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From: Ian Jackson <Ian.Jackson@eu.citrix.com>
To: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Cc: Anders Kaseorg <andersk@MIT.EDU>,
	"xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
	Markus Armbruster <armbru@redhat.com>
Subject: Re: [PATCH] IRQ handling race and spurious IIR read in serial/8250.c
Date: Thu, 19 Feb 2009 17:52:59 +0000	[thread overview]
Message-ID: <18845.40059.190188.291643@mariner.uk.xensource.com> (raw)
In-Reply-To: <18834.63479.700909.321686@mariner.uk.xensource.com>

I wrote:
> In drivers/serial/8250.c in Linux there are two bugs:
>  1. UART_BUG_TXEN can be spuriously set, due to an IRQ race
>  2. The workaround then applied by the kernel is itself buggy

Markus Armbruster has also experienced this problem in a Xen
environment and has confirmed that my patch fixes it.

I think at the very least this change:

> Proposed initial band-aid fix (against 2.6.28.4):
> 
> Do not read IIR in serial8250_start_tx when UART_BUG_TXEN
> 
> Reading the IIR clears some oustanding interrupts so it is not safe.
> Instead, simply transmit immediately if the buffer is empty without
> regard to IIR.
> 
> Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>

should be made right away.

Ian.

  reply	other threads:[~2009-02-19 17:53 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1233800599.5398.0.camel@balanced-tree>
     [not found] ` <18827.7191.646173.99255@mariner.uk.xensource.com>
     [not found]   ` <1233862446.5676.28.camel@balanced-tree>
     [not found]     ` <1233870772.5676.40.camel@balanced-tree>
     [not found]       ` <18833.40557.119090.48930@mariner.uk.xensource.com>
     [not found]         ` <alpine.DEB.2.00.0902101249181.20723@vinegar-pot.mit.edu>
2009-02-11 16:08           ` Ian Jackson
2009-02-19 17:52             ` Ian Jackson [this message]
2009-02-19 18:37               ` [Xen-devel] " Markus Armbruster
2009-02-19 19:24             ` Jeremy Fitzhardinge
2009-03-12 17:57 Markus Armbruster
2009-03-12 18:09 ` Alan Cox
2009-03-12 19:30   ` Ian Jackson

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