xfs: detect and fix bad summary counts at mount

Filippo Giunchedi complained that xfs doesn't even perform basic sanity
checks of the fs summary counters at mount time.  Therefore, recalculate
the summary counters from the AGFs after log recovery if the counts were
bad (or we had to recover the fs).  Enhance the recalculation routine to
fail the mount entirely if the new values are also obviously incorrect.

We use a mount state flag to record the "bad summary count" state so
that the (subsequent) online fsck patches can detect subtlely incorrect
counts and set the flag; clear it userspace asks for a repair; or force
a recalculation at the next mount if nobody fixes it by unmount time.

Reported-by: Filippo Giunchedi <fgiunchedi@wikimedia.org>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 18 insertions, 3 deletions

diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
index 350119eeaecb..b3ad15956366 100644
--- a/fs/xfs/libxfs/xfs_sb.c
+++ b/fs/xfs/libxfs/xfs_sb.c
@@ -804,6 +804,7 @@ xfs_initialize_perag_data(
 	uint64_t	bfree = 0;
 	uint64_t	bfreelst = 0;
 	uint64_t	btree = 0;
+	uint64_t	fdblocks;
 	int		error;
 
 	for (index = 0; index < agcount; index++) {
@@ -827,17 +828,31 @@ xfs_initialize_perag_data(
 		btree += pag->pagf_btreeblks;
 		xfs_perag_put(pag);
 	}
+	fdblocks = bfree + bfreelst + btree;
+
+	/*
+	 * If the new summary counts are obviously incorrect, fail the
+	 * mount operation because that implies the AGFs are also corrupt.
+	 * Clear BAD_SUMMARY so that we don't unmount with a dirty log, which
+	 * will prevent xfs_repair from fixing anything.
+	 */
+	if (fdblocks > sbp->sb_dblocks || ifree > ialloc) {
+		xfs_alert(mp, "AGF corruption. Please run xfs_repair.");
+		error = -EFSCORRUPTED;
+		goto out;
+	}
 
 	/* Overwrite incore superblock counters with just-read data */
 	spin_lock(&mp->m_sb_lock);
 	sbp->sb_ifree = ifree;
 	sbp->sb_icount = ialloc;
-	sbp->sb_fdblocks = bfree + bfreelst + btree;
+	sbp->sb_fdblocks = fdblocks;
 	spin_unlock(&mp->m_sb_lock);
 
 	xfs_reinit_percpu_counters(mp);
-
-	return 0;
+out:
+	mp->m_flags &= ~XFS_MOUNT_BAD_SUMMARY;
+	return error;
 }
 
 /*