Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752842AbaATDj5 (ORCPT ); Sun, 19 Jan 2014 22:39:57 -0500 Received: from e35.co.us.ibm.com ([32.97.110.153]:33255 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752710AbaATDjz (ORCPT ); Sun, 19 Jan 2014 22:39:55 -0500 Date: Sun, 19 Jan 2014 19:39:47 -0800 From: "Paul E. McKenney" To: Waiman Long Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Arnd Bergmann , linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , Steven Rostedt , Andrew Morton , Michel Lespinasse , Andi Kleen , Rik van Riel , Linus Torvalds , Raghavendra K T , George Spelvin , Tim Chen , "Aswin Chandramouleeswaran\"" , Scott J Norton Subject: Re: [PATCH v9 4/5] qrwlock: Use smp_store_release() in write_unlock() Message-ID: <20140120033947.GA668@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1389761047-47566-1-git-send-email-Waiman.Long@hp.com> <1389761047-47566-5-git-send-email-Waiman.Long@hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1389761047-47566-5-git-send-email-Waiman.Long@hp.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14012003-6688-0000-0000-000005B21D5A Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 14, 2014 at 11:44:06PM -0500, Waiman Long wrote: > This patch modifies the queue_write_unlock() function to use the new > smp_store_release() function (currently in tip). It also removes the > temporary implementation of smp_load_acquire() and smp_store_release() > function in qrwlock.c. > > This patch will use atomic subtraction instead if the writer field is > not atomic. > > Signed-off-by: Waiman Long Reviewed-by: Paul E. McKenney > --- > include/asm-generic/qrwlock.h | 10 ++++++---- > kernel/locking/qrwlock.c | 34 ---------------------------------- > 2 files changed, 6 insertions(+), 38 deletions(-) > > diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h > index 5abb6ca..68f488b 100644 > --- a/include/asm-generic/qrwlock.h > +++ b/include/asm-generic/qrwlock.h > @@ -181,11 +181,13 @@ static inline void queue_read_unlock(struct qrwlock *lock) > static inline void queue_write_unlock(struct qrwlock *lock) > { > /* > - * Make sure that none of the critical section will be leaked out. > + * If the writer field is atomic, it can be cleared directly. > + * Otherwise, an atomic subtraction will be used to clear it. > */ > - smp_mb__before_clear_bit(); > - ACCESS_ONCE(lock->cnts.writer) = 0; > - smp_mb__after_clear_bit(); > + if (__native_word(lock->cnts.writer)) > + smp_store_release(&lock->cnts.writer, 0); > + else > + atomic_sub(_QW_LOCKED, &lock->cnts.rwa); > } > > /* > diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c > index 053be4d..2727188 100644 > --- a/kernel/locking/qrwlock.c > +++ b/kernel/locking/qrwlock.c > @@ -47,40 +47,6 @@ > # define arch_mutex_cpu_relax() cpu_relax() > #endif > > -#ifndef smp_load_acquire > -# ifdef CONFIG_X86 > -# define smp_load_acquire(p) \ > - ({ \ > - typeof(*p) ___p1 = ACCESS_ONCE(*p); \ > - barrier(); \ > - ___p1; \ > - }) > -# else > -# define smp_load_acquire(p) \ > - ({ \ > - typeof(*p) ___p1 = ACCESS_ONCE(*p); \ > - smp_mb(); \ > - ___p1; \ > - }) > -# endif > -#endif > - > -#ifndef smp_store_release > -# ifdef CONFIG_X86 > -# define smp_store_release(p, v) \ > - do { \ > - barrier(); \ > - ACCESS_ONCE(*p) = v; \ > - } while (0) > -# else > -# define smp_store_release(p, v) \ > - do { \ > - smp_mb(); \ > - ACCESS_ONCE(*p) = v; \ > - } while (0) > -# endif > -#endif > - > /* > * If an xadd (exchange-add) macro isn't available, simulate one with > * the atomic_add_return() function. > -- > 1.7.1 > -- 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/