From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH v2] xen: arm: increase priority of SGIs used as IPIs Date: Mon, 17 Mar 2014 12:11:11 +0000 Message-ID: <5326E65F.5050101@linaro.org> References: <1395055862-23455-1-git-send-email-ian.campbell@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1395055862-23455-1-git-send-email-ian.campbell@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: Oleksandr Tyshchenko , stefano.stabellini@eu.citrix.com, tim@xen.org, xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org Hi Ian, On 03/17/2014 11:31 AM, Ian Campbell wrote: > Code such as on_selected_cpus expects/requires that an IPI can preempt a > processor which is just handling a normal interrupt. Lacking this property can > result in a deadlock between two CPUs trying to IPI each other from interrupt > context. > > For the time being there is only two priorities, IRQ and IPI, although it is > also conceivable that in the future some IPIs might be higher priority than > others. This could be used to implement a better BUG() than we have now, but I > haven't tackled that yet. > > Tested with a debug patch which sends a local IPI from a keyhandler, which is > run in serial interrupt context. > > This should also fix the issue reported by Oleksandr in "xen/arm: > maintenance_interrupt SMP fix" without resorting to trylock. Sorry, I didn't notice it before. If you plan to keep the last paragraph, can you add a link to the patch? Regards, -- Julien Grall