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 1B1EB431E5F; Mon, 13 Jul 2026 13:58:48 +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=1783951129; cv=none; b=KhyznhK7UxDEch8eISFZEjFqGwGRxNRk1qKntwzco13w92FBTYCLvj+kOTgQBH3VUnPNmJSfbMKguFKLzgGhE8Uv8NTJdR7O7mfBO4i2DVX0RW3g1UXnsBbJmYkAJzudSJJ/3SqEpvuWqGRAEKoK/tDOTs2266/lCbuHYLiDN1o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783951129; c=relaxed/simple; bh=nt1m4yOHpUkfhmuPI5sfQNBML1ejUt2LDcM7VHyWuzk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=WISEKQAFmxbI1oJiX4jTDQ1fwLkmWcZOw1uD0PiaLut1dMZWRjCdif4RvXC2IEpztZcEVKpcdCwHtqCEQwO2alp2JKyyU1nXIr6Vqqlf5Yc6PdOAiUHUNIP2nkPu0s8K5ZxdbifU5CuLbGozMe9uOHyQfiZwu7URIVw+9yBeMqQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=euZHtD/a; 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="euZHtD/a" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A566E1F00AC4; Mon, 13 Jul 2026 13:58:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783951127; bh=hhmDCI+ot7IL3VsT3pLzYBJmbk4njLZd345nGTc/fNs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=euZHtD/aDvIZBDQjpyKLp0lEEVw3YHagyScpG6RM09WNsMcQ/ypT/C9GcVouODud+ 8p5nPr2a84cQB1FrIzkdjnfj1SNgF6FfBFCRN/6/DUUCJcZqg06eeKx0pgLwhVFsAr dXkjFMa3AYDXtLwtk0Ryh6Dvfw1KtBQcIzXUiEedRoAInwPVDYv+U+bsyRJUbX2rzc t4aIw4thGprKvXHV/Wz+NL9338m7P/vHz7Q9nFG2eVUctNjPMVqjMkKvAbsp8aPn1a 93oyYPQkCN2QrwjSBR6/heoQ+mS1s0LprpOUeKW4L/tqjCvl731WSr0tEXZHCww9ju METmJcFrUwk5g== From: SJ Park To: Cc: SJ Park , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH v1.2 5/5] mm/damon/sysfs: read ops_id only once Date: Mon, 13 Jul 2026 06:58:36 -0700 Message-ID: <20260713135838.32730-6-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260713135838.32730-1-sj@kernel.org> References: <20260713135838.32730-1-sj@kernel.org> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit damon_sysfs_apply_inputs() reads ops_id twice. It could race with ops_id_store(). As a result, the min_region_sz could wrongly be set up. Read it once. The user impact is trivial. Sane users ain't update the parameter in parallel. Even if it happens, only monitoring itself runs differently than expected. No critical consequences like kernel panic or memory corruption happen. The issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260703172417.95426-1-sj@kernel.org Signed-off-by: SJ Park --- mm/damon/sysfs.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c index b5fe036f78015..60a1a9e4ada34 100644 --- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -2094,14 +2094,16 @@ static inline bool damon_sysfs_kdamond_running( static int damon_sysfs_apply_inputs(struct damon_ctx *ctx, struct damon_sysfs_context *sys_ctx) { + enum damon_ops_id ops_id; int err; - err = damon_select_ops(ctx, sys_ctx->ops_id); + ops_id = READ_ONCE(sys_ctx->ops_id); + err = damon_select_ops(ctx, ops_id); if (err) return err; ctx->addr_unit = sys_ctx->addr_unit; /* addr_unit is respected by only DAMON_OPS_PADDR */ - if (sys_ctx->ops_id == DAMON_OPS_PADDR) + if (ops_id == DAMON_OPS_PADDR) ctx->min_region_sz = max( DAMON_MIN_REGION_SZ / sys_ctx->addr_unit, 1); ctx->pause = sys_ctx->pause; -- 2.47.3