From nobody Wed Dec 17 11:30:42 2025 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 220E1111BA for ; Tue, 16 Jan 2024 07:37:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="OB49gEbT" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1705390635; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Ev/EHro7bSIb21ohSGiRASekMY9/Fc0MaRbZNwxLwJc=; b=OB49gEbTkLQEFPrYhHvND7pp2kEZR9JwlKaDSudTMKRW2pFkNrTfrrbLSACGNrWM4UFt1P PQvW0WATT0Q9a3NwVKIBH7NSJK+amfXP+qkiJZbl3Gik04NsDY3TM9mKlXyr6USHoaMUiJ pbZAY5KwsXHT1aG9Y3qTGbU/+IaWZPQ= Received: from mail-qv1-f70.google.com (mail-qv1-f70.google.com [209.85.219.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-86-ldK5bRqMOJOfZEXcqyINLA-1; Tue, 16 Jan 2024 02:37:13 -0500 X-MC-Unique: ldK5bRqMOJOfZEXcqyINLA-1 Received: by mail-qv1-f70.google.com with SMTP id 6a1803df08f44-681684ca881so10823276d6.2 for ; Mon, 15 Jan 2024 23:37:13 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1705390632; x=1705995432; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=Ev/EHro7bSIb21ohSGiRASekMY9/Fc0MaRbZNwxLwJc=; b=MqnEW4YeOk2AZ+a/zKfrPrLO+6rA29GGg4Ae72ksm2Gltn4q6kUOhz5O9WeTncawKr jdi8rmYDrmlz5GMNiqJo0cpgpSZegIfAbOPo4vG3lLXah4kO6JAjUmEG/wFSwEvSTOVu EW64ClFNBZFT3c0nCHUG2lStsTL4idcqlNZAr92DvSCAnHI2ltbh7MHHW+kBMFi17Sy3 ct05kWCZ1pKa4eCmVAyyNrZAx2Vdx5LQ9OV2Xxn0Xdux4WtcHJ3Yncjp4EYCMOQgzgtA 4vA9+TNIG7NSyFr4jKj0LFUcH4a+xlbkxRNrSlEXMU3OMb4vH+Zar10R0AYdNOb7pzO5 yO4g== X-Gm-Message-State: AOJu0YzQPufBQYigIYaZJ7Lk4/lU12r78NDhqbIy8BwjxPUyFi9kueSr 07oOL39PlWf1cz0JokFhRN7neZ/J7PZJOrwFXATfF1OF74fi2KiNK4xJH1db6A+YssXOwn2IX49 wOmHZx/dv7MuezVPXCp92zauUSlt4vHeH X-Received: by 2002:ad4:5b8f:0:b0:681:5c24:723 with SMTP id 15-20020ad45b8f000000b006815c240723mr4640540qvp.46.1705390632761; Mon, 15 Jan 2024 23:37:12 -0800 (PST) X-Google-Smtp-Source: AGHT+IGrNcqol/OiEQ5ZrUIjTn7g2kuQvDjo2VGcjjAoLMRJtf3rUoTzhAFjIwMmgvbUMKAlwvpo2Q== X-Received: by 2002:ad4:5b8f:0:b0:681:5c24:723 with SMTP id 15-20020ad45b8f000000b006815c240723mr4640532qvp.46.1705390632538; Mon, 15 Jan 2024 23:37:12 -0800 (PST) Received: from LeoBras.redhat.com ([2804:1b3:a803:64aa:6db9:6544:60c:9e16]) by smtp.gmail.com with ESMTPSA id jc4-20020a05622a714400b00429acfe5bb4sm4650206qtb.40.2024.01.15.23.37.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Jan 2024 23:37:12 -0800 (PST) From: Leonardo Bras To: Greg Kroah-Hartman , Jiri Slaby , Thomas Gleixner , =?UTF-8?q?Ilpo=20J=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: [RESEND RFC PATCH v1 2/2] serial/8250: Avoid getting lock in RT atomic context Date: Tue, 16 Jan 2024 04:37:00 -0300 Message-ID: <20240116073701.2356171-3-leobras@redhat.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240116073701.2356171-1-leobras@redhat.com> References: <20240116073701.2356171-1-leobras@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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, =20 touch_nmi_watchdog(); =20 - if (oops_in_progress) + if (oops_in_progress || (IS_ENABLED(CONFIG_PREEMPT_RT) && in_atomic()) locked =3D uart_port_trylock_irqsave(port, &flags); else uart_port_lock_irqsave(port, &flags); --=20 2.43.0