From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 BA99B37E5C2 for ; Tue, 1 Sep 2026 05:24:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788240294; cv=none; b=lRSPRfcjiC7UjthRLR251drW9uoc5yRU1BCLVOa1CHmng99Qp4hBs01OFEdvdbEcxuXg7McYX7ST7JtuKEe/2oH1bKr8vbbboXnYZdnFLNEFGTGO15SIasD//FNmJcdj4KoA7Z78zC1sUEzS/67zNiqVwNDhJ0EaQE+ZGJr5qpg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788240294; c=relaxed/simple; bh=AjFpDQH04QGhhEU4DYYHqdOqekbBChrM43hX314Hnv4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=SLSFT3NObsL3igZGB3/ROHc4VLhxNihOe6+YzT/PpjLcg3c52FleLPXUHotIxy884A0G3aLyW3sE8dkIkY0bV9D2zzHniz9539I9mb6b9sJ9juYiF7PVDL1a22HM8InEXLTqesml7G/PIhe67QzMy1hr31wDq//DU5lKctEnUp0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AVNVB2if; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="AVNVB2if" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 423331F000E9; Tue, 1 Sep 2026 05:24:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788240293; bh=N1Qef8p6H5tPefGA87iHYtftZppHaVJg2EVht5kxbPk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=AVNVB2ifmTwEqHfxZz+A3FX3OjufZNgx4qnm5CKl3LJj/JDqBUFMnmRW62+uzT2u+ cQgDn9423OLOqmba2S2XCU4UmGZQm6sCKNiqsKt/NVkz7bFc1etADNduhmi4UqtadX DSyOBIMPNOi61FE9pvFtORqwPiylm+HAJlQC+KeOSGr+sWddKjjrnlKaXkafE5vC1F kmftWra2Wc1RAGgAk2+QvZKKeW8YPvgbB6YRdDTCzXYBb3j5FAstlgT2zzIGpec7NV cEpG76KqlqipgNE01eHcwUStt1YbnrVe2ehO27vvojtMTKdnxn9Lk2IcRNEkJQgWxP OwejYHO4DKp1w== From: SJ Park To: sashiko-bot@kernel.org Cc: SJ Park , damon@lists.linux.dev Subject: Re: [PATCH 13/17] mm/damon/sysfs: pass preps to DAMON core Date: Mon, 31 Aug 2026 22:24:44 -0700 Message-ID: <20260901052446.4122-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260901045314.9C8631F000E9@smtp.kernel.org> References: Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Tue, 01 Sep 2026 04:53:14 +0000 sashiko-bot@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: > - [Low] Data race on `sys_prep->action` due to lockless read and write > -- > > commit 09b46cd761363fb28603bd1d27adb637a6c16a7d > Author: SJ Park > > mm/damon/sysfs: pass preps to DAMON core > > DAMON sysfs interface provides the files for setting DAMON probe preps. > But the underlying code is not really passing the user-set values to > DAMON core. Pass those. > > > diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c > > index c0130843223d7..d02f5f8ceae5b 100644 > > --- a/mm/damon/sysfs.c > > +++ b/mm/damon/sysfs.c > > @@ -2176,6 +2176,23 @@ static int damon_sysfs_set_attrs(struct damon_ctx *ctx, > > return damon_set_attrs(ctx, &attrs); > > } > > > > +static int damon_sysfs_set_preps(struct damon_probe *probe, > > + struct damon_sysfs_preps *sys_preps) > > +{ > > + int i; > > + > > + for (i = 0; i < sys_preps->nr; i++) { > > + struct damon_sysfs_prep *sys_prep = sys_preps->preps_arr[i]; > > + struct damon_prep *prep; > > + > > + prep = damon_new_prep(sys_prep->action); > > [Severity: Low] > Could this result in a data race on sys_prep->action? > > During DAMON context building, this locklessly reads the action enum while a > concurrent root user could be writing to the /sys/.../prep_action attribute. > > A concurrent write to prep_action could happen while another process issues a > commit command to the state file, which runs damon_sysfs_commit_input > asynchronously on the kdamond thread without holding damon_sysfs_lock. > > Would it be better to use READ_ONCE() here, along with a corresponding > WRITE_ONCE() on the writer side, to adhere to the Linux Kernel Memory Model > guidelines and avoid potential KCSAN warnings? Good catch. A few similar call paths protect stores with damon_sysfs_lock. I will protect prep->action writing with the lock. Because the context build is done while holding the lock, it should avoid the race, like below. ''' --- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -827,7 +827,10 @@ static ssize_t prep_action_store(struct kobject *kobj, action_name = &damon_sysfs_prep_action_names[i]; if (sysfs_streq(buf, action_name->name)) { + if (!mutex_trylock(&damon_sysfs_lock)) + return -EBUSY; prep->action = action_name->action; + mutex_unlock(&damon_sysfs_lock); ret = count; break; } ''' > > > + if (!prep) > > + return -ENOMEM; > > + damon_add_prep(probe, prep); > > + } > > + return 0; > > +} > > + > > [ ... ] > > -- > Sashiko AI review ยท https://sashiko.dev/#/patchset/20260901043417.2165-1-sj@kernel.org?part=13 Thanks, SJ