Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753332AbdC1MfD (ORCPT ); Tue, 28 Mar 2017 08:35:03 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:59082 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752379AbdC1MfA (ORCPT ); Tue, 28 Mar 2017 08:35:00 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Darrick J. Wong" , Eric Sandeen , Ivan Kozik Subject: [PATCH 4.4 55/76] xfs: clear _XBF_PAGES from buffers when readahead page Date: Tue, 28 Mar 2017 14:30:52 +0200 Message-Id: <20170328122602.178338836@linuxfoundation.org> X-Mailer: git-send-email 2.12.1 In-Reply-To: <20170328122559.966310440@linuxfoundation.org> References: <20170328122559.966310440@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1645 Lines: 46 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Darrick J. Wong commit 2aa6ba7b5ad3189cc27f14540aa2f57f0ed8df4b upstream. If we try to allocate memory pages to back an xfs_buf that we're trying to read, it's possible that we'll be so short on memory that the page allocation fails. For a blocking read we'll just wait, but for readahead we simply dump all the pages we've collected so far. Unfortunately, after dumping the pages we neglect to clear the _XBF_PAGES state, which means that the subsequent call to xfs_buf_free thinks that b_pages still points to pages we own. It then double-frees the b_pages pages. This results in screaming about negative page refcounts from the memory manager, which xfs oughtn't be triggering. To reproduce this case, mount a filesystem where the size of the inodes far outweighs the availalble memory (a ~500M inode filesystem on a VM with 300MB memory did the trick here) and run bulkstat in parallel with other memory eating processes to put a huge load on the system. The "check summary" phase of xfs_scrub also works for this purpose. Signed-off-by: Darrick J. Wong Reviewed-by: Eric Sandeen Cc: Ivan Kozik Signed-off-by: Greg Kroah-Hartman --- fs/xfs/xfs_buf.c | 1 + 1 file changed, 1 insertion(+) --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -375,6 +375,7 @@ retry: out_free_pages: for (i = 0; i < bp->b_page_count; i++) __free_page(bp->b_pages[i]); + bp->b_flags &= ~_XBF_PAGES; return error; }