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Mon, 15 Jan 2024 23:32:54 -0800 (PST) X-Received: by 2002:ac8:5bd2:0:b0:429:bdfc:3680 with SMTP id b18-20020ac85bd2000000b00429bdfc3680mr8717434qtb.97.1705390374251; Mon, 15 Jan 2024 23:32:54 -0800 (PST) Received: from LeoBras.redhat.com ([2804:1b3:a803:64aa:6db9:6544:60c:9e16]) by smtp.gmail.com with ESMTPSA id bs6-20020ac86f06000000b00429d6bd085csm3191262qtb.6.2024.01.15.23.32.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Jan 2024 23:32:53 -0800 (PST) From: Leonardo Bras To: Greg Kroah-Hartman , Jiri Slaby , Thomas Gleixner , =?utf-8?q?Ilpo_J=C3=A4rvinen?= , Andy Shevchenko , Florian Fainelli , John Ogness , Tony Lindgren , Marcelo Tosatti Cc: Leonardo Bras , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org Subject: [RFC PATCH v1 2/2] serial/8250: Avoid getting lock in RT atomic context Date: Tue, 16 Jan 2024 04:32:33 -0300 Message-ID: <20240116073234.2355850-4-leobras@redhat.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240116073234.2355850-2-leobras@redhat.com> References: <20240116073234.2355850-2-leobras@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1788231490979401006 X-GMAIL-MSGID: 1788231490979401006 With PREEMPT_RT enabled, a spin_lock_irqsave() becomes a possibly sleeping spin_lock(), without preempt_disable() or irq_disable(). This allows a task T1 to get preempted or interrupted while holding the port->lock. If the preempting task T2 need the lock, spin_lock() code will schedule T1 back until it finishes using the lock, and then go back to T2. There is an issue if a T1 holding port->lock is interrupted by an IRQ, and this IRQ handler needs to get port->lock for writting (printk): spin_lock() code will try to reschedule the interrupt handler, which is in atomic context, causing a BUG() for trying to reschedule/sleep in atomic context. So for the case (PREEMPT_RT && in_atomic()) try to get the lock, and if it fails proceed anyway, just like it's done in oops_in_progress case. Signed-off-by: Leonardo Bras --- drivers/tty/serial/8250/8250_port.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 8ca061d3bbb92..8480832846319 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -3397,7 +3397,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s, touch_nmi_watchdog(); - if (oops_in_progress) + if (oops_in_progress || (IS_ENABLED(CONFIG_PREEMPT_RT) && in_atomic()) locked = uart_port_trylock_irqsave(port, &flags); else uart_port_lock_irqsave(port, &flags);