From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5EC67CE79A9 for ; Wed, 20 Sep 2023 02:18:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231624AbjITCSq (ORCPT ); Tue, 19 Sep 2023 22:18:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47874 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229521AbjITCSp (ORCPT ); Tue, 19 Sep 2023 22:18:45 -0400 Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EB7C1BE for ; Tue, 19 Sep 2023 19:18:39 -0700 (PDT) Received: from imladris.home.surriel.com ([10.0.13.28] helo=imladris.surriel.com) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1qimn9-0006me-2W; Tue, 19 Sep 2023 22:18:15 -0400 From: riel@surriel.com To: linux-kernel@vger.kernel.org Cc: kernel-team@meta.com, linux-mm@kvack.org, akpm@linux-foundation.org, muchun.song@linux.dev, mike.kravetz@oracle.com, leit@meta.com Subject: [PATCH 0/2] hugetlbfs: close race between MADV_DONTNEED and page fault Date: Tue, 19 Sep 2023 22:16:08 -0400 Message-ID: <20230920021811.3095089-1-riel@surriel.com> X-Mailer: git-send-email 2.41.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: riel@surriel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Malloc libraries, like jemalloc and tcalloc, take decisions on when to call madvise independently from the code in the main application. This sometimes results in the application page faulting on an address, right after the malloc library has shot down the backing memory with MADV_DONTNEED. Usually this is harmless, because we always have some 4kB pages sitting around to satisfy a page fault. However, with hugetlbfs systems often allocate only the exact number of huge pages that the application wants. Due to TLB batching, hugetlbfs MADV_DONTNEED will free pages outside of any lock taken on the page fault path, which can open up the following race condition: CPU 1 CPU 2 MADV_DONTNEED unmap page shoot down TLB entry page fault fail to allocate a huge page killed with SIGBUS free page Fix that race by extending the hugetlb_vma_lock locking scheme to also cover private hugetlb mappings (with resv_map), and pulling the locking from __unmap_hugepage_final_range into helper functions called from zap_page_range_single. This ensures page faults stay locked out of the MADV_DONTNEED VMA until the huge pages have actually been freed.