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From: peterz@infradead.org
To: Sumit Garg <sumit.garg@linaro.org>
Cc: Doug Anderson <dianders@chromium.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Daniel Thompson <daniel.thompson@linaro.org>,
	linux-serial@vger.kernel.org,
	kgdb-bugreport@lists.sourceforge.net,
	Jiri Slaby <jslaby@suse.com>,
	Russell King - ARM Linux <linux@armlinux.org.uk>,
	Jason Wessel <jason.wessel@windriver.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC 1/5] tty/sysrq: Make sysrq handler NMI aware
Date: Fri, 14 Aug 2020 16:34:00 +0200	[thread overview]
Message-ID: <20200814143400.GB165568@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAFA6WYMy_+RdsPJekm7zmCrFUXHqjsfr3JvyD7L8A2X8+jB8Qw@mail.gmail.com>

On Fri, Aug 14, 2020 at 12:54:35PM +0530, Sumit Garg wrote:
> On Thu, 13 Aug 2020 at 05:30, Doug Anderson <dianders@chromium.org> wrote:
> > On Tue, Jul 21, 2020 at 5:10 AM Sumit Garg <sumit.garg@linaro.org> wrote:
> > Wishful thinking, but (as far as I can tell) irq_work_queue() only
> > queues work on the CPU running the NMI.  I don't have lots of NMI
> > experience, but any chance there is a variant that will queue work on
> > any CPU?  Then sysrq handlers that aren't NMI aware will be more
> > likely to work.
> >
> 
> Unfortunately, queuing work on other CPUs isn't safe in NMI context,
> see this warning [1]. The comment mentions:
> 
> /* Arch remote IPI send/receive backend aren't NMI safe */
> 
> Peter,
> 
> Can you throw some light here as to why it isn't considered NMI-safe
> to send remote IPI in NMI context? Is it an arch specific limitation?

Yeah, remote irq_work uses __smp_call_single_queue() /
send_call_function_single_ipi() which isn't safe to be used from NMI
context in general.

arch_irq_work_raise() is very carefully implemented on a number of
platforms to be able to (self) IPI from NMI context.


  reply	other threads:[~2020-08-14 14:34 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-21 12:10 [RFC 0/5] Introduce NMI aware serial drivers Sumit Garg
2020-07-21 12:10 ` [RFC 1/5] tty/sysrq: Make sysrq handler NMI aware Sumit Garg
2020-08-12 23:59   ` Doug Anderson
2020-08-14  7:24     ` Sumit Garg
2020-08-14 14:34       ` peterz [this message]
2020-08-14 14:57       ` Doug Anderson
2020-08-17 14:08         ` Sumit Garg
2020-08-17 17:19           ` Doug Anderson
2020-08-18 13:30             ` Sumit Garg
2020-07-21 12:10 ` [RFC 2/5] serial: core: Add framework to allow NMI aware serial drivers Sumit Garg
2020-08-12 23:59   ` Doug Anderson
2020-08-13 14:19     ` Sumit Garg
2020-08-13 14:37       ` Doug Anderson
2020-08-14 11:17         ` Sumit Garg
2020-08-14 14:13           ` Daniel Thompson
2020-08-17 12:27             ` Sumit Garg
2020-08-17 13:57               ` Doug Anderson
2020-08-17 14:23                 ` Sumit Garg
2020-08-17 14:32                   ` Daniel Thompson
2020-08-18 13:18                     ` Sumit Garg
2020-08-17 14:28               ` Daniel Thompson
2020-08-18 13:06                 ` Sumit Garg
2020-08-14 14:43           ` Doug Anderson
2020-08-17 12:29             ` Sumit Garg
2020-07-21 12:10 ` [RFC 3/5] serial: amba-pl011: Re-order APIs definition Sumit Garg
2020-07-21 12:10 ` [RFC 4/5] serial: amba-pl011: Enable NMI aware uart port Sumit Garg
2020-08-12 23:59   ` Doug Anderson
2020-08-13 10:34     ` Sumit Garg
2020-07-21 12:10 ` [RFC 5/5] serial: Remove KGDB NMI serial driver Sumit Garg
2020-08-11 13:50 ` [RFC 0/5] Introduce NMI aware serial drivers Sumit Garg
2020-08-11 13:58   ` Greg Kroah-Hartman
2020-08-11 14:29     ` Sumit Garg
2020-08-11 14:58       ` Greg Kroah-Hartman
2020-08-11 17:15         ` Doug Anderson
2020-08-12 14:52           ` Sumit Garg
2020-08-12 15:27             ` Doug Anderson
2020-08-13  0:08               ` Doug Anderson
2020-08-13  9:25                 ` Sumit Garg
2020-08-13 10:17                   ` Daniel Thompson
2020-08-14 12:06                     ` Sumit Garg
2020-08-14 14:18                       ` Daniel Thompson
2020-08-17  5:12                         ` Sumit Garg
2020-08-17  9:28                           ` Daniel Thompson
2020-08-17 14:12                             ` Sumit Garg
2020-08-13 15:26                   ` Doug Anderson
2020-08-14 12:50                     ` Sumit Garg
2020-08-12  5:48         ` Sumit Garg

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