Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.9 50/51] xfs: clear _XBF_PAGES from buffers when readahead page | Date | Thu, 2 Feb 2017 19:38:09 +0100 |
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4.9-stable review patch. If anyone has any objections, please let me know.
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From: "Darrick J. Wong" <darrick.wong@oracle.com>
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 <darrick.wong@oracle.com> Reviewed-by: Eric Sandeen <sandeen@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- fs/xfs/xfs_buf.c | 1 + 1 file changed, 1 insertion(+)
--- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -423,6 +423,7 @@ 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; }
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