From: Markus Armbruster <armbru@redhat.com>
To: Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"xen-devel\@lists.xensource.com" <xen-devel@lists.xensource.com>,
Anders Kaseorg <andersk@MIT.EDU>
Subject: Re: [Xen-devel] Re: [PATCH] IRQ handling race and spurious IIR read in serial/8250.c
Date: Thu, 19 Feb 2009 19:37:53 +0100 [thread overview]
Message-ID: <87vdr6z30e.fsf@pike.pond.sub.org> (raw)
In-Reply-To: <18845.40059.190188.291643@mariner.uk.xensource.com> (Ian Jackson's message of "Thu\, 19 Feb 2009 17\:52\:59 +0000")
Ian Jackson <Ian.Jackson@eu.citrix.com> writes:
> 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.
Correct.
> 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.
Patch makes sense to me.
Acked-by: Markus Armbruster <armbru@redhat.com>
WARNING: multiple messages have this Message-ID (diff)
From: Markus Armbruster <armbru@redhat.com>
To: Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Anders Kaseorg <andersk@MIT.EDU>
Subject: Re: Re: [PATCH] IRQ handling race and spurious IIR read in serial/8250.c
Date: Thu, 19 Feb 2009 19:37:53 +0100 [thread overview]
Message-ID: <87vdr6z30e.fsf@pike.pond.sub.org> (raw)
In-Reply-To: <18845.40059.190188.291643@mariner.uk.xensource.com> (Ian Jackson's message of "Thu\, 19 Feb 2009 17\:52\:59 +0000")
Ian Jackson <Ian.Jackson@eu.citrix.com> writes:
> 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.
Correct.
> 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.
Patch makes sense to me.
Acked-by: Markus Armbruster <armbru@redhat.com>
next prev parent reply other threads:[~2009-02-19 18:39 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-05 2:23 Serial console hangs with Linux 2.6.20 HVM guest Anders Kaseorg
2009-02-05 17:04 ` Ian Jackson
2009-02-05 19:34 ` Anders Kaseorg
2009-02-05 21:52 ` Anders Kaseorg
2009-02-10 15:34 ` Ian Jackson
2009-02-10 18:20 ` Anders Kaseorg
2009-02-11 16:08 ` [PATCH] IRQ handling race and spurious IIR read in serial/8250.c Ian Jackson
2009-02-19 17:52 ` Ian Jackson
2009-02-19 17:52 ` Ian Jackson
2009-02-19 18:37 ` Markus Armbruster [this message]
2009-02-19 18:37 ` Markus Armbruster
2009-02-19 19:24 ` Jeremy Fitzhardinge
2009-02-09 17:57 ` Serial console hangs with Linux 2.6.20 HVM guest Ian Jackson
2009-02-09 18:13 ` Anders Kaseorg
-- strict thread matches above, loose matches on Subject: below --
2009-03-12 17:57 [PATCH] IRQ handling race and spurious IIR read in serial/8250.c Markus Armbruster
2009-03-12 18:09 ` Alan Cox
2009-03-12 19:30 ` Ian Jackson
2009-03-12 21:38 ` [Xen-devel] " Alan Cox
2009-06-19 1:39 ` Robert Evans
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