From patchwork Tue Apr 9 19:22:44 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 13623157 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 84FB8157A66 for ; Tue, 9 Apr 2024 19:24:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712690653; cv=none; b=H47LaGvMVW6U739JEyLLWN4rfPP5lcEx3dgUwLqWqzKXf2jUynMyepeYz+TniSI3Vd4BI5CIkrYrjXr3cR4JF8usqzBXGd/XtqxZBLxUID6vigB9I7Tka4+vASS3LTtgy3NZb3cdLWLCRUmK6cSEYPgfpDkPBMBTFh2WO2j2Vds= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712690653; c=relaxed/simple; bh=er1avreit/gXVooPI/0puJF4i4dYhIIHJ1VQBTIYsoU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=W9yTZV+znAKjpZvdOH6cIFDTtpgoj6DNU4hqkEV2m65OyycmI0r2clegSY50kDx8yx1ApoADTMf5HtVqdGwfdSa9WTST2pQgWJ7Qr0jsyuiIOQy6TEMeNysJB/wHeG3QMmcuR2eZ/IKZRMJjeXjRkufZcJqtRytJfMG01nlPaxE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=ZHSftwi9; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ZHSftwi9" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1712690649; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=xg0rO/waZOgQmZDoxFOYF0uFGKk6lZboizK7nff+LmE=; b=ZHSftwi9tCSU7OBRmZHYJZjWPiIa/XFj1ekDyCpXL9raHOq9vjrbW6k1uAmRWtNEziwYj9 aCt6T7+JFAmv1WjzsON1vrPF3RB7THcPhOyjrHRhviz/BlGnJYhiio2JBLKhwGHVSBHdSB V6JjMlwXcKiKetLstEUBnBQcXI9Y5n4= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-575-RAOsmv4mOp6g3iCo6gpvAQ-1; Tue, 09 Apr 2024 15:24:06 -0400 X-MC-Unique: RAOsmv4mOp6g3iCo6gpvAQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 24D511887313; Tue, 9 Apr 2024 19:23:48 +0000 (UTC) Received: from t14s.redhat.com (unknown [10.39.192.106]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8CD4540AE783; Tue, 9 Apr 2024 19:23:32 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-doc@vger.kernel.org, cgroups@vger.kernel.org, linux-sh@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, David Hildenbrand , Andrew Morton , "Matthew Wilcox (Oracle)" , Peter Xu , Ryan Roberts , Yin Fengwei , Yang Shi , Zi Yan , Jonathan Corbet , Hugh Dickins , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , Chris Zankel , Max Filippov , Muchun Song , Miaohe Lin , Naoya Horiguchi , Richard Chang Subject: [PATCH v1 01/18] mm: allow for detecting underflows with page_mapcount() again Date: Tue, 9 Apr 2024 21:22:44 +0200 Message-ID: <20240409192301.907377-2-david@redhat.com> In-Reply-To: <20240409192301.907377-1-david@redhat.com> References: <20240409192301.907377-1-david@redhat.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.2 Commit 53277bcf126d ("mm: support page_mapcount() on page_has_type() pages") made it impossible to detect mapcount underflows by treating any negative raw mapcount value as a mapcount of 0. We perform such underflow checks in zap_present_folio_ptes() and zap_huge_pmd(), which would currently no longer trigger. Let's check against PAGE_MAPCOUNT_RESERVE instead by using page_type_has_type(), like page_has_type() would, so we can still catch some underflows. Fixes: 53277bcf126d ("mm: support page_mapcount() on page_has_type() pages") Signed-off-by: David Hildenbrand Signed-off-by: David Hildenbrand --- include/linux/mm.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index ef34cf54c14f..0fb8a40f82dd 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1229,11 +1229,10 @@ static inline void page_mapcount_reset(struct page *page) */ static inline int page_mapcount(struct page *page) { - int mapcount = atomic_read(&page->_mapcount) + 1; + int mapcount = atomic_read(&page->_mapcount); /* Handle page_has_type() pages */ - if (mapcount < 0) - mapcount = 0; + mapcount = page_type_has_type(mapcount) ? 0 : mapcount + 1; if (unlikely(PageCompound(page))) mapcount += folio_entire_mapcount(page_folio(page));