From patchwork Wed Feb 8 14:53:35 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthew Wilcox X-Patchwork-Id: 13133136 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 683F9C636D7 for ; Wed, 8 Feb 2023 14:53:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231573AbjBHOxw (ORCPT ); Wed, 8 Feb 2023 09:53:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60674 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231566AbjBHOxv (ORCPT ); Wed, 8 Feb 2023 09:53:51 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D0A0872BD; Wed, 8 Feb 2023 06:53:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Transfer-Encoding:MIME-Version: References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From:Sender:Reply-To: Content-Type:Content-ID:Content-Description; bh=HdngZPvdXKZlg8aWQlwaqgB89GRwI5fL2TphFM1bPZg=; b=mIOoo7xcGsiBchVCgVhbLA4GaO maepzfffPhFBJh1ZKAHeGTvMELGTvkEl1c5Pd5Ozj2+WhTRZx5zJhWSjhMJuicBsK3oVsqPUYMhir uhf0TZjF4cHNOgF+dXtJ10FaVGNsWhu0m47+EYSn3La4I863Krw849ee81FyoWUx3PJAUiIHGTEx4 t3Jhl1tgNZhpQvFDRvqar4cn/H8ZeaFrvvVzrNlGj97rXB3vggM1iZ+jaPHHIv5QuHYkSemgA2mQN SGpnygNsMm2kdC4RlP/rI5FyFdlvpYKAB2nQNKgD9zG2/T9PP+JHqyc7/ih3F9IQX2KMX6ueG+rhe QO25gZLw==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pPlpL-001HwV-1L; Wed, 08 Feb 2023 14:53:39 +0000 From: "Matthew Wilcox (Oracle)" To: linux-xfs@vger.kernel.org, linux-afs@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Cc: "Matthew Wilcox (Oracle)" Subject: [PATCH 3/3] mm: Hold the RCU read lock over calls to ->map_pages Date: Wed, 8 Feb 2023 14:53:35 +0000 Message-Id: <20230208145335.307287-4-willy@infradead.org> X-Mailer: git-send-email 2.37.1 In-Reply-To: <20230208145335.307287-1-willy@infradead.org> References: <20230208145335.307287-1-willy@infradead.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org Prevent filesystems from doing things which sleep in their map_pages method. This is in preparation for a pagefault path protected only by RCU. Signed-off-by: Matthew Wilcox (Oracle) --- Documentation/filesystems/locking.rst | 4 ++-- mm/memory.c | 7 ++++++- 2 files changed, 8 insertions(+), 3 deletions(-) diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst index 922886fefb7f..8a80390446ba 100644 --- a/Documentation/filesystems/locking.rst +++ b/Documentation/filesystems/locking.rst @@ -645,7 +645,7 @@ ops mmap_lock PageLocked(page) open: yes close: yes fault: yes can return with page locked -map_pages: yes +map_pages: read page_mkwrite: yes can return with page locked pfn_mkwrite: yes access: yes @@ -661,7 +661,7 @@ locked. The VM will unlock the page. ->map_pages() is called when VM asks to map easy accessible pages. Filesystem should find and map pages associated with offsets from "start_pgoff" -till "end_pgoff". ->map_pages() is called with page table locked and must +till "end_pgoff". ->map_pages() is called with the RCU lock held and must not block. If it's not possible to reach a page without blocking, filesystem should skip it. Filesystem should use set_pte_range() to setup page table entry. Pointer to entry associated with the page is passed in diff --git a/mm/memory.c b/mm/memory.c index f1cf47b7e3bb..77577a1d09ac 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4442,6 +4442,7 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf) unsigned long address = vmf->address, nr_pages, mask; pgoff_t start_pgoff = vmf->pgoff; pgoff_t end_pgoff; + vm_fault_t ret; int off; nr_pages = READ_ONCE(fault_around_bytes) >> PAGE_SHIFT; @@ -4467,7 +4468,11 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf) return VM_FAULT_OOM; } - return vmf->vma->vm_ops->map_pages(vmf, start_pgoff, end_pgoff); + rcu_read_lock(); + ret = vmf->vma->vm_ops->map_pages(vmf, start_pgoff, end_pgoff); + rcu_read_unlock(); + + return ret; } /* Return true if we should do read fault-around, false otherwise */