From patchwork Thu Aug 2 18:29:39 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Bart Van Assche X-Patchwork-Id: 10554047 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 9E945174A for ; Thu, 2 Aug 2018 18:29:47 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 90EE22C465 for ; Thu, 2 Aug 2018 18:29:47 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 85B242C46C; Thu, 2 Aug 2018 18:29:47 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.8 required=2.0 tests=BAYES_00,DKIM_SIGNED, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id E38502C465 for ; Thu, 2 Aug 2018 18:29:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726949AbeHBUWC (ORCPT ); Thu, 2 Aug 2018 16:22:02 -0400 Received: from esa2.hgst.iphmx.com ([68.232.143.124]:12083 "EHLO esa2.hgst.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729034AbeHBUWC (ORCPT ); Thu, 2 Aug 2018 16:22:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=wdc.com; i=@wdc.com; q=dns/txt; s=dkim.wdc.com; t=1533234627; x=1564770627; h=from:to:cc:subject:date:message-id:in-reply-to: references; bh=ol9/YuKy+DAqcA0wEiK/3JzzqAl65j9XLnmRc+SKc58=; b=Z+oz8MJeDQkdPpKtl2GP+KpTKlUsAkbBjB7GPsLbJGCm9CdrpZiwXoyb 6nrfh/tmpYmLkjAwTX2jmPcxJPVGoDwyKgSnqLHeq2oHqhiDUXg83PSRl Yxpfa6PQS3bPWoPuMc9Hth7okbTnFgdvlnXYfGdpSkXQ8xw1cik43FXTT 1kZEDc6GLMtfo+EgWrhYF3Drqumwo3XJSipAgQ+7IL2lxSz1BfYQIrJHt iclR7Ut7QL+nKItUztQBWFobHjUIfb9rnmOmvBdcDfHWCJPwjJuS2+cfw SwEBANB7mrrtPJ35lke14Eflf5ZRxT4G+7Pl5sIIFBAfPKtKBP15ME2T+ g==; X-IronPort-AV: E=Sophos;i="5.51,436,1526313600"; d="scan'208";a="183378934" Received: from uls-op-cesaip01.wdc.com (HELO uls-op-cesaep01.wdc.com) ([199.255.45.14]) by ob1.hgst.iphmx.com with ESMTP; 03 Aug 2018 02:30:27 +0800 Received: from uls-op-cesaip01.wdc.com ([10.248.3.36]) by uls-op-cesaep01.wdc.com with ESMTP; 02 Aug 2018 11:18:08 -0700 Received: from thinkpad-bart.sdcorp.global.sandisk.com ([10.111.67.248]) by uls-op-cesaip01.wdc.com with ESMTP; 02 Aug 2018 11:29:45 -0700 From: Bart Van Assche To: Jens Axboe Cc: linux-block@vger.kernel.org, Christoph Hellwig , Bart Van Assche , Tejun Heo , Jianchao Wang , Ming Lei , Alan Stern , Johannes Thumshirn Subject: [PATCH v3 4/9] percpu-refcount: Introduce percpu_ref_read() Date: Thu, 2 Aug 2018 11:29:39 -0700 Message-Id: <20180802182944.14442-5-bart.vanassche@wdc.com> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20180802182944.14442-1-bart.vanassche@wdc.com> References: <20180802182944.14442-1-bart.vanassche@wdc.com> Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Introduce a function that allows to read the value of a per-cpu counter. This function will be used in the next patch to check whether a per-cpu counter in atomic mode has the value one. Signed-off-by: Bart Van Assche Cc: Tejun Heo Cc: Christoph Hellwig Cc: Jianchao Wang Cc: Ming Lei Cc: Alan Stern Cc: Johannes Thumshirn --- include/linux/percpu-refcount.h | 2 ++ lib/percpu-refcount.c | 29 +++++++++++++++++++++++++++++ 2 files changed, 31 insertions(+) diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h index 009cdf3d65b6..5707289ba828 100644 --- a/include/linux/percpu-refcount.h +++ b/include/linux/percpu-refcount.h @@ -331,4 +331,6 @@ static inline bool percpu_ref_is_zero(struct percpu_ref *ref) return !atomic_long_read(&ref->count); } +unsigned long percpu_ref_read(struct percpu_ref *ref); + #endif diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c index 9f96fa7bc000..c0b9fc8efa6b 100644 --- a/lib/percpu-refcount.c +++ b/lib/percpu-refcount.c @@ -369,3 +369,32 @@ void percpu_ref_reinit(struct percpu_ref *ref) spin_unlock_irqrestore(&percpu_ref_switch_lock, flags); } EXPORT_SYMBOL_GPL(percpu_ref_reinit); + +/** + * percpu_ref_read - read a percpu refcount + * @ref: percpu_ref to test + * + * This function is safe to call as long as @ref is between init and exit. It + * is the responsibility of the caller to handle changes of @ref concurrently + * with this function. If this function is called while @ref is in per-cpu + * mode the returned value may be incorrect if e.g. percpu_ref_get() is called + * from one CPU and percpu_ref_put() is called from another CPU. + */ +unsigned long percpu_ref_read(struct percpu_ref *ref) +{ + unsigned long __percpu *percpu_count; + unsigned long sum = 0; + int cpu; + + rcu_read_lock_sched(); + if (__ref_is_percpu(ref, &percpu_count)) { + for_each_possible_cpu(cpu) + sum += *per_cpu_ptr(percpu_count, cpu); + } + rcu_read_unlock_sched(); + sum += atomic_long_read(&ref->count); + sum &= ~PERCPU_COUNT_BIAS; + + return sum; +} +EXPORT_SYMBOL_GPL(percpu_ref_read);