linux-kernel - [PATCH v1 01/12] serial: cpm_uart: Avoid suspicious locking

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Message-ID: <f7da5cdc9287960185829cfef681a7d8614efa1f.1691068700.git.christophe.leroy@csgroup.eu>
Date:   Thu,  3 Aug 2023 15:56:42 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Timur Tabi <timur@...nel.org>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-serial@...r.kernel.org
Subject: [PATCH v1 01/12] serial: cpm_uart: Avoid suspicious locking

  CHECK   drivers/tty/serial/cpm_uart/cpm_uart_core.c
drivers/tty/serial/cpm_uart/cpm_uart_core.c:1271:39: warning: context imbalance in 'cpm_uart_console_write' - unexpected unlock

Allthough 'nolock' is not expected to change, sparse find the following
form suspicious:

	if (unlikely(nolock)) {
		local_irq_save(flags);
	} else {
		spin_lock_irqsave(&pinfo->port.lock, flags);
	}

	cpm_uart_early_write(pinfo, s, count, true);

	if (unlikely(nolock)) {
		local_irq_restore(flags);
	} else {
		spin_unlock_irqrestore(&pinfo->port.lock, flags);
	}

Rewrite it a more obvious form:

	if (unlikely(oops_in_progress)) {
		local_irq_save(flags);
		cpm_uart_early_write(pinfo, s, count, true);
		local_irq_restore(flags);
	} else {
		spin_lock_irqsave(&pinfo->port.lock, flags);
		cpm_uart_early_write(pinfo, s, count, true);
		spin_unlock_irqrestore(&pinfo->port.lock, flags);
	}

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 drivers/tty/serial/cpm_uart/cpm_uart_core.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/drivers/tty/serial/cpm_uart/cpm_uart_core.c b/drivers/tty/serial/cpm_uart/cpm_uart_core.c
index 66afa9bea6bf..71366a4cea22 100644
--- a/drivers/tty/serial/cpm_uart/cpm_uart_core.c
+++ b/drivers/tty/serial/cpm_uart/cpm_uart_core.c
@@ -1255,19 +1255,14 @@ static void cpm_uart_console_write(struct console *co, const char *s,
 {
 	struct uart_cpm_port *pinfo = &cpm_uart_ports[co->index];
 	unsigned long flags;
-	int nolock = oops_in_progress;
 
-	if (unlikely(nolock)) {
+	if (unlikely(oops_in_progress)) {
 		local_irq_save(flags);
-	} else {
-		spin_lock_irqsave(&pinfo->port.lock, flags);
-	}
-
-	cpm_uart_early_write(pinfo, s, count, true);
-
-	if (unlikely(nolock)) {
+		cpm_uart_early_write(pinfo, s, count, true);
 		local_irq_restore(flags);
 	} else {
+		spin_lock_irqsave(&pinfo->port.lock, flags);
+		cpm_uart_early_write(pinfo, s, count, true);
 		spin_unlock_irqrestore(&pinfo->port.lock, flags);
 	}
 }
-- 
2.41.0