From patchwork Wed Aug 16 15:12:03 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marc Zyngier X-Patchwork-Id: 9903947 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id B3FFA6038C for ; Wed, 16 Aug 2017 15:12:54 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A0EB5288A3 for ; Wed, 16 Aug 2017 15:12:54 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 91B2228A19; Wed, 16 Aug 2017 15:12:54 +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=-2.6 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,RCVD_IN_DNSWL_LOW autolearn=ham version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [65.50.211.133]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 08EE2288A3 for ; Wed, 16 Aug 2017 15:12:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date: Message-ID:From:References:To:Subject:Reply-To:Cc:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=z366Eq6cyKDTdDpEAoE4HjlzV2V2QwyXHcaDIjq0Vg4=; b=kDAcr0dskbJ1WcawybIs0JIT8M leGFx5M82NYqKaRlkYsH2XunrSNFc88UU0SsZESoCjU9hDJZ4Z2MzZivPsSUDpHdaZcU273STnHoH Qipbh9jElFshmMpz5w1EmKKihAe3s9SN96RELEABb/ihQcwtrj+n5y6Bkn1jPBDrPq82MUq3deyXC lROHBZ7v0s5kE0DfPjqw7pCa1O4fg74Hhi6uhPkxZcKGqbV/MKoXGJlwY6rq7R7rR0WNLjsqbP/97 a5HTFEdcxNQd9JxwqvjtCNt3UleSVFSpRTixjNFEyjTFt1HasTSON3jwsE6yJrundbbxIVQw6ycS3 9KAwDWKw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.87 #1 (Red Hat Linux)) id 1dhzzq-00075k-QZ; Wed, 16 Aug 2017 15:12:38 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.87 #1 (Red Hat Linux)) id 1dhzzd-0006lA-FC for linux-arm-kernel@lists.infradead.org; Wed, 16 Aug 2017 15:12:30 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 47A022B; Wed, 16 Aug 2017 08:12:05 -0700 (PDT) Received: from [10.1.207.16] (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C25403F577; Wed, 16 Aug 2017 08:12:04 -0700 (PDT) Subject: Re: [PATCH] irqchip/gic-v3-its: handle queue wrapping in its_wait_for_range_completion() To: Yang Yingliang , linux-arm-kernel@lists.infradead.org References: <1502888682-12148-1-git-send-email-yangyingliang@huawei.com> From: Marc Zyngier Organization: ARM Ltd Message-ID: Date: Wed, 16 Aug 2017 16:12:03 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <1502888682-12148-1-git-send-email-yangyingliang@huawei.com> Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20170816_081226_207747_3B604980 X-CRM114-Status: GOOD ( 16.75 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP Hi Yang, On 16/08/17 14:04, Yang Yingliang wrote: > If the to_idx wrap to 0, (rd_idx >= to_idx) will be true, > but the command is not completed. > > When to_idx is smaller than from_idx, it means the queue > is wrapped. For handling this case, add ITS_CMD_QUEUE_SZ > to to_idx and rd_idx to. > > Signed-off-by: Yang Yingliang > --- > drivers/irqchip/irq-gic-v3-its.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c > index 6893287..8e47515 100644 > --- a/drivers/irqchip/irq-gic-v3-its.c > +++ b/drivers/irqchip/irq-gic-v3-its.c > @@ -446,13 +446,18 @@ static void its_wait_for_range_completion(struct its_node *its, > struct its_cmd_block *to) > { > u64 rd_idx, from_idx, to_idx; > + u32 wrap_offset = 0; > u32 count = 1000000; /* 1s! */ > > from_idx = its_cmd_ptr_to_offset(its, from); > to_idx = its_cmd_ptr_to_offset(its, to); > + if (to_idx < from_idx) { > + wrap_offset = ITS_CMD_QUEUE_SZ; > + to_idx += ITS_CMD_QUEUE_SZ; > + } > > while (1) { > - rd_idx = readl_relaxed(its->base + GITS_CREADR); > + rd_idx = readl_relaxed(its->base + GITS_CREADR) + wrap_offset; > if (rd_idx >= to_idx || rd_idx < from_idx) > break; > > I think you've spotted a real issue, but the way you solve it hurts my brain. I'd rather have something that makes the cases explicit. Does the following work for you? Secondary question: have you seen this breaking in practice? The worse case seems that we exit early, and potentially fail to detect a hung ITS. But that should never happen, right? Thanks, M. diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c index 22e228500357..374977681384 100644 --- a/drivers/irqchip/irq-gic-v3-its.c +++ b/drivers/irqchip/irq-gic-v3-its.c @@ -453,7 +453,13 @@ static void its_wait_for_range_completion(struct its_node *its, while (1) { rd_idx = readl_relaxed(its->base + GITS_CREADR); - if (rd_idx >= to_idx || rd_idx < from_idx) + + /* Direct case */ + if (from_idx < to_idx && rd_idx >= to_idx) + break; + + /* Wrapped case */ + if (from_idx >= to_idx && rd_idx >= to_idx && rd_idx < from_idx) break; count--;