From patchwork Thu Apr 4 23:24:00 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Finn Thain X-Patchwork-Id: 786126 Received: from fhigh2-smtp.messagingengine.com (fhigh2-smtp.messagingengine.com [103.168.172.153]) (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 6A16C13C66C; Thu, 4 Apr 2024 23:31:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=103.168.172.153 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712273473; cv=none; b=osKD9zxPCrOB2GTic23lu0ANqiY2DnQSoyFWQvjf9i7DmVS4jvg4E7UVxV5AwspM95+A4aSp8Xp3UMigTVSZlVfkpE6/rfmTLREICK3Lk2+7RdU7xdafRaQHebZhF5OLqlmZFLUA92AHTMjkOO8NVaVBhHJ/Ydh2pSohpuTr8gQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712273473; c=relaxed/simple; bh=gT3ISPrTb39TkoYxCl+zUy++inSKyXfqXfH+8D34BXY=; h=To:Cc:Message-Id:From:Subject:Date; b=cWAwo77prkjpdxL2/E02JC+ZOBvRwbqrrIBTsb/45Pl81XZx1v6THGLocX3Wo2MBQdEBq2XU+j7YaWn4a6mdninXvn4bJiwjDGpIQ1743LOvxIOYw5uH1DWnUxYB9AcT3yhfKbosnCO/DuW6YA+vWBivyQZfeNMY5v/YftNwb3g= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=linux-m68k.org; spf=none smtp.mailfrom=linux-m68k.org; dkim=pass (2048-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b=bVtCQEka; arc=none smtp.client-ip=103.168.172.153 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=linux-m68k.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux-m68k.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b="bVtCQEka" Received: from compute2.internal (compute2.nyi.internal [10.202.2.46]) by mailfhigh.nyi.internal (Postfix) with ESMTP id 7F3841140105; Thu, 4 Apr 2024 19:31:10 -0400 (EDT) Received: from mailfrontend1 ([10.202.2.162]) by compute2.internal (MEProxy); Thu, 04 Apr 2024 19:31:10 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-type:date:date:feedback-id :feedback-id:from:from:in-reply-to:message-id:reply-to:subject :subject:to:to:x-me-proxy:x-me-proxy:x-me-sender:x-me-sender :x-sasl-enc; s=fm2; t=1712273470; x=1712359870; bh=pK0jqIblLjOpZ HzUGqOIz32gEstS475diijrXkvB3eA=; b=bVtCQEkankDw3t6RGYiDd8/EY4b+5 OzQ9bQO+z+fvSgLNl4Hihj/3+1Iyt/j/7mRvoNEdx9nq0mzoPY82XWtyZ6CSelPJ hTMmdx59Zi1PlM439ffPVs8D6dHkR2+WxZxgJlt/NR3Ad1oBZUAh9wSbEnd6Abiw eZiiU7nZQmEespjylXWF4NzO3fpesz6tvLToDVZwG0/Kjyudz/odn0nT26lnK+m+ EzMUyA2YkcTH03g6pmPgKPNIwAh14/8ZpFNQvnv7YvVLYtcqXpGRYXUQsicsQQLL 60/U1Av/QVDDm7Xuzzq2wfz2uYrvA/Dsa++yY9htMb+aLQzBwGBfaUGlQ== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvledrudefledgvdegucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhepvfevkffhufffsedttdertddttddtnecuhfhrohhmpefhihhnnhcuvfhhrghi nhcuoehfthhhrghinheslhhinhhugidqmheikehkrdhorhhgqeenucggtffrrghtthgvrh hnpefftdekheelvddvtdetudelhfehhfejjeeuudeileettdeuleeigeefkeehvdevffen ucffohhmrghinhepghhithhhuhgsrdgtohhmpdhkvghrnhgvlhdrohhrghenucevlhhush htvghrufhiiigvpedtnecurfgrrhgrmhepmhgrihhlfhhrohhmpehfthhhrghinheslhhi nhhugidqmheikehkrdhorhhg X-ME-Proxy: Feedback-ID: i58a146ae:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 4 Apr 2024 19:31:07 -0400 (EDT) To: Greg Kroah-Hartman , Jiri Slaby Cc: Michael Ellerman , Nicholas Piggin , Christophe Leroy , "Aneesh Kumar K.V" , "Naveen N. Rao" , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-m68k@lists.linux-m68k.org, Benjamin Herrenschmidt , Andy Shevchenko Message-Id: <0df45bedded1249f6c6ec2c2fb0d9879da1841b7.1712273040.git.fthain@linux-m68k.org> From: Finn Thain Subject: [PATCH v2] serial/pmac_zilog: Remove flawed mitigation for rx irq flood Date: Fri, 05 Apr 2024 10:24:00 +1100 Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The mitigation was intended to stop the irq completely. That may be better than a hard lock-up but it turns out that you get a crash anyway if you're using pmac_zilog as a serial console: ttyPZ0: pmz: rx irq flood ! BUG: spinlock recursion on CPU#0, swapper/0 That's because the pr_err() call in pmz_receive_chars() results in pmz_console_write() attempting to lock a spinlock already locked in pmz_interrupt(). With CONFIG_DEBUG_SPINLOCK=y, this produces a fatal BUG splat. The spinlock in question is the one in struct uart_port. Even when it's not fatal, the serial port rx function ceases to work. Also, the iteration limit doesn't play nicely with QEMU, as can be seen in the bug report linked below. A web search for other reports of the error message "pmz: rx irq flood" didn't produce anything. So I don't think this code is needed any more. Remove it. Link: https://github.com/vivier/qemu-m68k/issues/44 Link: https://lore.kernel.org/all/1078874617.9746.36.camel@gaston/ Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Finn Thain Acked-by: Michael Ellerman (powerpc) --- Changed since v1: - Reworked commit log according to comments from Andy Shevchenko. --- drivers/tty/serial/pmac_zilog.c | 14 -------------- 1 file changed, 14 deletions(-) diff --git a/drivers/tty/serial/pmac_zilog.c b/drivers/tty/serial/pmac_zilog.c index c8bf08c19c64..77691fbbf779 100644 --- a/drivers/tty/serial/pmac_zilog.c +++ b/drivers/tty/serial/pmac_zilog.c @@ -210,7 +210,6 @@ static bool pmz_receive_chars(struct uart_pmac_port *uap) { struct tty_port *port; unsigned char ch, r1, drop, flag; - int loops = 0; /* Sanity check, make sure the old bug is no longer happening */ if (uap->port.state == NULL) { @@ -291,24 +290,11 @@ static bool pmz_receive_chars(struct uart_pmac_port *uap) if (r1 & Rx_OVR) tty_insert_flip_char(port, 0, TTY_OVERRUN); next_char: - /* We can get stuck in an infinite loop getting char 0 when the - * line is in a wrong HW state, we break that here. - * When that happens, I disable the receive side of the driver. - * Note that what I've been experiencing is a real irq loop where - * I'm getting flooded regardless of the actual port speed. - * Something strange is going on with the HW - */ - if ((++loops) > 1000) - goto flood; ch = read_zsreg(uap, R0); if (!(ch & Rx_CH_AV)) break; } - return true; - flood: - pmz_interrupt_control(uap, 0); - pmz_error("pmz: rx irq flood !\n"); return true; }