From: Anton Vorontsov <anton.vorontsov@linaro.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Russell King" <linux@arm.linux.org.uk>,
"Jason Wessel" <jason.wessel@windriver.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Alan Cox" <alan@linux.intel.com>,
"Arve Hjønnevåg" <arve@android.com>,
"Colin Cross" <ccross@android.com>,
"Brian Swetland" <swetland@google.com>,
"John Stultz" <john.stultz@linaro.org>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linaro-kernel@lists.linaro.org, patches@linaro.org,
kernel-team@android.com, kgdb-bugreport@lists.sourceforge.net,
linux-serial@vger.kernel.org
Subject: Re: [PATCH 08/14] tty/serial/kgdboc: Add and wire up clear_irqs callback
Date: Mon, 10 Sep 2012 10:57:04 -0700 [thread overview]
Message-ID: <20120910175704.GA11392@lizard> (raw)
In-Reply-To: <20120910121624.226c1a88@pyramind.ukuu.org.uk>
On Mon, Sep 10, 2012 at 12:16:24PM +0100, Alan Cox wrote:
> > serial port, the CPU receives NMI exception, and we fall into KDB
> > shell. So, it is our "debug console", and it is able to interrupt
> > (and thus debug) even IRQ handlers themselves.
>
> You seem to have an assumption of single core here. What happens if
> the NMI hits CPU #0 and the serial IRQ hits CPU #1 simultaneously ?
If you can't redirect all serial IRQs to NMI context, e.g. sometimes you get
NMIs, sometimes IRQs, then your NMI handling is not deterministic, and surely
this is not supported.
The whole concept of clearing IRQs is needed if serial IRQ is routed to the
NMI/FIQ (on all CPUs), which by definition guarantees that serial IRQ routine
is never triggered. We "steal" all and every serial port's IRQs.
Thanks!
WARNING: multiple messages have this Message-ID (diff)
From: anton.vorontsov@linaro.org (Anton Vorontsov)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 08/14] tty/serial/kgdboc: Add and wire up clear_irqs callback
Date: Mon, 10 Sep 2012 10:57:04 -0700 [thread overview]
Message-ID: <20120910175704.GA11392@lizard> (raw)
In-Reply-To: <20120910121624.226c1a88@pyramind.ukuu.org.uk>
On Mon, Sep 10, 2012 at 12:16:24PM +0100, Alan Cox wrote:
> > serial port, the CPU receives NMI exception, and we fall into KDB
> > shell. So, it is our "debug console", and it is able to interrupt
> > (and thus debug) even IRQ handlers themselves.
>
> You seem to have an assumption of single core here. What happens if
> the NMI hits CPU #0 and the serial IRQ hits CPU #1 simultaneously ?
If you can't redirect all serial IRQs to NMI context, e.g. sometimes you get
NMIs, sometimes IRQs, then your NMI handling is not deterministic, and surely
this is not supported.
The whole concept of clearing IRQs is needed if serial IRQ is routed to the
NMI/FIQ (on all CPUs), which by definition guarantees that serial IRQ routine
is never triggered. We "steal" all and every serial port's IRQs.
Thanks!
next prev parent reply other threads:[~2012-09-10 17:59 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-10 4:08 [PATCH v5 0/14] KGDB/KDB FIQ (NMI) debugger Anton Vorontsov
2012-09-10 4:08 ` Anton Vorontsov
2012-09-10 4:11 ` [PATCH 01/14] serial/amba-pl011: fix ages old copy-paste errors Anton Vorontsov
2012-09-10 4:11 ` Anton Vorontsov
2012-09-10 4:12 ` [PATCH 02/14] drivers/tty/serial/amba-pl0{10,11}.c: use clk_prepare_enable and clk_disable_unprepare Anton Vorontsov
2012-09-10 4:12 ` Anton Vorontsov
2012-09-10 4:12 ` [PATCH 03/14] kernel/debug: Mask KGDB NMI upon entry Anton Vorontsov
2012-09-10 4:12 ` Anton Vorontsov
2012-09-10 4:13 ` [PATCH 04/14] kdb: Implement disable_nmi command Anton Vorontsov
2012-09-10 4:13 ` Anton Vorontsov
2012-09-10 4:13 ` [PATCH 05/14] kdb: Turn KGDB_KDB=n stubs into static inlines Anton Vorontsov
2012-09-10 4:13 ` Anton Vorontsov
2012-09-10 4:13 ` [PATCH 06/14] tty/serial/core: Introduce poll_init callback Anton Vorontsov
2012-09-10 4:13 ` Anton Vorontsov
2012-09-10 11:13 ` Alan Cox
2012-09-10 11:13 ` Alan Cox
2012-09-10 17:57 ` Anton Vorontsov
2012-09-10 17:57 ` Anton Vorontsov
2012-09-10 19:18 ` Alan Cox
2012-09-10 19:18 ` Alan Cox
2012-09-10 4:13 ` [PATCH 07/14] tty/serial/amba-pl011: Implement " Anton Vorontsov
2012-09-10 4:13 ` Anton Vorontsov
2012-09-10 4:13 ` [PATCH 08/14] tty/serial/kgdboc: Add and wire up clear_irqs callback Anton Vorontsov
2012-09-10 4:13 ` Anton Vorontsov
2012-09-10 11:16 ` Alan Cox
2012-09-10 11:16 ` Alan Cox
2012-09-10 17:57 ` Anton Vorontsov [this message]
2012-09-10 17:57 ` Anton Vorontsov
2012-09-10 19:19 ` Alan Cox
2012-09-10 19:19 ` Alan Cox
2012-09-10 20:13 ` Anton Vorontsov
2012-09-10 20:13 ` Anton Vorontsov
2012-09-10 4:14 ` [PATCH 09/14] tty/serial/amba-pl011: Implement " Anton Vorontsov
2012-09-10 4:14 ` Anton Vorontsov
2012-09-10 11:17 ` Alan Cox
2012-09-10 11:17 ` Alan Cox
2012-09-10 17:56 ` Anton Vorontsov
2012-09-10 17:56 ` Anton Vorontsov
2012-09-10 4:14 ` [PATCH 10/14] tty/serial: Add kgdb_nmi driver Anton Vorontsov
2012-09-10 4:14 ` Anton Vorontsov
2012-09-10 11:11 ` Alan Cox
2012-09-10 11:11 ` Alan Cox
2012-09-10 17:54 ` Anton Vorontsov
2012-09-10 17:54 ` Anton Vorontsov
2012-09-10 4:14 ` [PATCH 11/14] ARM: Move some macros from entry-armv to entry-header Anton Vorontsov
2012-09-10 4:14 ` Anton Vorontsov
2012-09-10 4:14 ` [PATCH 12/14] ARM: Add KGDB/KDB FIQ debugger generic code Anton Vorontsov
2012-09-10 4:14 ` Anton Vorontsov
2012-09-10 4:14 ` [PATCH 13/14] ARM: VIC: Add a couple of low-level FIQ management helpers Anton Vorontsov
2012-09-10 4:14 ` Anton Vorontsov
2012-09-10 4:14 ` [PATCH 14/14] ARM: versatile: Make able to use UART ports for KGDB FIQ debugger Anton Vorontsov
2012-09-10 4:14 ` Anton Vorontsov
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