From: Darrick J. Wong Date: Thu, 26 Jan 2017 04:24:57 +0000 (-0800) Subject: xfs: clear _XBF_PAGES from buffers when readahead page X-Git-Tag: release-20171130_firefly~4^2~100^2~1^2~20^2~22 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=6d43e485e0067b682466eb4e3aff8ff9a6822966;p=firefly-linux-kernel-4.4.55.git xfs: clear _XBF_PAGES from buffers when readahead page 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 --- diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index eb1b8c8acfcb..8146b0cf20ce 100644 --- 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; }