svn commit: r285021 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs

[Andriy Gapon]

Author: avg
Date: Thu Jul  2 08:32:02 2015
New Revision: 285021
URL: https://svnweb.freebsd.org/changeset/base/285021

Log:
  zfs_mount(MS_REMOUNT): protect zfs_(un)register_callbacks calls
  
  We now take z_teardown_lock as a writer to ensure that there is no I/O
  while the filesystem state is in a flux.  Also, zfs_suspend_fs() ->
  zfsvfs_teardown() call zfs_unregister_callbacks() and zfs_resume_fs() ->
  zfsvfs_setup() call zfs_unregister_callbacks().  Previously there was no
  synchronization between those calls and the calls in the re-mounting
  case.  That could lead to concurrent execution and a crash.
  
  PR:		180060
  Differential Revision:	https://reviews.freebsd.org/D2865
  Suggested by:	mahrens
  Reviewed by:	delphij, pho, mahrens, will
  MFC after:	13 days
  Sponsored by:	ClusterHQ

Modified:
  head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c

Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c	Thu Jul  2 08:25:45 2015	(r285020)
+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c	Thu Jul  2 08:32:02 2015	(r285021)
@@ -1717,9 +1717,19 @@ zfs_mount(vfs_t *vfsp)
 	 * according to those options set in the current VFS options.
 	 */
 	if (vfsp->vfs_flag & MS_REMOUNT) {
-		/* refresh mount options */
-		zfs_unregister_callbacks(vfsp->vfs_data);
+		zfsvfs_t *zfsvfs = vfsp->vfs_data;
+
+		/*
+		 * Refresh mount options with z_teardown_lock blocking I/O while
+		 * the filesystem is in an inconsistent state.
+		 * The lock also serializes this code with filesystem
+		 * manipulations between entry to zfs_suspend_fs() and return
+		 * from zfs_resume_fs().
+		 */
+		rrm_enter(&zfsvfs->z_teardown_lock, RW_WRITER, FTAG);
+		zfs_unregister_callbacks(zfsvfs);
 		error = zfs_register_callbacks(vfsp);
+		rrm_exit(&zfsvfs->z_teardown_lock, FTAG);
 		goto out;
 	}