Hi, I would like to request that this patch be included in the 4.4 stable tree. It fixes the Bad page state issue discovered at http://oss.sgi.com/archives/xfs/2016-08/msg00617.html ('"Bad page state" errors when calling BULKSTAT under memory pressure?') I tested the patch (no changes needed) by applying it to 4.4.52, running a program to use almost all of my free memory, then running xfs_fsr on a filesystem with > 1.5M files. Before patch: kernel screams with Bad page state / "count:-1" within a minute. After patch: no complaints from the kernel. I repeated the test several times and on another machine that was affected. I have not seen any problems five days later. Thanks, Ivan >From 2aa6ba7b5ad3189cc27f14540aa2f57f0ed8df4b Mon Sep 17 00:00:00 2001 From: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx> Date: Wed, 25 Jan 2017 20:24:57 -0800 Subject: [PATCH] xfs: clear _XBF_PAGES from buffers when readahead page 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 <darrick.wong@xxxxxxxxxx> Reviewed-by: Eric Sandeen <sandeen@xxxxxxxxxx> --- 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 7f0a01f7b592..ac3b4db519df 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -422,6 +422,7 @@ 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; } -- 2.11.0