xfs: ensure f_ffree returned by statfs() is non-negative
Because of delayed updates to sb_icount field in the super block, it
is possible to allocate over maxicount number of inodes. This
causes the arithmetic to calculate a negative number of free inodes
in user commands like df or stat -f.
Since maxicount is a somewhat arbitrary number, a slight over
allocation is not critical but user commands should be displayed as
0 or greater and never go negative. To do this the value in the
stats buffer f_ffree is capped to never go negative.
[ Modified to use max_t as per Christoph's comment. ]
Signed-off-by: Stu Brodsky <sbrodsky@sgi.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
diff --git a/fs/xfs/linux-2.6/xfs_super.c b/fs/xfs/linux-2.6/xfs_super.c
index 15c35b6..c6b24e7 100644
--- a/fs/xfs/linux-2.6/xfs_super.c
+++ b/fs/xfs/linux-2.6/xfs_super.c
@@ -1226,6 +1226,7 @@
struct xfs_inode *ip = XFS_I(dentry->d_inode);
__uint64_t fakeinos, id;
xfs_extlen_t lsize;
+ __int64_t ffree;
statp->f_type = XFS_SB_MAGIC;
statp->f_namelen = MAXNAMELEN - 1;
@@ -1249,7 +1250,11 @@
statp->f_files = min_t(typeof(statp->f_files),
statp->f_files,
mp->m_maxicount);
- statp->f_ffree = statp->f_files - (sbp->sb_icount - sbp->sb_ifree);
+
+ /* make sure statp->f_ffree does not underflow */
+ ffree = statp->f_files - (sbp->sb_icount - sbp->sb_ifree);
+ statp->f_ffree = max_t(__int64_t, ffree, 0);
+
spin_unlock(&mp->m_sb_lock);
if ((ip->i_d.di_flags & XFS_DIFLAG_PROJINHERIT) ||