/0x4b0
  console_flush_all+0x217/0x5f0
...

Therefore, remove the annotation as it doesn't hold for all invocations.

The other option would be to make the lockdep test conditional on
'oops_in_progress' or pass 'locked' from serial8250_console_write(). I
don't think, that is worth it.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@...nel.org>
Reported-by: Vlastimil Babka <vbabka@...e.cz>
Cc: John Ogness <john.ogness@...utronix.de>
Fixes: d0b309a5d3f4 (serial: 8250: synchronize and annotate UART_IER access)
---
 drivers/tty/serial/8250/8250_port.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index ecfdc4534123..f59328e1c35d 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -703,9 +703,6 @@ static void serial8250_set_sleep(struct uart_8250_port *p, int sleep)

 static void serial8250_clear_IER(struct uart_8250_port *up)
 {
-	/* Port locked to synchronize UART_IER access against the console. */
-	lockdep_assert_held_once(&up->port.lock);
-
 	if (up->capabilities & UART_CAP_UUE)
 		serial_out(up, UART_IER, UART_IER_UUE);
 	else
-- 
2.41.0