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 AE4427172B; Wed, 3 Apr 2024 14:23:29 +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=1712154212; cv=none; b=l4wflsM7zIZPuizeNYNr8ReDy1Mtci3c4fXncyx7W/A/kkj9J0RUSiQL6VVrkJ4SVcpH2ddGReEONLU0ap/7GcOyTQAgWn9ocWMHfHicSLRzIRNe19SmFw2gbcqRHTSJg5p5yVFbamSUCknr//15E5qhpJ1AfqHWwVSjet39Frk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712154212; c=relaxed/simple; bh=SFg47yxUbctV3PGgM85vXl4SA4wjFf1zK2RoTvmRxXc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=F12na4f+sJEGmhTTodA9Y/yBIW4fYaDGxSX+2J7+IXvod24zGNdw1Od7BhERbo89eOaF7Na0tNk60TL3xKBrQAcRgE4RjSoeSrJrltzFghnLGOtWFU9pnNvwPCkx7ywZF9JU9y7F7p9nqn35O95SXkqedQzU8CkXqqJm5mHRHqc= 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 2A7ED1007; Wed, 3 Apr 2024 07:24:00 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.16.212]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CE21D3F7B4; Wed, 3 Apr 2024 07:23:26 -0700 (PDT) Date: Wed, 3 Apr 2024 15:23:24 +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 03/10] perf/arm-cmn: Avoid placing cpumask var on stack Message-ID: References: <20240403125109.2054881-1-dawei.li@shingroup.cn> <20240403125109.2054881-4-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: <20240403125109.2054881-4-dawei.li@shingroup.cn> On Wed, Apr 03, 2024 at 08:51:02PM +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-cmn.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c > index 7ef9c7e4836b..6bfb0c4a1287 100644 > --- a/drivers/perf/arm-cmn.c > +++ b/drivers/perf/arm-cmn.c > @@ -1950,20 +1950,20 @@ static int arm_cmn_pmu_offline_cpu(unsigned int cpu, struct hlist_node *cpuhp_no > struct arm_cmn *cmn; > unsigned int target; > int node; > - cpumask_t mask; > > cmn = hlist_entry_safe(cpuhp_node, struct arm_cmn, cpuhp_node); > if (cpu != cmn->cpu) > return 0; > > node = dev_to_node(cmn->dev); > - if (cpumask_and(&mask, cpumask_of_node(node), cpu_online_mask) && > - cpumask_andnot(&mask, &mask, cpumask_of(cpu))) > - target = cpumask_any(&mask); > - else > + > + target = cpumask_any_and_but(cpumask_of_node(node), cpu_online_mask, cpu); > + if (target >= nr_cpu_ids) > target = cpumask_any_but(cpu_online_mask, cpu); > + > if (target < nr_cpu_ids) > arm_cmn_migrate(cmn, target); > + > return 0; > } > > -- > 2.27.0 >