Fix 'zfs rollback' on mounted file systems

Rolling back a mounted filesystem with open file handles and
cached dentries+inodes never worked properly in ZoL.  The
major issue was that Linux provides no easy mechanism for
modules to invalidate the inode cache for a file system.

Because of this it was possible that an inode from the previous
filesystem would not get properly dropped from the cache during
rolling back.  Then a new inode with the same inode number would
be create and collide with the existing cached inode.  Ideally
this would trigger an VERIFY() but in practice the error wasn't
handled and it would just NULL reference.

Luckily, this issue can be resolved by sprucing up the existing
Solaris zfs_rezget() functionality for the Linux VFS.

The way it works now is that when a file system is rolled back
all the cached inodes will be traversed and refetched from disk.
If a version of the cached inode exists on disk the in-core
copy will be updated accordingly.  If there is no match for that
object on disk it will be unhashed from the inode cache and
marked as stale.

This will effectively make the inode unfindable for lookups
allowing the inode number to be immediately recycled.  The inode
will then only be accessible from the cached dentries.  Subsequent
dentry lookups which reference a stale inode will result in the
dentry being invalidated.  Once invalidated the dentry will drop
its reference on the inode allowing it to be safely pruned from
the cache.

Special care is taken for negative dentries since they do not
reference any inode.  These dentires will be invalidate based
on when they were added to the dentry cache.  Entries added
before the last rollback will be invalidate to prevent them
from masking real files in the dataset.

Two nice side effects of this fix are:

* Removes the dependency on spl_invalidate_inodes(), it can now
  be safely removed from the SPL when we choose to do so.

* zfs_znode_alloc() no longer requires a dentry to be passed.
  This effectively reverts this portition of the code to its
  upstream counterpart.  The dentry is not instantiated more
  correctly in the Linux ZPL layer.

Signed-off-by: Brian Behlendorf <[email protected]>
Signed-off-by: Ned Bass <[email protected]>
Closes #795

1 files changed, 26 insertions, 18 deletions

diff --git a/module/zfs/zfs_vfsops.c b/module/zfs/zfs_vfsops.c
index fc5c2ba39..ac5c317ce 100644
--- a/module/zfs/zfs_vfsops.c
+++ b/module/zfs/zfs_vfsops.c
@@ -1032,7 +1032,7 @@ EXPORT_SYMBOL(zfs_sb_prune);
 #endif /* HAVE_SHRINK */
 
 /*
- * Teardown the zfs_sb_t::z_os.
+ * Teardown the zfs_sb_t.
  *
  * Note, if 'unmounting' if FALSE, we return with the 'z_teardown_lock'
  * and 'z_teardown_inactive_lock' held.
@@ -1053,7 +1053,6 @@ zfs_sb_teardown(zfs_sb_t *zsb, boolean_t unmounting)
 		 * for non-snapshots.
 		 */
 		shrink_dcache_sb(zsb->z_parent->z_sb);
-		(void) spl_invalidate_inodes(zsb->z_parent->z_sb, 0);
 	}
 
 	/*
@@ -1079,25 +1078,26 @@ zfs_sb_teardown(zfs_sb_t *zsb, boolean_t unmounting)
 	}
 
 	/*
-	 * At this point there are no vops active, and any new vops will
-	 * fail with EIO since we have z_teardown_lock for writer (only
-	 * relavent for forced unmount).
+	 * At this point there are no VFS ops active, and any new VFS ops
+	 * will fail with EIO since we have z_teardown_lock for writer (only
+	 * relevant for forced unmount).
 	 *
 	 * Release all holds on dbufs.
 	 */
 	mutex_enter(&zsb->z_znodes_lock);
 	for (zp = list_head(&zsb->z_all_znodes); zp != NULL;
-	    zp = list_next(&zsb->z_all_znodes, zp))
+	    zp = list_next(&zsb->z_all_znodes, zp)) {
 		if (zp->z_sa_hdl) {
 			ASSERT(atomic_read(&ZTOI(zp)->i_count) > 0);
 			zfs_znode_dmu_fini(zp);
 		}
+	}
 	mutex_exit(&zsb->z_znodes_lock);
 
 	/*
-	 * If we are unmounting, set the unmounted flag and let new vops
+	 * If we are unmounting, set the unmounted flag and let new VFS ops
 	 * unblock.  zfs_inactive will have the unmounted behavior, and all
-	 * other vops will fail with EIO.
+	 * other VFS ops will fail with EIO.
 	 */
 	if (unmounting) {
 		zsb->z_unmounted = B_TRUE;
@@ -1392,7 +1392,7 @@ zfs_vget(struct super_block *sb, struct inode **ipp, fid_t *fidp)
 EXPORT_SYMBOL(zfs_vget);
 
 /*
- * Block out VOPs and close zfs_sb_t::z_os
+ * Block out VFS ops and close zfs_sb_t
  *
  * Note, if successful, then we return with the 'z_teardown_lock' and
  * 'z_teardown_inactive_lock' write held.
@@ -1404,6 +1404,7 @@ zfs_suspend_fs(zfs_sb_t *zsb)
 
 	if ((error = zfs_sb_teardown(zsb, B_FALSE)) != 0)
 		return (error);
+
 	dmu_objset_disown(zsb->z_os, zsb);
 
 	return (0);
@@ -1411,7 +1412,7 @@ zfs_suspend_fs(zfs_sb_t *zsb)
 EXPORT_SYMBOL(zfs_suspend_fs);
 
 /*
- * Reopen zfs_sb_t::z_os and release VOPs.
+ * Reopen zfs_sb_t and release VFS ops.
  */
 int
 zfs_resume_fs(zfs_sb_t *zsb, const char *osname)
@@ -1440,30 +1441,37 @@ zfs_resume_fs(zfs_sb_t *zsb, const char *osname)
 			goto bail;
 
 		VERIFY(zfs_sb_setup(zsb, B_FALSE) == 0);
+		zsb->z_rollback_time = jiffies;
 
 		/*
-		 * Attempt to re-establish all the active znodes with
-		 * their dbufs.  If a zfs_rezget() fails, then we'll let
-		 * any potential callers discover that via ZFS_ENTER_VERIFY_VP
-		 * when they try to use their znode.
+		 * Attempt to re-establish all the active inodes with their
+		 * dbufs.  If a zfs_rezget() fails, then we unhash the inode
+		 * and mark it stale.  This prevents a collision if a new
+		 * inode/object is created which must use the same inode
+		 * number.  The stale inode will be be released when the
+		 * VFS prunes the dentry holding the remaining references
+		 * on the stale inode.
 		 */
 		mutex_enter(&zsb->z_znodes_lock);
 		for (zp = list_head(&zsb->z_all_znodes); zp;
 		    zp = list_next(&zsb->z_all_znodes, zp)) {
-			(void) zfs_rezget(zp);
+			err2 = zfs_rezget(zp);
+			if (err2) {
+				remove_inode_hash(ZTOI(zp));
+				zp->z_is_stale = B_TRUE;
+			}
 		}
 		mutex_exit(&zsb->z_znodes_lock);
-
 	}
 
 bail:
-	/* release the VOPs */
+	/* release the VFS ops */
 	rw_exit(&zsb->z_teardown_inactive_lock);
 	rrw_exit(&zsb->z_teardown_lock, FTAG);
 
 	if (err) {
 		/*
-		 * Since we couldn't reopen zfs_sb_t::z_os, force
+		 * Since we couldn't reopen zfs_sb_t, force
 		 * unmount this file system.
 		 */
 		(void) zfs_umount(zsb->z_sb);