Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753554AbbBPQrS (ORCPT ); Mon, 16 Feb 2015 11:47:18 -0500 Received: from mail-we0-f179.google.com ([74.125.82.179]:46410 "EHLO mail-we0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752986AbbBPQrR (ORCPT ); Mon, 16 Feb 2015 11:47:17 -0500 Message-ID: <54E21F10.1040402@cantab.net> Date: Mon, 16 Feb 2015 16:47:12 +0000 From: David Vrabel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.4.0 MIME-Version: 1.0 To: Raghavendra K T , tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, peterz@infradead.org, torvalds@linux-foundation.org, konrad.wilk@oracle.com, pbonzini@redhat.com CC: waiman.long@hp.com, jeremy@goop.org, ak@linux.intel.com, a.ryabinin@samsung.com, kvm@vger.kernel.org, borntraeger@de.ibm.com, jasowang@redhat.com, x86@kernel.org, oleg@redhat.com, linux-kernel@vger.kernel.org, paul.gortmaker@windriver.com, dave@stgolabs.net, xen-devel@lists.xenproject.org, davej@redhat.com, akpm@linux-foundation.org, paulmck@linux.vnet.ibm.com, virtualization@lists.linux-foundation.org, sasha.levin@oracle.com Subject: Re: [Xen-devel] [PATCH V5] x86 spinlock: Fix memory corruption on completing completions References: <1423979744-18320-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com> <20150215173043.GA7471@linux.vnet.ibm.com> In-Reply-To: <20150215173043.GA7471@linux.vnet.ibm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2184 Lines: 61 On 15/02/15 17:30, Raghavendra K T wrote: > --- a/arch/x86/xen/spinlock.c > +++ b/arch/x86/xen/spinlock.c > @@ -41,7 +41,7 @@ static u8 zero_stats; > static inline void check_zero(void) > { > u8 ret; > - u8 old = ACCESS_ONCE(zero_stats); > + u8 old = READ_ONCE(zero_stats); > if (unlikely(old)) { > ret = cmpxchg(&zero_stats, old, 0); > /* This ensures only one fellow resets the stat */ > @@ -112,6 +112,7 @@ __visible void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want) > struct xen_lock_waiting *w = this_cpu_ptr(&lock_waiting); > int cpu = smp_processor_id(); > u64 start; > + __ticket_t head; > unsigned long flags; > > /* If kicker interrupts not initialized yet, just spin */ > @@ -159,11 +160,15 @@ __visible void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want) > */ > __ticket_enter_slowpath(lock); > > + /* make sure enter_slowpath, which is atomic does not cross the read */ > + smp_mb__after_atomic(); > + > /* > * check again make sure it didn't become free while > * we weren't looking > */ > - if (ACCESS_ONCE(lock->tickets.head) == want) { > + head = READ_ONCE(lock->tickets.head); > + if (__tickets_equal(head, want)) { > add_stats(TAKEN_SLOW_PICKUP, 1); > goto out; > } > @@ -204,8 +209,8 @@ static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next) > const struct xen_lock_waiting *w = &per_cpu(lock_waiting, cpu); > > /* Make sure we read lock before want */ > - if (ACCESS_ONCE(w->lock) == lock && > - ACCESS_ONCE(w->want) == next) { > + if (READ_ONCE(w->lock) == lock && > + READ_ONCE(w->want) == next) { > add_stats(RELEASED_SLOW_KICKED, 1); > xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR); > break; Acked-by: David Vrabel Although some of the ACCESS_ONCE to READ_ONCE changes are cosmetic and are perhaps best left out of a patch destined for stable. David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/