Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752611AbdFSSep (ORCPT + 2 others); Mon, 19 Jun 2017 14:34:45 -0400 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:51888 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750869AbdFSSem (ORCPT ); Mon, 19 Jun 2017 14:34:42 -0400 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux@roeck-us.net Cc: "Darrick J. Wong" , Ivan Kozik , Jiri Slaby , Willy Tarreau Subject: [PATCH 3.10 063/268] xfs: clear _XBF_PAGES from buffers when readahead page Date: Mon, 19 Jun 2017 20:29:22 +0200 Message-Id: <1497897167-14556-64-git-send-email-w@1wt.eu> X-Mailer: git-send-email 2.8.0.rc2.1.gbe9624a In-Reply-To: <1497897167-14556-1-git-send-email-w@1wt.eu> References: <1497897167-14556-1-git-send-email-w@1wt.eu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: 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: Jiri Slaby Signed-off-by: Willy Tarreau --- fs/xfs/xfs_buf.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index 1b2472a..8ff89db 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -428,6 +428,7 @@ 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; } -- 2.8.0.rc2.1.gbe9624a