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 3E7CE32B115; Thu, 21 May 2026 03:54:00 +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=1779335641; cv=none; b=uA1Xp6GkPt8D2kGHEgf60GsMb6ZE0z5XYEosrxirti1XFEYvDU0IGp9AD1cRXBmIWrEHDuIoyQOdNn2vqCG1HBlAXlGEzDPAu+NCyupoycMxF8DQhrMdDus7Ij64+XkygM68rND5BlmAUIwTPs20TJlDWq6ENjWl4QeATQLuwOY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779335641; c=relaxed/simple; bh=8B9IiCSCXwYFGO3g7QwEtxLcmC3JtXQgAOF4um9StEY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tR5bxzAHHhrIEUlFWpvkxy1OuYaZcM2ArS4ayjuhTEB8f2QF5F+NzsOHZFIjCiMH/HgsPatCnN/EBKrhsA+3D8wFBhNhoAf8sq0Y6pCYelqok1jBH7ejS2S2+UZPNPvh1JIxCAtyUl7OmR015YIHJuH/MKdn7BpIgraKeF5bl6Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=S5iXL/C1; 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="S5iXL/C1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DB5621F00A3C; Thu, 21 May 2026 03:53:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779335640; bh=5i2WVbg2PjBsmn2NfpjKEh0VGjqNajgL/l9BFto2EhQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=S5iXL/C1blLg/GyK2CQmNtbMwDPo3AXZFESdgEudrFXr0+gB4eLnW/2CoeEHiVVg/ CgaueD1eASKKsZ7KwUpa2CtfZAQDOc8zkPdwxVaKguWFWFXjaTv0uaCKWN3pSnW7O+ bDJLwVwwIv6EmwrNXqa6feOMeC5OE3lVNUmzwR18x6lHQl1NhFuNDIBEGVi/f7O9/Y w+gDlv5V418PkQ5CYft9a9NKngoHUJjmjL9qoSTcDB383HBoZDD9sP+3Mh9UHuyFq9 E0S7nHA4yfQZAaM6YMdVdxPiB9BmfzwprER6t42CCeZK6TLj0rDPrQaoc4futrNIbY dyaxOhRY6+J2Q== From: SeongJae Park To: Cc: SeongJae Park , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH v1.1 01/14] mm/damon/core: safely handle no region case in damon_set_regions() Date: Wed, 20 May 2026 20:53:35 -0700 Message-ID: <20260521035349.87565-2-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260521035349.87565-1-sj@kernel.org> References: <20260521035349.87565-1-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_set_regions() calls damon_first_region() regardless of the number of DAMON regions in a given DAMON target. damon_first_region() internally uses list_first_entry(), which clearly documents the list is expected to be not empty. Due to the internal implementation of the macro, damon_set_regions() is safe for now. But the internal implementation of the macro can be changed in future. Refactor the function to explicitly and safely handle the empty region list case without depending on the internal implementation. No behavioral change is intended. Signed-off-by: SeongJae Park --- mm/damon/core.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index 0267faf216b95..40946a7f6f549 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -356,6 +356,19 @@ int damon_set_regions(struct damon_target *t, struct damon_addr_range *ranges, damon_destroy_region(r, t); } + if (!damon_nr_regions(t)) { + for (i = 0; i < nr_ranges; i++) { + r = damon_new_region( + ALIGN_DOWN(ranges[i].start, + min_region_sz), + ALIGN(ranges[i].end, min_region_sz)); + if (!r) + return -ENOMEM; + damon_add_region(r, t); + } + return 0; + } + r = damon_first_region(t); /* Add new regions or resize existing regions to fit in the ranges */ for (i = 0; i < nr_ranges; i++) { -- 2.47.3