From nobody Wed Dec 17 11:32:00 2025 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 283E611739 for ; Tue, 16 Jan 2024 07:33:03 +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="Of8PBbzi" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1705390382; 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=Of8PBbziYYO7EDZVezZwDQ4HKwdv4hIKdnEwiPPq+Foj1nP1ul6wExeqy4pUuH7E0qVKFC hEQi70CYlkLqwRu7XL9+c5lIJxvxg3QaMpu05ZerNzk0P7VAcGQNeygNkxdX+p8+5f2ZXD AHSCBKZ3YF0fRhFZkmH+zECpUWn3z3U= Received: from mail-qt1-f197.google.com (mail-qt1-f197.google.com [209.85.160.197]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-477-3ELGe3_HO--Cm7-MYZfULQ-1; Tue, 16 Jan 2024 02:32:54 -0500 X-MC-Unique: 3ELGe3_HO--Cm7-MYZfULQ-1 Received: by mail-qt1-f197.google.com with SMTP id d75a77b69052e-429f10775aeso17514991cf.0 for ; Mon, 15 Jan 2024 23:32:54 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1705390374; x=1705995174; 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=ptZsbhmf4RIEpoFpl4RFjq2+qCutKa5QZwyETuTw0eCEwOYRNIHwLnQtlK9OoyaQ26 xVOXHCAwk81N/UY5/F8JEz+hhs0hIP8wZjVXTB8pPHiaJQ2a9B/oJVILJyU0Y0UHjNgB zVtG5wBpmv7vYtRTQ0rQPy4pXkz46tO70D2fIx3pLqaN0SDpHz4LtCRxR4XzXNsOjLZn CUFaL3AyhCLTeuiGO+w5aY5SL+wc27h7FBcWAP2F3keywO8F5RYThyWerHkI5YZsQOM+ hQCimfRiP7uRzgWOec6eAAzsrD1fiLF2jjXQHLM+COWEN9zBpp3FlGNMuxyYX+OyqS9B 2kEQ== X-Gm-Message-State: AOJu0YzAU42KBZZ1zu5I3hTlGfADcZaKDPrCeNeW56GnavGJ0+XIbjXp sS8eAhxrgPYm9zMw3K+fSEzs4yID1U1xvEJuGLdUcCEpQhQSG0nD0yL1RkqIEGLGnnJolpsK4BA 5Vqr1Vjw17+g3vUboLd9B2kkEqxb0GBv1 X-Received: by 2002:ac8:5bd2:0:b0:429:bdfc:3680 with SMTP id b18-20020ac85bd2000000b00429bdfc3680mr8717441qtb.97.1705390374494; Mon, 15 Jan 2024 23:32:54 -0800 (PST) X-Google-Smtp-Source: AGHT+IGHJFpf/6ubQH2AthihuOoclhl9uHSJCCwkM4TRoRQC4bETdfKc++ioE0Ea8rqkV6W4u5nMvQ== 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=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: [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 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