From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751683Ab1LPLNp (ORCPT ); Fri, 16 Dec 2011 06:13:45 -0500 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:49932 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750981Ab1LPLNj (ORCPT ); Fri, 16 Dec 2011 06:13:39 -0500 Date: Fri, 16 Dec 2011 11:13:19 +0000 From: Catalin Marinas To: Peter Zijlstra Cc: "frank.rowand@am.sony.com" , "tglx@linutronix.de" , "linux-kernel@vger.kernel.org" , "rostedt@goodmis.org" Subject: Re: [PATCH] PREEMPT_RT_FULL: ARM context switch needs IRQs enabled Message-ID: <20111216111319.GB6342@arm.com> References: <4EEAB90D.3050504@am.sony.com> <1324029272.18942.73.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1324029272.18942.73.camel@twins> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 16, 2011 at 09:54:32AM +0000, Peter Zijlstra wrote: > On Thu, 2011-12-15 at 19:20 -0800, Frank Rowand wrote: > > ARMv6 and later have VIPT caches and the TLBs are tagged with an ASID > > (application specific ID). The number of ASIDs is limited to 256 and > > the allocation algorithm requires IPIs when all the ASIDs have been > > used. The IPIs require interrupts enabled during context switch for > > deadlock avoidance. > > > > The RT patch mm-protect-activate-switch-mm.patch disables irqs around > > activate_mm() and switch_mm(), which are the portion of the ARMv6 > > context switch that require interrupts enabled. > > > > The solution for the ARMv6 processors could be to _not_ disable irqs. > > A more conservative solution is to provide the same environment that > > the scheduler provides, that is preempt_disable(). This is more > > resilient for possible future changes to the ARM context switch code > > that is not aware of the RT patches. > > > > This patch will conflict slightly with Catalin's patch set to remove > > __ARCH_WANT_INTERRUPTS_ON_CTXSW, when that is accepted: > > > > http://lkml.indiana.edu/hypermail/linux/kernel/1111.3/01893.html > > > > When Catalin's patch set is accepted, this RT patch will need to reverse > > the change in patch 6 to arch/arm/include/asm/system.h: > > > We could just merge Catalin's stuff in -rt to give it a test ride and > see if anything horrible happens.. :-) Russell agreed for me to push this to -next (in case -rt uses that, not sure) to get a bit more exposure. Otherwise testing the patches in -rt would really help spotting bugs. But we need to sort out the dangling switch_mm() calls (without a corresponding post-switch hook call) that I mentioned in my reply to Frank. -- Catalin