Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2993002AbbEOXRj (ORCPT ); Fri, 15 May 2015 19:17:39 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:43338 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2992866AbbEOXPE (ORCPT ); Fri, 15 May 2015 19:15:04 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tahsin Erdogan , peterz@infradead.org, Waiman.Long@hp.com, borntraeger@de.ibm.com, oleg@redhat.com, raghavendra.kt@linux.vnet.ibm.com, Thomas Gleixner Subject: [PATCH 4.0 01/60] x86/spinlocks: Fix regression in spinlock contention detection Date: Fri, 15 May 2015 16:14:02 -0700 Message-Id: <20150515231018.860323482@linuxfoundation.org> X-Mailer: git-send-email 2.4.0 In-Reply-To: <20150515231018.815421141@linuxfoundation.org> References: <20150515231018.815421141@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1912 Lines: 51 4.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tahsin Erdogan commit e8a4a2696fecb398b0288c43c0e0dbb91e265bb2 upstream. 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 Cc: peterz@infradead.org Cc: Waiman.Long@hp.com Cc: borntraeger@de.ibm.com Cc: oleg@redhat.com Cc: raghavendra.kt@linux.vnet.ibm.com Link: http://lkml.kernel.org/r/1430799331-20445-1-git-send-email-tahsin@google.com Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/spinlock.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- 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 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 -- 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/