From patchwork Mon Jun 24 12:42:53 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Raghavendra K T X-Patchwork-Id: 2771181 Return-Path: X-Original-To: patchwork-kvm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork1.web.kernel.org (Postfix) with ESMTP id D15259F245 for ; Mon, 24 Jun 2013 12:43:34 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 98C7120227 for ; Mon, 24 Jun 2013 12:43:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3E0AF201F6 for ; Mon, 24 Jun 2013 12:43:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753069Ab3FXMjF (ORCPT ); Mon, 24 Jun 2013 08:39:05 -0400 Received: from e28smtp02.in.ibm.com ([122.248.162.2]:54847 "EHLO e28smtp02.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753157Ab3FXMjB (ORCPT ); Mon, 24 Jun 2013 08:39:01 -0400 Received: from /spool/local by e28smtp02.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Mon, 24 Jun 2013 18:01:04 +0530 Received: from d28relay05.in.ibm.com (d28relay05.in.ibm.com [9.184.220.62]) by d28dlp02.in.ibm.com (Postfix) with ESMTP id 55570394004E; Mon, 24 Jun 2013 18:08:56 +0530 (IST) Received: from d28av03.in.ibm.com (d28av03.in.ibm.com [9.184.220.65]) by d28relay05.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r5OCcq7E28770520; Mon, 24 Jun 2013 18:08:53 +0530 Received: from d28av03.in.ibm.com (loopback [127.0.0.1]) by d28av03.in.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r5OCcrgi027674; Mon, 24 Jun 2013 22:38:56 +1000 Received: from codeblue.in.ibm.com (codeblue.in.ibm.com [9.124.158.47]) by d28av03.in.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id r5OCcqFJ027603; Mon, 24 Jun 2013 22:38:52 +1000 From: Raghavendra K T To: , , , , , , Cc: linux-doc@vger.kernel.org, , Raghavendra K T , , , , , , , , , , , , , , , , , , , , Date: Mon, 24 Jun 2013 18:12:53 +0530 Message-Id: <20130624124253.27508.60260.sendpatchset@codeblue.in.ibm.com> In-Reply-To: <20130624124014.27508.8906.sendpatchset@codeblue.in.ibm.com> References: <20130624124014.27508.8906.sendpatchset@codeblue.in.ibm.com> Subject: [PATCH RFC V10 11/18] xen/pvticketlock: Allow interrupts to be enabled while blocking X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13062412-5816-0000-0000-0000089A6285 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Spam-Status: No, score=-8.0 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP xen/pvticketlock: Allow interrupts to be enabled while blocking From: Jeremy Fitzhardinge If interrupts were enabled when taking the spinlock, we can leave them enabled while blocking to get the lock. If we can enable interrupts while waiting for the lock to become available, and we take an interrupt before entering the poll, and the handler takes a spinlock which ends up going into the slow state (invalidating the per-cpu "lock" and "want" values), then when the interrupt handler returns the event channel will remain pending so the poll will return immediately, causing it to return out to the main spinlock loop. Signed-off-by: Jeremy Fitzhardinge Reviewed-by: Konrad Rzeszutek Wilk Signed-off-by: Raghavendra K T --- arch/x86/xen/spinlock.c | 46 ++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 40 insertions(+), 6 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c index 3ebabde..2b012a5 100644 --- a/arch/x86/xen/spinlock.c +++ b/arch/x86/xen/spinlock.c @@ -140,7 +140,20 @@ static void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want) * partially setup state. */ local_irq_save(flags); - + /* + * We don't really care if we're overwriting some other + * (lock,want) pair, as that would mean that we're currently + * in an interrupt context, and the outer context had + * interrupts enabled. That has already kicked the VCPU out + * of xen_poll_irq(), so it will just return spuriously and + * retry with newly setup (lock,want). + * + * The ordering protocol on this is that the "lock" pointer + * may only be set non-NULL if the "want" ticket is correct. + * If we're updating "want", we must first clear "lock". + */ + w->lock = NULL; + smp_wmb(); w->want = want; smp_wmb(); w->lock = lock; @@ -155,24 +168,43 @@ static void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want) /* Only check lock once pending cleared */ barrier(); - /* Mark entry to slowpath before doing the pickup test to make - sure we don't deadlock with an unlocker. */ + /* + * Mark entry to slowpath before doing the pickup test to make + * sure we don't deadlock with an unlocker. + */ __ticket_enter_slowpath(lock); - /* check again make sure it didn't become free while - we weren't looking */ + /* + * check again make sure it didn't become free while + * we weren't looking + */ if (ACCESS_ONCE(lock->tickets.head) == want) { add_stats(TAKEN_SLOW_PICKUP, 1); goto out; } + + /* Allow interrupts while blocked */ + local_irq_restore(flags); + + /* + * If an interrupt happens here, it will leave the wakeup irq + * pending, which will cause xen_poll_irq() to return + * immediately. + */ + /* Block until irq becomes pending (or perhaps a spurious wakeup) */ xen_poll_irq(irq); add_stats(TAKEN_SLOW_SPURIOUS, !xen_test_irq_pending(irq)); + + local_irq_save(flags); + kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq)); out: cpumask_clear_cpu(cpu, &waiting_cpus); w->lock = NULL; + local_irq_restore(flags); + spin_time_accum_blocked(start); } PV_CALLEE_SAVE_REGS_THUNK(xen_lock_spinning); @@ -186,7 +218,9 @@ static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next) for_each_cpu(cpu, &waiting_cpus) { const struct xen_lock_waiting *w = &per_cpu(lock_waiting, cpu); - if (w->lock == lock && w->want == next) { + /* Make sure we read lock before want */ + if (ACCESS_ONCE(w->lock) == lock && + ACCESS_ONCE(w->want) == next) { add_stats(RELEASED_SLOW_KICKED, 1); xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR); break;