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 062B4148FF5; Wed, 3 Apr 2024 14:21:15 +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=1712154077; cv=none; b=VDTQ6IQh2MMRrIIFcab86AXfEnXo/L2st2KdnkDiOxleAR3Y/LWNxBYLEw9640wYaeFyyVUuUAKaM1lbk5EFXmESTRZyU+1uL4CnebNwnN8VQKR3rti3tbpVUXQymDtKkziF/HSd7AtM8q8vcFmXEWnffv1AJkWigCNpyTDpj/E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712154077; c=relaxed/simple; bh=nqFwo/kHXwvxaX3Pir+qxJc7morMd5qBw4IR/1jIKSk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=GymRZjdYPtJv+vMdw4dOILRak3DPFq+QSh/xclZHabJDQUDX4hOSc6/bYEbUlnhw7z5+HUFFdZrwHvsnEtpdixMHpU4VZFvWsVYhJVN2Iq+Z+PFJQoPn077sejOfDSfBdCUvjg6q2uLZaX1KVvcV8A/0tIEMDa07l3OBYIG2iQU= 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 6C79E1007; Wed, 3 Apr 2024 07:21:46 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.16.212]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 226733F7B4; Wed, 3 Apr 2024 07:21:12 -0700 (PDT) Date: Wed, 3 Apr 2024 15:21:10 +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 04/10] perf/arm_cspmu: Avoid placing cpumask var on stack Message-ID: References: <20240403125109.2054881-1-dawei.li@shingroup.cn> <20240403125109.2054881-5-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: <20240403125109.2054881-5-dawei.li@shingroup.cn> On Wed, Apr 03, 2024 at 08:51:03PM +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 The logic looks good to me, but I'd like the commit message updated the same as per my comment on patch 2. With that commit message: Reviewed-by: Mark Rutland Mark. > --- > drivers/perf/arm_cspmu/arm_cspmu.c | 8 +++----- > 1 file changed, 3 insertions(+), 5 deletions(-) > > diff --git a/drivers/perf/arm_cspmu/arm_cspmu.c b/drivers/perf/arm_cspmu/arm_cspmu.c > index b9a252272f1e..fd1004251665 100644 > --- a/drivers/perf/arm_cspmu/arm_cspmu.c > +++ b/drivers/perf/arm_cspmu/arm_cspmu.c > @@ -1322,8 +1322,7 @@ static int arm_cspmu_cpu_online(unsigned int cpu, struct hlist_node *node) > > static int arm_cspmu_cpu_teardown(unsigned int cpu, struct hlist_node *node) > { > - int dst; > - struct cpumask online_supported; > + unsigned int dst; > > struct arm_cspmu *cspmu = > hlist_entry_safe(node, struct arm_cspmu, cpuhp_node); > @@ -1333,9 +1332,8 @@ static int arm_cspmu_cpu_teardown(unsigned int cpu, struct hlist_node *node) > return 0; > > /* Choose a new CPU to migrate ownership of the PMU to */ > - cpumask_and(&online_supported, &cspmu->associated_cpus, > - cpu_online_mask); > - dst = cpumask_any_but(&online_supported, cpu); > + dst = cpumask_any_and_but(&cspmu->associated_cpus, > + cpu_online_mask, cpu); > if (dst >= nr_cpu_ids) > return 0; > > -- > 2.27.0 >