1 files changed, 35 insertions, 2 deletions

diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 39cf6f3267c3..31453ca0f3dd 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -725,7 +725,7 @@ xfs_mountfs(
         bhv_vnode_t     *rvp = NULL;
         int             readio_log, writeio_log;
         xfs_daddr_t     d;
-        __uint64_t      ret64;
+        __uint64_t      resblks;
         __int64_t       update_flags;
         uint            quotamount, quotaflags;
         int             agno;
@@ -842,6 +842,7 @@ xfs_mountfs(
          */
         if ((mfsi_flags & XFS_MFSI_SECOND) == 0 &&
             (mp->m_flags & XFS_MOUNT_NOUUID) == 0) {
+                __uint64_t      ret64;
                 if (xfs_uuid_mount(mp)) {
                         error = XFS_ERROR(EINVAL);
                         goto error1;
@@ -1135,13 +1136,27 @@ xfs_mountfs(
                 goto error4;
         }
 
-
         /*
          * Complete the quota initialisation, post-log-replay component.
          */
         if ((error = XFS_QM_MOUNT(mp, quotamount, quotaflags, mfsi_flags)))
                 goto error4;
 
+        /*
+         * Now we are mounted, reserve a small amount of unused space for
+         * privileged transactions. This is needed so that transaction
+         * space required for critical operations can dip into this pool
+         * when at ENOSPC. This is needed for operations like create with
+         * attr, unwritten extent conversion at ENOSPC, etc. Data allocations
+         * are not allowed to use this reserved space.
+         *
+         * We default to 5% or 1024 fsbs of space reserved, whichever is smaller.
+         * This may drive us straight to ENOSPC on mount, but that implies
+         * we were already there on the last unmount.
+         */
+        resblks = min_t(__uint64_t, mp->m_sb.sb_dblocks / 20, 1024);
+        xfs_reserve_blocks(mp, &resblks, NULL);
+
         return 0;
 
  error4:
@@ -1181,6 +1196,7 @@ xfs_unmountfs(xfs_mount_t *mp, struct cred *cr)
 #if defined(DEBUG) || defined(INDUCE_IO_ERROR)
         int64_t         fsid;
 #endif
+        __uint64_t      resblks;
 
         /*
          * We can potentially deadlock here if we have an inode cluster
@@ -1209,6 +1225,23 @@ xfs_unmountfs(xfs_mount_t *mp, struct cred *cr)
                 xfs_binval(mp->m_rtdev_targp);
         }
 
+        /*
+         * Unreserve any blocks we have so that when we unmount we don't account
+         * the reserved free space as used. This is really only necessary for
+         * lazy superblock counting because it trusts the incore superblock
+         * counters to be aboslutely correct on clean unmount.
+         *
+         * We don't bother correcting this elsewhere for lazy superblock
+         * counting because on mount of an unclean filesystem we reconstruct the
+         * correct counter value and this is irrelevant.
+         *
+         * For non-lazy counter filesystems, this doesn't matter at all because
+         * we only every apply deltas to the superblock and hence the incore
+         * value does not matter....
+         */
+        resblks = 0;
+        xfs_reserve_blocks(mp, &resblks, NULL);
+
         xfs_log_sbcount(mp, 1);
         xfs_unmountfs_writesb(mp);
         xfs_unmountfs_wait(mp);                 /* wait for async bufs */