From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id BD543CD1288 for ; Wed, 3 Apr 2024 14:16:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=vkcL9YIrAnWwonR1jFcwoKNjUzHC0EZPWtNNhZ4L5zY=; b=ed0L8SPD6wK7Si aMFRcCdvuVizCkd8U1jRFkYRMVqpA3RnFwK66NQNu7FcxY1UoBdcwUzaa9i9ZIjwuRL59MEW+GSml 2V1OGif68Mu/r08NOrZouuP2hJuLqneY7m2UxddCsWqVdxE4XcxO19ZNEIUIzmuhpfePfuPKfYLN1 q2uM1NCbZpswAMpNj3JesxJrDmjOktq2RcxcGqeKP4EnVjleYMADBOujfQYZtFOyIB+8U08HQD8aK 46c+v7yRetVQ8Wv2FIKk8z/m5ke2Aqt+Eony20HSfZywZicOEj3SlLep2tY4l8sSgXRh+n6riFHwy LmuU+QuAnVNIxLpUQuxQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1rs1Pu-0000000GPOk-0UIa; Wed, 03 Apr 2024 14:16:42 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1rs1Pr-0000000GPNm-0ChP for linux-arm-kernel@lists.infradead.org; Wed, 03 Apr 2024 14:16:40 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6EE391007; Wed, 3 Apr 2024 07:17:05 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.16.212]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2070E3F7B4; Wed, 3 Apr 2024 07:16:31 -0700 (PDT) Date: Wed, 3 Apr 2024 15:16:24 +0100 From: Mark Rutland To: Dawei Li Cc: will@kernel.org, yury.norov@gmail.com, linux@rasmusvillemoes.dk, xueshuai@linux.alibaba.com, renyu.zj@linux.alibaba.com, yangyicong@hisilicon.com, jonathan.cameron@huawei.com, andersson@kernel.org, konrad.dybcio@linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org Subject: Re: [PATCH v2 02/10] perf/alibaba_uncore_drw: Avoid placing cpumask var on stack Message-ID: References: <20240403125109.2054881-1-dawei.li@shingroup.cn> <20240403125109.2054881-3-dawei.li@shingroup.cn> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20240403125109.2054881-3-dawei.li@shingroup.cn> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240403_071639_200875_1D073524 X-CRM114-Status: GOOD ( 24.58 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Apr 03, 2024 at 08:51:01PM +0800, Dawei Li wrote: > For CONFIG_CPUMASK_OFFSTACK=y kernel, explicit allocation of cpumask > variable on stack is not recommended since it can cause potential stack > overflow. > > Instead, kernel code should always use *cpumask_var API(s) to allocate > cpumask var in config-neutral way, leaving allocation strategy to > CONFIG_CPUMASK_OFFSTACK. > > But dynamic allocation in cpuhp's teardown callback is somewhat problematic > for if allocation fails(which is unlikely but still possible): > - If -ENOMEM is returned to caller, kernel crashes for non-bringup > teardown; > - If callback pretends nothing happened and returns 0 to caller, it may > trap system into an in-consisitent/compromised state; > > Use newly-introduced cpumask_any_and_but() to address all issues above. > It eliminates usage of temporary cpumask var in generic way, no matter how > the cpumask var is allocated. > > Suggested-by: Mark Rutland > Signed-off-by: Dawei Li I don't think we need to explain all the pitfalls of the approach we haven't taken. Could we please simplify this down to: Could we please get rid of the bit that says we should "always use the *cpumask_var API(s)", and simplify the commit message down to: | perf/alibaba_uncore_drw: Avoid placing cpumask on the stack | | In general it's preferable to avoid placing cpumasks on the stack, as | for large values of NR_CPUS these can consume significant amounts of | stack space and make stack overflows more likely. | | Use cpumask_any_and_but() to avoid the need for a temporary cpumask on | the stack. The logic looks good to me, so with that commit message: Reviewed-by: Mark Rutland Mark. > --- > drivers/perf/alibaba_uncore_drw_pmu.c | 10 +++------- > 1 file changed, 3 insertions(+), 7 deletions(-) > > diff --git a/drivers/perf/alibaba_uncore_drw_pmu.c b/drivers/perf/alibaba_uncore_drw_pmu.c > index a9277dcf90ce..d4d14b65c4a5 100644 > --- a/drivers/perf/alibaba_uncore_drw_pmu.c > +++ b/drivers/perf/alibaba_uncore_drw_pmu.c > @@ -746,18 +746,14 @@ static int ali_drw_pmu_offline_cpu(unsigned int cpu, struct hlist_node *node) > struct ali_drw_pmu_irq *irq; > struct ali_drw_pmu *drw_pmu; > unsigned int target; > - int ret; > - cpumask_t node_online_cpus; > > irq = hlist_entry_safe(node, struct ali_drw_pmu_irq, node); > if (cpu != irq->cpu) > return 0; > > - ret = cpumask_and(&node_online_cpus, > - cpumask_of_node(cpu_to_node(cpu)), cpu_online_mask); > - if (ret) > - target = cpumask_any_but(&node_online_cpus, cpu); > - else > + target = cpumask_any_and_but(cpumask_of_node(cpu_to_node(cpu)), > + cpu_online_mask, cpu); > + if (target >= nr_cpu_ids) > target = cpumask_any_but(cpu_online_mask, cpu); > > if (target >= nr_cpu_ids) > -- > 2.27.0 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel