From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([65.50.211.133]:36239 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750858AbdBBH5Y (ORCPT ); Thu, 2 Feb 2017 02:57:24 -0500 From: Christoph Hellwig Subject: [PATCH 18/19] xfs: clear _XBF_PAGES from buffers when readahead page Date: Thu, 2 Feb 2017 08:56:10 +0100 Message-Id: <1486022171-8076-19-git-send-email-hch@lst.de> In-Reply-To: <1486022171-8076-1-git-send-email-hch@lst.de> References: <1486022171-8076-1-git-send-email-hch@lst.de> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: stable@vger.kernel.org Cc: linux-xfs@vger.kernel.org, "Darrick J. Wong" 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 --- 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 b5b9bff..d7a67d7 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -423,6 +423,7 @@ xfs_buf_allocate_memory( 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; } -- 2.1.4