From patchwork Tue Feb 25 21:48:28 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthew Wilcox X-Patchwork-Id: 11404815 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 0B9F61395 for ; Tue, 25 Feb 2020 21:51:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DFB12222C2 for ; Tue, 25 Feb 2020 21:51:05 +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="CsHGUAep" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729644AbgBYVup (ORCPT ); Tue, 25 Feb 2020 16:50:45 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:43534 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729065AbgBYVsm (ORCPT ); Tue, 25 Feb 2020 16:48:42 -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=rMcV50ueBpteR9LXkwAudPimKgybkJUfXQ/lOrRcnKc=; b=CsHGUAep6LhQaabD2KWiIEV0lW 8DzIJa2XG+iXaLddhcZ23/dmd2k5EZnrcQ74J51wciR1hgoSNbc07DtcMBmJjf8yyCvZ6/Ye2/fu2 WTYV8ip/Zgyetuqd6clnSc5g/hOOXCbR2cV1Zuelv24mymOSeD/9fW28DdjpprDygAIt51QdbcBFc CuE2dNblQkzefXmFZ674DMRoBtzt4iQHjZzP/0qEqWOOuHJ+VL1dUl/8KeQCv5Mr7B05kR/SFysTl tRi9sSlJITXI8GhIQCORoNBQ8NnvPpLbqtyiyjOYMlqjf2s1PoAZU8yLlEPjQupkO5XyPWMVw+y/j gwcVsQxQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j6i4H-0007qB-Dl; Tue, 25 Feb 2020 21:48:41 +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 v8 15/25] mm: Use memalloc_nofs_save in readahead path Date: Tue, 25 Feb 2020 13:48:28 -0800 Message-Id: <20200225214838.30017-16-willy@infradead.org> X-Mailer: git-send-email 2.21.1 In-Reply-To: <20200225214838.30017-1-willy@infradead.org> References: <20200225214838.30017-1-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 0afb55a49909..7f2d54fb1691 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -22,6 +22,7 @@ #include #include #include +#include #include "internal.h" @@ -185,6 +186,18 @@ 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. */ @@ -229,6 +242,7 @@ void page_cache_readahead_unbounded(struct address_space *mapping, * will then handle the error. */ read_pages(&rac, &page_pool, false); + memalloc_nofs_restore(nofs); } EXPORT_SYMBOL_GPL(page_cache_readahead_unbounded);