From patchwork Wed Apr 9 14:30:57 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Stefan Bader X-Patchwork-Id: 337857 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from huckleberry.canonical.com (huckleberry.canonical.com [91.189.94.19]) by ozlabs.org (Postfix) with ESMTP id 6B434140151; Thu, 10 Apr 2014 00:31:12 +1000 (EST) Received: from localhost ([127.0.0.1] helo=huckleberry.canonical.com) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1WXtWr-00044O-7k; Wed, 09 Apr 2014 14:31:05 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1WXtWl-00042M-4C for kernel-team@lists.ubuntu.com; Wed, 09 Apr 2014 14:30:59 +0000 Received: from hsi-kbw-46-223-71-61.hsi.kabel-badenwuerttemberg.de ([46.223.71.61] helo=[192.168.2.5]) by youngberry.canonical.com with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1WXtWl-0002sc-1z for kernel-team@lists.ubuntu.com; Wed, 09 Apr 2014 14:30:59 +0000 Message-ID: <534559A1.2050603@canonical.com> Date: Wed, 09 Apr 2014 16:30:57 +0200 From: Stefan Bader User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: Ubuntu Kernel Team Subject: Fwd: [PATCH -stable] x86,preempt: Fix preemption for i386 References: <20140409142447.GD13658@twins.programming.kicks-ass.net> In-Reply-To: <20140409142447.GD13658@twins.programming.kicks-ass.net> X-Enigmail-Version: 1.5.2 X-Forwarded-Message-Id: <20140409142447.GD13658@twins.programming.kicks-ass.net> X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.14 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: kernel-team-bounces@lists.ubuntu.com If that one gets accepted into upstream stable and comes back to Trusty we can drop my SAUCE patch that added the preempt folding to kvm. "UBUNTU: SAUCE: kvm: Force preempt folding in kvm on i386" -Stefan -------- Original Message -------- Subject: [PATCH -stable] x86,preempt: Fix preemption for i386 Date: Wed, 9 Apr 2014 16:24:47 +0200 From: Peter Zijlstra To: Stefan Bader CC: Toralf Förster , Michele Ballabio , linux-kernel@vger.kernel.org, fweisbec@gmail.com, mingo@kernel.org, Steven Rostedt , David Cohen , Paolo Bonzini , Borislav Petkov , Linus Torvalds , Greg KH Greg, Linus, I'm not entirely clear on how acceptable it is to propose a different patch for -stable than what we have upstream. The below Changelog explain, but in short, we should either backport 4 rather invasive patches to .13-stable and .14-stable or do the small patch provided. The 4 patches by Steven are the right thing to do, but I feel they might be too invasive to propose for -stable, therefore the alternative approach. --- Subject: x86,preempt: Fix preemption for i386 From: Peter Zijlstra Date: Tue, 8 Apr 2014 14:21:28 +0200 Many people reported preemption/reschedule problems with i386 kernels for .13 and .14. After Michele bisected this to a combination of 3e8e42c69bb ("sched: Revert need_resched() to look at TIF_NEED_RESCHED") ded79754754 ("irq: Force hardirq exit's softirq processing on its own stack") it finally dawned on me that i386's current_thread_info() was to blame. When we are on interrupt/exception stacks, we fail to observe the right TIF_NEED_RESCHED bit and therefore the PREEMPT_NEED_RESCHED folding malfunctions. Current upstream fixes this by making i386 behave the same as x86_64 already did: 2432e1364bbe ("x86: Nuke the supervisor_stack field in i386 thread_info") b807902a88c4 ("x86: Nuke GET_THREAD_INFO_WITH_ESP() macro for i386") 0788aa6a23cb ("x86: Prepare removal of previous_esp from i386 thread_info structure") 198d208df437 ("x86: Keep thread_info on thread stack in x86_32") However, that is far too much to stuff into -stable. Therefore I propose we merge the below patch which uses task_thread_info(current) for tif_need_resched() instead of the ESP based current_thread_info(). This makes sure we always observe the one true TIF_NEED_RESCHED bit and things will work as expected again. Cc: fweisbec@gmail.com Cc: mingo@kernel.org Cc: Steven Rostedt Cc: David Cohen Cc: Paolo Bonzini Cc: Borislav Petkov Tested-by: Stefan Bader Tested-by: Toralf Förster Tested-by: Michele Ballabio Signed-off-by: Peter Zijlstra --- arch/x86/include/asm/preempt.h | 11 +++++++++++ include/linux/preempt.h | 4 ++++ include/linux/thread_info.h | 2 -- 3 files changed, 15 insertions(+), 2 deletions(-) --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -5,6 +5,17 @@ #include #include +#ifdef CONFIG_X86_32 +/* + * i386's current_thread_info() depends on ESP and for interrupt/exception + * stacks this doesn't yield the actual task thread_info. + * + * We hard rely on the fact that all the TIF_NEED_RESCHED bits are + * the same, therefore use the slightly more expensive version below. + */ +#define tif_need_resched() test_tsk_thread_flag(current, TIF_NEED_RESCHED) +#endif + DECLARE_PER_CPU(int, __preempt_count); /* --- a/include/linux/preempt.h +++ b/include/linux/preempt.h @@ -17,6 +17,10 @@ #include +#ifndef tif_need_resched +#define tif_need_resched() test_thread_flag(TIF_NEED_RESCHED) +#endif + #if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER) extern void preempt_count_add(int val); extern void preempt_count_sub(int val); --- a/include/linux/thread_info.h +++ b/include/linux/thread_info.h @@ -118,8 +118,6 @@ static inline __deprecated void set_need */ } -#define tif_need_resched() test_thread_flag(TIF_NEED_RESCHED) - #if defined TIF_RESTORE_SIGMASK && !defined HAVE_SET_RESTORE_SIGMASK /* * An arch can define its own version of set_restore_sigmask() to get the