From 8e69ce147127a0235e8d1f2b75ea214be78c61b3 Mon Sep 17 00:00:00 2001 From: Eric Sandeen Date: Fri, 25 Sep 2009 19:42:26 +0000 Subject: [PATCH] fix readahead calculations in xfs_dir2_leaf_getdents() This is for bug #850, http://oss.sgi.com/bugzilla/show_bug.cgi?id=850 XFS file system segfaults , repeatedly and 100% reproducable in 2.6.30 , 2.6.31 The above only showed up on a CONFIG_XFS_DEBUG=y kernel, because xfs_bmapi() ASSERTs that it has been asked for at least one map, and it was getting 0. The root cause is that our guesstimated "bufsize" from xfs_file_readdir was fairly small, and the bufsize -= length; in the loop was going negative - except bufsize is a size_t, so it was wrapping to a very large number. Then when we did ra_want = howmany(bufsize + mp->m_dirblksize, mp->m_sb.sb_blocksize) - 1; with that very large number, the (int) ra_want was coming out negative, and a subsequent compare: if (1 + ra_want > map_blocks ... was coming out -true- (negative int compare w/ uint) and we went back to xfs_bmapi() for more, even though we did not need more, and asked for 0 maps, and hit the ASSERT. We have kind of a type mess here, but just keeping bufsize from going negative is probably sufficient to avoid the problem. Signed-off-by: Eric Sandeen Reviewed-by: Christoph Hellwig Reviewed-by: Alex Elder Signed-off-by: Alex Elder --- fs/xfs/xfs_dir2_leaf.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/xfs/xfs_dir2_leaf.c b/fs/xfs/xfs_dir2_leaf.c index fa913e459442..41ad537c49e9 100644 --- a/fs/xfs/xfs_dir2_leaf.c +++ b/fs/xfs/xfs_dir2_leaf.c @@ -854,6 +854,7 @@ xfs_dir2_leaf_getdents( */ ra_want = howmany(bufsize + mp->m_dirblksize, mp->m_sb.sb_blocksize) - 1; + ASSERT(ra_want >= 0); /* * If we don't have as many as we want, and we haven't @@ -1088,7 +1089,8 @@ xfs_dir2_leaf_getdents( */ ptr += length; curoff += length; - bufsize -= length; + /* bufsize may have just been a guess; don't go negative */ + bufsize = bufsize > length ? bufsize - length : 0; } /*