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imf17.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=jIlYlZF+; spf=pass (imf17.hostedemail.com: domain of sj@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=sj@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1771105295; a=rsa-sha256; cv=none; b=UxIkJHcPT8fc2tNKahBM/amC4j/N5mojdBNW5Q3d5QmPUMleCZP5WPbhU4m8Vf+IHtzHBI cPVCRvLbZ5f7FveMXSmuFL26jrFEnlcOQR9Erwhjda+eL8N9XLw/E0e2ZdalIGRK9VtPTz 99cpuLlf19dsNio2XN5dqFxwigXPNps= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 4E773600BB; Sat, 14 Feb 2026 21:41:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D8B0DC16AAE; Sat, 14 Feb 2026 21:41:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771105294; bh=pjkwKmulTQMrj0f/NejRYLH42ooATAnuXxjLQOaFmfM=; h=From:To:Cc:Subject:Date:From; b=jIlYlZF+4PBNJ7bt04XHmqAWbG0k5pm94I/ik9/XFVg5T9UhMReiebz6qrbNCjikC 2VrBquWKBfpb9Wy9KM7Q24Sld5kulGZUULOwxzDwoxy6+d+1SiCPF5aIW21weTa2LV Yltx3HWvDYu+TI7i3NPhEJ/7SnQUmXsRT8BKjvs09BY7YI0svnh4dm6hHDZfKHNjJV j55Qq7pDtKVuS+wS+CSfxxQK7DA4NBt7rATEF6VVe08XrDbABHfMx8fT2UOjcLZo/8 3wpnmUzh09Bbba6wsoEuJaIFH2voQemC00BkqAvA2QjKoZBRPdY8CIXExtDgGwkAHj SioomFYV9E26Q== From: SeongJae Park To: Andrew Morton Cc: SeongJae Park , "# 6 . 18 . x" , Quanmin Yan , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH] mm/damon/core: disallow non-power of two min_region_sz Date: Sat, 14 Feb 2026 13:41:21 -0800 Message-ID: <20260214214124.87689-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Stat-Signature: 46hfmsnk6rooo3nroxhfmrxmc3krzk3t X-Rspam-User: X-Rspamd-Queue-Id: 0343A40006 X-HE-Tag: 1771105294-606326 X-HE-Meta: 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 5sIWR11l Fy/2o15CCkz5wNxKtdg83CRf+vj7fM9ga9lE2pOMyBsBwxdkb2PHNU0YM+CHFHjTtmVLSKLsNZpoBHADVcDpUnVQXr+dMQG4f3N309jTGwdfNijAkHCFR5+QgSm6xZalu9szyJyc2f2lm5SoQhlcb1k3dTi7Q11yH28QbrJSSOV1F7r8ZRdzxaxCw1lUxnsjSYn0hqjENHxvVA99q4bJF7f/UIbDeo0kOkKcrgdW0/SGiu6NPHCrjLtqCzhQMxdbHFh4qqwo6UmBD3dXBkZlU88Hrjg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: DAMON core uses min_region_sz parameter value as the DAMON region alignment. The alignment is made using ALIGN() and ALIGN_DOWN(), which support only the power of two alignments. But DAMON core API callers can set min_region_sz to an arbitrary number. Users can also set it indirectly, using addr_unit. When the alignment is not properly set, DAMON behavior becomes difficult to expect and understand, makes it effectively broken. It doesn't cause a kernel crash-like significant issue, though. Fix the issue by disallowing min_region_sz input that is not a power of two. Add the check to damon_commit_ctx(), as all DAMON API callers who set min_region_sz uses the function. This can be a sort of behavioral change, but it does not break users, for the following reasons. As the symptom is making DAMON effectively broken, it is not reasonable to believe there are real use cases of non-power of two min_region_sz. There is no known use case or issue reports from the setup, either. In future, if we find real use cases of non-power of two alignments and we can support it with low enough overhead, we can consider moving the restriction. But, for now, simply disallowing the corner case should be good enough as a hot fix. Fixes: d8f867fa0825 ("mm/damon: add damon_ctx->min_sz_region") Cc: # 6.18.x Signed-off-by: SeongJae Park --- mm/damon/core.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index 925908415a041..55cbf86476006 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -1252,6 +1252,9 @@ int damon_commit_ctx(struct damon_ctx *dst, struct damon_ctx *src) { int err; + if (!is_power_of_2(src->min_region_sz)) + return -EINVAL; + err = damon_commit_schemes(dst, src); if (err) return err; base-commit: 918647226184ca20e5f86ee7d4df3e34c7433799 -- 2.47.3