From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 2B686168BD; Wed, 3 Apr 2024 14:16:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712153797; cv=none; b=b+qXL1xQOmkQ70InSLwFD7P9RC7eUbRIeyFDtALG73nlIFcNjcJkE4vcnHRuFbvHc9gD05NDA3V0jmcUH6ivAWIWhgGfN3FtefdcFKtV9RletHAmZlQAR12/7U++0xM6JFrBVT5TplAkBFf1bZvgVaGGIDrt6tAOLODUHbRJPxY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712153797; c=relaxed/simple; bh=QVNG9klf635AF8QatLYX+kN3E3QTHjJIn6uyjkTeFnE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ejD7l6yCm9JT7jRyd/1XR1U75CoqXk3ivyHSS5JLodVbw1aniHEm1sv8dSpnh8s0UKyMPrUmr3tCXP6KMDa0SsQpfTdlgoOcMLIykIETWKixYtrOk9Gt1DPWO26LMnfEoPIqr1swJxQ9tu18rD6c+tzV4G/Zv+Me6VFpHESKd6k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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> Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240403125109.2054881-3-dawei.li@shingroup.cn> 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 >