From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753581AbbEEESD (ORCPT ); Tue, 5 May 2015 00:18:03 -0400 Received: from mail-oi0-f50.google.com ([209.85.218.50]:33329 "EHLO mail-oi0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752757AbbEEERx (ORCPT ); Tue, 5 May 2015 00:17:53 -0400 From: Tahsin Erdogan To: tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org Cc: peterz@infradead.org, Waiman.Long@hp.com, borntraeger@de.ibm.com, oleg@redhat.com, raghavendra.kt@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, Tahsin Erdogan Subject: [PATCH] x86/spinlocks: Fix regression in spinlock contention detection Date: Mon, 4 May 2015 21:15:31 -0700 Message-Id: <1430799331-20445-1-git-send-email-tahsin@google.com> X-Mailer: git-send-email 2.2.0.rc0.207.ga3a616c Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A spinlock is regarded as contended when there is at least one waiter. Currently, the code that checks whether there are any waiters rely on tail value being greater than head. However, this is not true if tail reaches the max value and wraps back to zero, so arch_spin_is_contended() incorrectly returns 0 (not contended) when tail is smaller than head. The original code (before regression) handled this case by casting the (tail - head) to an unsigned value. This change simply restores that behavior. Fixes: d6abfdb20223 ("x86/spinlocks/paravirt: Fix memory corruption on unlock") Signed-off-by: Tahsin Erdogan --- arch/x86/include/asm/spinlock.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h index cf87de3..64b6117 100644 --- a/arch/x86/include/asm/spinlock.h +++ b/arch/x86/include/asm/spinlock.h @@ -169,7 +169,7 @@ static inline int arch_spin_is_contended(arch_spinlock_t *lock) struct __raw_tickets tmp = READ_ONCE(lock->tickets); tmp.head &= ~TICKET_SLOWPATH_FLAG; - return (tmp.tail - tmp.head) > TICKET_LOCK_INC; + return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC; } #define arch_spin_is_contended arch_spin_is_contended -- 2.2.0.rc0.207.ga3a616c