From patchwork Wed Feb 19 21:01:03 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthew Wilcox X-Patchwork-Id: 11392643 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 25FB8109A for ; Wed, 19 Feb 2020 21:02:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 06CC624673 for ; Wed, 19 Feb 2020 21:02:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="F3kXDDpZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728116AbgBSVCt (ORCPT ); Wed, 19 Feb 2020 16:02:49 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:35924 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727649AbgBSVBG (ORCPT ); Wed, 19 Feb 2020 16:01:06 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=xVXe2mHxuFlpJauTFAREACgBtskK8JQqv16NulPdwMo=; b=F3kXDDpZ016zj77nzf3xs9HNhB c39hgvEiXMXpDmXJJghRyVbQMd9bQMtSAzeQLHly/ybPqD2ydVSEI4rkiaB9n4MrV5lJMO5TAOHpT LsA4+sqAh3sjH6idXLPtUndMdxvuT67kL2DMo4IotYTvlEvyNqU15dBP/gmtAHMJiYi1zlhefB+pQ okljimRMCao3QCzBUAxBJQKIRfcethiQohvU/9XCsH/VS+Vpp+HAgX2+R1ONMyFmghwTrN6Tmau8B beKkIxg+LolJhz+78XZwS7VZsuxlQ7gLLHa+AyMl78a/LXsGBf7EVWA8feUeASUtSsf4m1jAST6h0 JPdvTb6Q==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j4WSv-0008Ve-Kf; Wed, 19 Feb 2020 21:01:05 +0000 From: Matthew Wilcox To: linux-fsdevel@vger.kernel.org Cc: "Matthew Wilcox (Oracle)" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, ocfs2-devel@oss.oracle.com, linux-xfs@vger.kernel.org, Cong Wang , Michal Hocko Subject: [PATCH v7 24/24] mm: Use memalloc_nofs_save in readahead path Date: Wed, 19 Feb 2020 13:01:03 -0800 Message-Id: <20200219210103.32400-25-willy@infradead.org> X-Mailer: git-send-email 2.21.1 In-Reply-To: <20200219210103.32400-1-willy@infradead.org> References: <20200219210103.32400-1-willy@infradead.org> MIME-Version: 1.0 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org From: "Matthew Wilcox (Oracle)" Ensure that memory allocations in the readahead path do not attempt to reclaim file-backed pages, which could lead to a deadlock. It is possible, though unlikely this is the root cause of a problem observed by Cong Wang. Signed-off-by: Matthew Wilcox (Oracle) Reported-by: Cong Wang Suggested-by: Michal Hocko --- mm/readahead.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/mm/readahead.c b/mm/readahead.c index bbe7208fcc2d..9fb5f77dcf69 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -22,6 +22,7 @@ #include #include #include +#include #include "internal.h" @@ -186,6 +187,18 @@ void page_cache_readahead_unbounded(struct address_space *mapping, }; unsigned long i; + /* + * Partway through the readahead operation, we will have added + * locked pages to the page cache, but will not yet have submitted + * them for I/O. Adding another page may need to allocate memory, + * which can trigger memory reclaim. Telling the VM we're in + * the middle of a filesystem operation will cause it to not + * touch file-backed pages, preventing a deadlock. Most (all?) + * filesystems already specify __GFP_NOFS in their mapping's + * gfp_mask, but let's be explicit here. + */ + unsigned int nofs = memalloc_nofs_save(); + /* * Preallocate as many pages as we will need. */ @@ -230,6 +243,7 @@ void page_cache_readahead_unbounded(struct address_space *mapping, * will then handle the error. */ read_pages(&rac, &page_pool); + memalloc_nofs_restore(nofs); } EXPORT_SYMBOL_GPL(page_cache_readahead_unbounded);