From mboxrd@z Thu Jan 1 00:00:00 1970 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 D5F1B11181 for ; Tue, 16 Jan 2024 07:38:42 +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="fs+wz5Gv" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1705390721; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=EfBFl2eOx6dzP8++zlyYwBxQmYQ5RCeNDtKgTlcPQsc=; b=fs+wz5GvNF9czjwZpeMl56+kK4cMeSJ3iGoFCcd3FU/PjiPcIEVlCtSw2Yd+vEeKsvjXmD t5B+suYgu0n7GjhB6mvkEVl/j1wK6ePuscA0Ckw0ddMBb4lpeiLjf4TGwbUskteAmf2Zdn AFLGXhDs38BsNWFf4TTNi19l9AoR8Lc= Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-101-A5T5TWzFMJC88rNOftyKWA-1; Tue, 16 Jan 2024 02:38:40 -0500 X-MC-Unique: A5T5TWzFMJC88rNOftyKWA-1 Received: by mail-qk1-f199.google.com with SMTP id af79cd13be357-7816e45f957so1470650585a.1 for ; Mon, 15 Jan 2024 23:38:40 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1705390720; x=1705995520; h=content-transfer-encoding:content-disposition: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=EfBFl2eOx6dzP8++zlyYwBxQmYQ5RCeNDtKgTlcPQsc=; b=xVDHDSplX9HrLg/rrhCcDHgelieDZrY71IVDF8drMShGNlfZus80q/QBY09WkIGVYz we8cJDXkwvOIdAafHnnGNHNWxGJEE7IGJcdGhuzi16lgiOt6D8jg+V4Djn402D3ej+lL E6raxxPyIuhUxdSKB/+g9uDePJtt3/4TxLx+z4J7aoTqKhVK9JwIZsdMwwZaVH7vmy58 y0xXPeHqajGJs5UxdcRtRfGy1z1At5IkFfPlARH47y1AULZdBNMS7epDefKAKiIuRYcK 0Dx0zchDlAlk/dn6Qqo9uWw9qf4/to2m1RlVhVRRmhbLQag/RJQIuFzGalJcLoK1yLGU qJpw== X-Gm-Message-State: AOJu0YyyVtRMVMI7BnbEkQtgGskHH2rL+og3e0f7ISy30gUDRxDyl5Rq M3VuurjxOf37Zb9IrwMLj1JI0yJ0yqI3X7/9lmSs5fEy/nI+JzcdV2ee8ml4wMb5tXJh+s2Q6TT WZ9v8QqDSUdFdBECs+lE12tNLBAwM678E X-Received: by 2002:ae9:e70c:0:b0:77d:9d58:5467 with SMTP id m12-20020ae9e70c000000b0077d9d585467mr7714863qka.29.1705390720220; Mon, 15 Jan 2024 23:38:40 -0800 (PST) X-Google-Smtp-Source: AGHT+IFFWqf/DygCnGdiywzz4XsNxJmOIjslN7QxsPszTwWbtfzwY8dVLHuuYSFixUOAnf4MwkJmRg== X-Received: by 2002:ae9:e70c:0:b0:77d:9d58:5467 with SMTP id m12-20020ae9e70c000000b0077d9d585467mr7714855qka.29.1705390719971; Mon, 15 Jan 2024 23:38:39 -0800 (PST) Received: from LeoBras.redhat.com ([2804:1b3:a803:64aa:6db9:6544:60c:9e16]) by smtp.gmail.com with ESMTPSA id vr28-20020a05620a55bc00b0078199077d0asm3516021qkn.125.2024.01.15.23.38.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Jan 2024 23:38:39 -0800 (PST) From: Leonardo Bras To: Leonardo Bras Cc: Greg Kroah-Hartman , Jiri Slaby , Thomas Gleixner , Ilpo =?iso-8859-1?Q?J=E4rvinen?= , Andy Shevchenko , Florian Fainelli , John Ogness , Tony Lindgren , Marcelo Tosatti , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org Subject: Re: [RFC PATCH v1 0/2] Fix serial console for PREEMPT_RT Date: Tue, 16 Jan 2024 04:38:35 -0300 Message-ID: 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-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: 8bit On Tue, Jan 16, 2024 at 04:32:31AM -0300, Leonardo Bras wrote: > While dealing with a bug that breaks the serial console from qemu (8250) > after printing a lot of data, I found some issues on this driver on RT > as well as spurious IRQ behaviors that don't seem to be adeqate for RT. > > Comments: > Patch #1: > I found out this driver get an IRQ request for every tx byte, but the > handler is able to deal with sending multiple bytes per "thread wake up". > > Since the irqs_unhandled keep growing, and theads_handled don't change > as often, after some intense load (tx ~300kBytes) the serial will > disable the IRQ line for this driver, which ultimately breaks the console. > > My fist solution kept track of how many requests given handler dealt with, > which got added to theads_handled. On note_interrupt I got the diff from > theads_handled_last and subtracted that diff from irqs_unhandled. > > This solution required a change in the irqreturn_t typedef and a bunch of > helpers and defines, as well as adapting the 8250 driver. > At the end seemed like a overcomplicated solution for the issue, but it > can be an alternative if the current solution is considered imprecise. > > Mu cyrrent solution on patch #1 is much simpler, just keeping the > IRQ enabled as long as the irq_thread deal with any IRQ request before > irqs_unhandled hitting the limit value. > > Patch #2: > In RT, the 8250 driver has an issue if it's interrupted while holding the > port->lock. If the interruption needs to printk() anything, it > will try to get the port->lock, which is busy, so spin_lock() will try > to reschedule the interruption, which is in atomic context, and will > trigger a bug. > > This bug reproduces quite often, like in 50% of tests I did. > > The only thing I could think of for fixing this is using in_atomic() > when PREEMPT_RT=y, so it makes use of the same mechanism as for > oops_in_progress to avoid getting the lock if it's busy. It's working > just fine. > > Yeah, I got the warning in checkpath: > "ERROR: do not use in_atomic in drivers" > > So I need some feedback on what to do to avoid this bug, if not > by using in_atomic() at this driver. > > Since this one is linked to the console, any printk will try to get > this drivers port->lock, and so it's kind of hard to avoid this accesses. > > I though on doing an interface for spin_lock_only_if_can_sleep() but > it seemed overkill. > > Please provide comments / feedback. > > Thanks! > Leo > > > Leonardo Bras (2): > irq/spurious: Reset irqs_unhandled if an irq_thread handles one IRQ > request > serial/8250: Avoid getting lock in RT atomic context > > drivers/tty/serial/8250/8250_port.c | 2 +- > kernel/irq/spurious.c | 8 ++++++++ > 2 files changed, 9 insertions(+), 1 deletion(-) > > > base-commit: 052d534373b7ed33712a63d5e17b2b6cdbce84fd > -- > 2.43.0 > Resent this one with the correct order / patches.