Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752880AbbGAGef (ORCPT ); Wed, 1 Jul 2015 02:34:35 -0400 Received: from e19.ny.us.ibm.com ([129.33.205.209]:59303 "EHLO e19.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752764AbbGAGeZ (ORCPT ); Wed, 1 Jul 2015 02:34:25 -0400 X-Helo: d01dlp01.pok.ibm.com X-MailFrom: shreyas@linux.vnet.ibm.com X-RcptTo: linux-kernel@vger.kernel.org From: "Shreyas B. Prabhu" To: Paul Mackerras , Michael Ellerman Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, mahesh@linux.vnet.ibm.com, "Shreyas B. Prabhu" Subject: [PATCH] powerpc/powernv: Fix race in updating core_idle_state Date: Wed, 1 Jul 2015 12:04:10 +0530 Message-Id: <1435732450-7258-1-git-send-email-shreyas@linux.vnet.ibm.com> X-Mailer: git-send-email 1.9.3 X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15070106-0057-0000-0000-0000009A80D8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2608 Lines: 81 core_idle_state is maintained for each core. It uses 0-7 bits to track whether a thread in the core has entered fastsleep or winkle. 8th bit is used as a lock bit. The lock bit is set in these 2 scenarios- - The thread is first in subcore to wakeup from sleep/winkle. - If its the last thread in the core about to enter sleep/winkle While the lock bit is set, if any other thread in the core wakes up, it loops until the lock bit is cleared before proceeding in the wakeup path. This helps prevent race conditions w.r.t fastsleep workaround and prevents threads from switching to process context before core/subcore resources are restored. But, in the path to sleep/winkle entry, we currently don't check for lock-bit. This exposes us to following race when running with subcore on- First thread in the subcorea Another thread in the same waking up core entering sleep/winkle lwarx r15,0,r14 ori r15,r15,PNV_CORE_IDLE_LOCK_BIT stwcx. r15,0,r14 [Code to restore subcore state] lwarx r15,0,r14 [clear thread bit] stwcx. r15,0,r14 andi. r15,r15,PNV_CORE_IDLE_THREAD_BITS stw r15,0(r14) Here, after the thread entering sleep clears its thread bit in core_idle_state, the value is overwritten by the thread waking up. This patch fixes the above race by looping on the lock bit even while entering the idle states. Signed-off-by: Shreyas B. Prabhu --- arch/powerpc/kernel/idle_power7.S | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/arch/powerpc/kernel/idle_power7.S b/arch/powerpc/kernel/idle_power7.S index ccde8f0..48c7d4f 100644 --- a/arch/powerpc/kernel/idle_power7.S +++ b/arch/powerpc/kernel/idle_power7.S @@ -144,12 +144,26 @@ power7_enter_nap_mode: bge cr3,2f IDLE_STATE_ENTER_SEQ(PPC_NAP) /* No return */ + +core_idle_lock_held_entry: + HMT_LOW +core_idle_lock_loop_entry: + lwz r15,0(r14) + andi. r9,r15,PNV_CORE_IDLE_LOCK_BIT + bne core_idle_lock_loop_entry + HMT_MEDIUM + b lwarx_loop1 + 2: /* Sleep or winkle */ lbz r7,PACA_THREAD_MASK(r13) ld r14,PACA_CORE_IDLE_STATE_PTR(r13) lwarx_loop1: lwarx r15,0,r14 + + andi. r9,r15,PNV_CORE_IDLE_LOCK_BIT + bne core_idle_lock_held_entry + andc r15,r15,r7 /* Clear thread bit */ andi. r15,r15,PNV_CORE_IDLE_THREAD_BITS -- 1.9.3 -- 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/