From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794092653; b=YdBJbFongPvdXEqem4MpbDVWC6Z0GivDJcSmvqKy6j5qBe6U+6Iv0P/M8sCRtypiOuLZ mjaoTutoVnJJGWYjk+6O70p5V8OE2sV/PIrwXtBc2vNqV9d5QFsNVInylxwK/xia56gjF pAb5Wde4XxIEYwOCkE6w/7z7oMlfO6HVfXiHL/q0jLDYh8a16rMAJ9fNp4JYxOHSfCE3g rxbrAxomjzaZOsrBZ4aMFhiupjNnVEbpYJ2mQtSJf24nJYdRNgh9N45j2Q63Qd4+0wemA 7OpxzZxbMYDUfrxfKiMmxtH5o8v5LIOkLyMrVCDaRDXUILjSeK44OtuBZgiK50iDe4A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794092653; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Type: Content-Transfer-Encoding; bh=UKOheFdZkwgZbCvgxDw/KrEQq5eknMllMtNA2ffj/I0=; b=UoUTKtieHzfRClawbVeMcdtTOFxk3o+jKi/ych53m0ufwvDZBhNUsDL74bGA19r0Z9NW OaTkxln5xzQH9W+aYwaQkrtUGsWTznKe41ZaqlG/mNCuccLSZD5tc52ts23NayYfNf+fy ZWnp4rYeaen0tJ89lSKKAMVZWEObBb+YZKp9COwsy1prQU+wRm68HjEw5hZmxzcEbNUwa t17TcZgynwcXfdKqedL+YoXKp9VyQnIzoTuE+MgXdpnvyGZ4eDkaTfg40R81IidIhwPsi 2IdQNAY1IqRgCQCvP08ysNCYJUuBRji3ocd3947dbOdMGjlIXzvt67wFZtsnJekQ1vA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=lqXFDyDV; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 36F58606A32C for ; Sat, 7 Nov 2026 23:04:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=lqXFDyDV Received: by smtp.kernel.org (Postfix) with ESMTPSA id A8BDE1F0089F; Sat, 7 Nov 2026 23:04:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794092652; bh=UKOheFdZkwgZbCvgxDw/KrEQq5eknMllMtNA2ffj/I0=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=lqXFDyDV9otA+OWWxyegWyB2sC0/phLyMCIu69a/z/18CcyyzQHkRiRwLNAU4uT9x UHmK7u7+y6j1MNI/A2UQAN4HdnMDn8tCIO3z2TvFbK4XPsMn0aF+kZOlGS810H+alZ oMI2C8UdG5ZSu1ET+OgQwZvDc8zZz+pZh9C9xwePCd/4hCJhqLtsmEOOCMVd0V4o9Y x2lA6i6eCj0auShuv8ePOU+93xYhtm50RIIRHSDdX4M+7f2YjPok+TRGUXUtIFfcve MIX548aVJMghxoE/I2gJz4+uUST8UZSgeeA0+laDNPVOk+Ceoe/W8N3NMlefqlC8jO 263bKfaqOVWqg== From: SJ Park To: sashiko-bot@kernel.org Cc: SJ Park , "Andrew Morton" , damon@lists.linux.dev, linux-mm@kvack.org Subject: Re: [RFC PATCH 6.1.y 2/2] mm/damon/core: remove unreachable damos charge_{target,addr}_from Date: Sat, 7 Nov 2026 15:04:04 -0800 Message-ID: <20261107230406.340832-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: References: X-Mailing-List: damon@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Sat, 07 Nov 2026 23:02:33 +0000 sashiko-bot@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found 1 potential > issue to consider: > - [Medium] mm/damon/core: stale charge_target_from ABA reuse when scheme > is inactive > -- > > commit 853b3e89da132f2ce03750bcf6dfc1f62a70d261 > Author: SJ Park > > mm/damon/core: remove unreachable damos charge_{target,addr}_from > > This commit adds damos_fix_stale_charge_pointers() to clear > quota->charge_target_from and quota->charge_addr_from when the referenced > target has been removed or no longer has any regions. > > Link: https://lore.kernel.org/20261020023958.108276-1-sj@kernel.org > > > diff --git a/mm/damon/core.c b/mm/damon/core.c > > index 9206737d05ae7..01f93146b92fe 100644 > > --- a/mm/damon/core.c > > +++ b/mm/damon/core.c > > @@ -860,6 +860,26 @@ static void damos_set_effective_quota(struct damos_quota *quota) > > quota->esz = esz; > > } > > > > +static void damos_fix_stale_charge_pointers(struct damon_ctx *c, > > + struct damos *s) > > +{ > > + struct damos_quota *quota; > > + struct damon_target *t; > > + > > + quota = &s->quota; > > + if (!quota->charge_target_from) > > + return; > > + damon_for_each_target(t, c) { > > + if (t == quota->charge_target_from) { > > + if (damon_nr_regions(t) > 0) > > + return; > > + break; > > + } > > + } > > + quota->charge_target_from = NULL; > > + quota->charge_addr_from = 0; > > +} > > + > > static void kdamond_apply_schemes(struct damon_ctx *c) > > { > > struct damon_target *t; > > @@ -890,6 +910,8 @@ static void kdamond_apply_schemes(struct damon_ctx *c) > > damos_set_effective_quota(quota); > > } > > > > + damos_fix_stale_charge_pointers(c, s); > > + > > if (!c->ops.get_scheme_score) > > continue; > > > > [Severity: Medium] > Can quota->charge_target_from match a newly allocated target due to slab > address reuse if the old target was freed while the scheme was inactive? > > kdamond_apply_schemes() skips inactive schemes at the !s->wmarks.activated > check before reaching damos_fix_stale_charge_pointers(), and > damon_sysfs_set_targets() frees removed targets via damon_destroy_target() > without clearing charge_target_from. If an online commit removes the > target stored in charge_target_from while the scheme is deactivated by > watermarks and a later commit allocates a new target at the same address, > damos_fix_stale_charge_pointers() will see t == quota->charge_target_from > with regions present and leave the stale charge_target_from and > charge_addr_from in place. When the scheme reactivates, > damon_do_apply_schemes() will skip targets before the new target and > regions up to the old charge_addr_from. Good finding but no real issue. Occasionally starting quota charging from an unexpected target is no real issue for DAMOS in my opinion. So, no blocker. > > -- > Sashiko AI review ยท https://sashiko.dev/#/patchset/20261107224800.340250-1-sj@kernel.org?part=2 > Thanks, SJ