From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1EBAA219303; Thu, 23 Apr 2026 01:22:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776907321; cv=none; b=cJTLsfmyr+2kt2C8m6kSSgdE/228E1pOIMagm828GYYfELdWLhu2YADmDsshUfr4JFuEW5mOWrPWa3scJRVUmp5o2GG8mCfjXChRa52TsdMAiXNuJnpB3pPIUQJ6NAqqFelhoYUQNK+blsY0A60q+2AOylvqfIK+Twi3vFbnetQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776907321; c=relaxed/simple; bh=EnCedkb3XVDzVcvu88jL0boWfgFwhTeskY/8A0Dc0t8=; h=From:Subject:To:Cc:In-Reply-To:References:Content-Type:Date: Message-Id; b=MjYT/w40f7eE2MKit/rJgL/TboFVB5yg23mV6q4y/iCVvKp4nqXwG+EKUP2GVQ6HZ44zS98zaW9lkvLVzDiWJ7FgtUPobuHmpbWF+BcPqifFMTYdL3Egr+nev0NYWT4leNtbyOFeZWJ8ZvesXNwuy+oTTFZwXO/BXLHlPmLUWjs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rArPaMxG; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="rArPaMxG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 955F7C2BCB2; Thu, 23 Apr 2026 01:22:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776907320; bh=EnCedkb3XVDzVcvu88jL0boWfgFwhTeskY/8A0Dc0t8=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date:From; b=rArPaMxGAc2U4eTAMO3jWoRf4LeT2bd9MnEBOITAcLo8eq6m1tpFiG0C5yjQ+EaNi 8cjy4a08fEu3Ps9FPUXXmlNUsC34i+MK0+JiP+GXHAoxdeHKSwUslDaf81YOwwjDKH XwGYXOo9smbyQ1SQpXJIk33tREaDGK3PJfgVc76i4g/l9fNG7b8ZjAmhJOXgZ6pswb E5P8nXF87R0gTFKQSxsNejOh6tGPPIGtUr6d6dlwcWa5iUCC74SlqKhLYIEgvMQ83F /Qci6t4CL4P+V+UlxzGSJ0c1BevsfkvX9OZEkvMrUQRjiL++0KjlR8xH4So2+Km6hK +3Yx+PUZMM9Cg== From: sashiko-bot@kernel.org Subject: Re: [RFC PATCH v3 1/4] mm/damon/core: add code borrowed from report-based monitoring work Reply-To: sashiko@lists.linux.dev To: "Akinobu Mita" Cc: damon@lists.linux.dev, linux-perf-users@vger.kernel.org In-Reply-To: <20260423004211.7037-2-akinobu.mita@gmail.com> References: <20260423004211.7037-2-akinobu.mita@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Thu, 23 Apr 2026 01:21:59 +0000 Message-Id: <20260423012200.955F7C2BCB2@smtp.kernel.org> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Sashiko AI review found 2 potential issue(s): - [Medium] Stack bloat / stack overflow risk from `cpumask_t` allocation on= the stack. - [Medium] Data race and potential torn reads from lockless assignment of `= cpumask_t`. -- commit 9c32a9c6100e762865883bc9bf4b2272ccb6dedb Author: Akinobu Mita mm/damon/core: add code borrowed from report-based monitoring work =20 This commit borrows code from the report-based monitoring infrastructure to support perf event-based monitoring. It brings in struct damon_access_report, an access_reported field in damon_region, and the sample/primitives sysfs directory structure. =20 Link: https://lore.kernel.org/linux-mm/20251208062943.68824-6-sj@kernel.org= /T/ > diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c > index eefa959aa30ae..c19556f2af3bb 100644 > --- a/mm/damon/sysfs.c > +++ b/mm/damon/sysfs.c [ ... ] > +static ssize_t cpumask_store(struct kobject *kobj, struct kobj_attribute= *attr, > + const char *buf, size_t count) > +{ > + struct damon_sysfs_sample_filter *filter =3D container_of(kobj, > + struct damon_sysfs_sample_filter, kobj); > + cpumask_t cpumask; Is it safe to allocate cpumask_t on the stack here? The size of cpumask_t scales with CONFIG_NR_CPUS. On systems with a large number of CPUs, this could consume a significant amount of the kernel stack and potentially risk a stack overflow. Should this use alloc_cpumask_var() instead to dynamically allocate the temporary mask? > + int err =3D cpulist_parse(buf, &cpumask); > + > + if (err) > + return err; > + filter->cpumask =3D cpumask; Can this lockless assignment cause a data race or torn reads? Because cpumask_t can be larger than a single word, this assignment may compile into a non-atomic multi-word copy like memcpy(). If a concurrent sysfs read in cpumask_show() or a DAMON commit operation accesses filter->cpumask while this copy is ongoing, could it read a partially updated, torn mask? Should this be protected by explicit synchronization, such as damon_sysfs_lock? > + return count; > +} --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260423004211.7037= -1-akinobu.mita@gmail.com?part=3D1