From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pan Xinhui Subject: [PATCH v3] locking/qrwlock: Let qrwlock has same layout regardless of the endian Date: Mon, 20 Jun 2016 14:20:52 +0800 Message-ID: <1466403652-2931-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> Return-path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:57795 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752515AbcFTGVT (ORCPT ); Mon, 20 Jun 2016 02:21:19 -0400 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.11/8.16.0.11) with SMTP id u5K6JW9Y100986 for ; Mon, 20 Jun 2016 02:21:18 -0400 Received: from e32.co.us.ibm.com (e32.co.us.ibm.com [32.97.110.150]) by mx0b-001b2d01.pphosted.com with ESMTP id 23mywvecf2-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 20 Jun 2016 02:21:17 -0400 Received: from localhost by e32.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 20 Jun 2016 00:21:16 -0600 Sender: linux-arch-owner@vger.kernel.org List-ID: To: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org Cc: mingo@redhat.com, peterz@infradead.org, arnd@arndb.de, Waiman.Long@hpe.com, Pan Xinhui This patch aims to get rid of endianness in queued_write_unlock(). We want to set __qrwlock->wmode to NULL, however the address is not &lock->cnts in big endian machine. That causes queued_write_unlock() write NULL to the wrong field of __qrwlock. Actually qrwlock can have same layout, IOW we can remove the #if __little_endian in struct __qrwlock. With such modification, we only need define some _QW* and _QR* with corresponding values in different endian systems. Suggested-by: Will Deacon Signed-off-by: Pan Xinhui Acked-by: Waiman Long --- change from v2: change macro's name, add comments. change from v1: A typo fix which is really bad... thanks Will for the carefull review. :) --- include/asm-generic/qrwlock.h | 15 +++++++++++---- kernel/locking/qrwlock.c | 11 +++++------ 2 files changed, 16 insertions(+), 10 deletions(-) diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h index 54a8e65..28fb94a 100644 --- a/include/asm-generic/qrwlock.h +++ b/include/asm-generic/qrwlock.h @@ -27,11 +27,18 @@ /* * Writer states & reader shift and bias */ -#define _QW_WAITING 1 /* A writer is waiting */ -#define _QW_LOCKED 0xff /* A writer holds the lock */ -#define _QW_WMASK 0xff /* Writer mask */ +#ifdef __LITTLE_ENDIAN #define _QR_SHIFT 8 /* Reader count shift */ -#define _QR_BIAS (1U << _QR_SHIFT) +#define _QW_SHIFT 0 /* Writer mode shift */ +#else +#define _QR_SHIFT 0 /* Reader count shift */ +#define _QW_SHIFT 24 /* Writer mode shift */ +#endif + +#define _QW_WAITING (1U << _QW_SHIFT) /* A writer is waiting */ +#define _QW_LOCKED (0xffU << _QW_SHIFT) /* A writer holds the lock */ +#define _QW_WMASK (0xffU << _QW_SHIFT) /* Writer mask */ +#define _QR_BIAS (1U << _QR_SHIFT) /* * External function declarations diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c index fec0823..0502e3a 100644 --- a/kernel/locking/qrwlock.c +++ b/kernel/locking/qrwlock.c @@ -30,18 +30,16 @@ struct __qrwlock { union { atomic_t cnts; struct { -#ifdef __LITTLE_ENDIAN u8 wmode; /* Writer mode */ u8 rcnts[3]; /* Reader counts */ -#else - u8 rcnts[3]; /* Reader counts */ - u8 wmode; /* Writer mode */ -#endif }; }; arch_spinlock_t lock; }; +/* get the value of wmode when cnts is v */ +#define _QW_BYTEVAL(v) ((v) >> _QW_SHIFT) + /** * rspin_until_writer_unlock - inc reader count & spin until writer is gone * @lock : Pointer to queue rwlock structure @@ -127,7 +125,8 @@ void queued_write_lock_slowpath(struct qrwlock *lock) struct __qrwlock *l = (struct __qrwlock *)lock; if (!READ_ONCE(l->wmode) && - (cmpxchg_relaxed(&l->wmode, 0, _QW_WAITING) == 0)) + (cmpxchg_relaxed(&l->wmode, 0, + _QW_BYTEVAL(_QW_WAITING)) == 0)) break; cpu_relax_lowlatency(); -- 1.9.1