Provide vfs suspension support only for filesystems which need it, take

two.

nullfs and unionfs need to request suspension if underlying filesystem(s)
use it. Utilize mnt_kern_flag for this purpose.

This is a fixup for 273271.

No strong objections from: kib
Pointy hat to: mjg
MFC after:	2 weeks

6 files changed, 18 insertions, 16 deletions

diff --git a/sys/fs/nullfs/null_vfsops.c b/sys/fs/nullfs/null_vfsops.c
index 80824a5..fd3d385 100644
--- a/sys/fs/nullfs/null_vfsops.c
+++ b/sys/fs/nullfs/null_vfsops.c
@@ -198,6 +198,8 @@ nullfs_mount(struct mount *mp)
 		    MNTK_EXTENDED_SHARED);
 	}
 	mp->mnt_kern_flag |= MNTK_LOOKUP_EXCL_DOTDOT;
+	mp->mnt_kern_flag |= lowerrootvp->v_mount->mnt_kern_flag &
+	    MNTK_SUSPENDABLE;
 	MNT_IUNLOCK(mp);
 	mp->mnt_data = xmp;
 	vfs_getnewfsid(mp);
diff --git a/sys/fs/tmpfs/tmpfs_vfsops.c b/sys/fs/tmpfs/tmpfs_vfsops.c
index f0bb96b..4777234 100644
--- a/sys/fs/tmpfs/tmpfs_vfsops.c
+++ b/sys/fs/tmpfs/tmpfs_vfsops.c
@@ -255,6 +255,7 @@ tmpfs_mount(struct mount *mp)
 
 	MNT_ILOCK(mp);
 	mp->mnt_flag |= MNT_LOCAL;
+	mp->mnt_kern_flag |= MNTK_SUSPENDABLE;
 	MNT_IUNLOCK(mp);
 
 	mp->mnt_data = tmp;
@@ -427,14 +428,6 @@ tmpfs_sync(struct mount *mp, int waitfor)
 }
 
 /*
- * A stub created so that vfs does vn_start_write for this filesystem
- */
-static void
-tmpfs_susp_clean(struct mount *mp)
-{
-}
-
-/*
  * tmpfs vfs operations.
  */
 
@@ -445,6 +438,5 @@ struct vfsops tmpfs_vfsops = {
 	.vfs_statfs =			tmpfs_statfs,
 	.vfs_fhtovp =			tmpfs_fhtovp,
 	.vfs_sync =			tmpfs_sync,
-	.vfs_susp_clean =		tmpfs_susp_clean,
 };
 VFS_SET(tmpfs_vfsops, tmpfs, VFCF_JAIL);
diff --git a/sys/fs/unionfs/union_vfsops.c b/sys/fs/unionfs/union_vfsops.c
index c60b02c..e4b9fb5 100644
--- a/sys/fs/unionfs/union_vfsops.c
+++ b/sys/fs/unionfs/union_vfsops.c
@@ -297,6 +297,13 @@ unionfs_domount(struct mount *mp)
 	if ((ump->um_lowervp->v_mount->mnt_flag & MNT_LOCAL) &&
 	    (ump->um_uppervp->v_mount->mnt_flag & MNT_LOCAL))
 		mp->mnt_flag |= MNT_LOCAL;
+
+	/*
+	 * Check mnt_kern_flag
+	 */
+	if ((ump->um_lowervp->v_mount->mnt_flag & MNTK_SUSPENDABLE) ||
+	    (ump->um_uppervp->v_mount->mnt_flag & MNTK_SUSPENDABLE))
+		mp->mnt_kern_flag |= MNTK_SUSPENDABLE;
 	MNT_IUNLOCK(mp);
 
 	/*
diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
index 7a72137..b3e1c3b 100644
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -1576,7 +1576,7 @@ static bool
 vn_suspendable_mp(struct mount *mp)
 {
 
-	return (mp->mnt_op->vfs_susp_clean != NULL);
+	return ((mp->mnt_kern_flag & MNTK_SUSPENDABLE) != 0);
 }
 
 static bool
diff --git a/sys/sys/mount.h b/sys/sys/mount.h
index 633c6db..c4e1145 100644
--- a/sys/sys/mount.h
+++ b/sys/sys/mount.h
@@ -361,7 +361,7 @@ void          __mnt_vnode_markerfree_active(struct vnode **mvp, struct mount *);
 #define	MNTK_SUSPEND	0x08000000	/* request write suspension */
 #define	MNTK_SUSPEND2	0x04000000	/* block secondary writes */
 #define	MNTK_SUSPENDED	0x10000000	/* write operations are suspended */
-#define	MNTK_UNUSED25	0x20000000	/*  --available-- */
+#define	MNTK_SUSPENDABLE	0x20000000 /* writes can be suspended */
 #define MNTK_LOOKUP_SHARED	0x40000000 /* FS supports shared lock lookups */
 #define	MNTK_NOKNOTE	0x80000000	/* Don't send KNOTEs from VOP hooks */
 
@@ -754,10 +754,11 @@ vfs_statfs_t	__vfs_statfs;
 	_rc; })
 
 #define	VFS_SUSP_CLEAN(MP) do {						\
-	MPASS(*(MP)->mnt_op->vfs_susp_clean != NULL); 			\
-	VFS_PROLOGUE(MP);						\
-	(*(MP)->mnt_op->vfs_susp_clean)(MP);				\
-	VFS_EPILOGUE(MP);						\
+	if (*(MP)->mnt_op->vfs_susp_clean != NULL) {			\
+		VFS_PROLOGUE(MP);					\
+		(*(MP)->mnt_op->vfs_susp_clean)(MP);			\
+		VFS_EPILOGUE(MP);					\
+	}								\
 } while (0)
 
 #define	VFS_RECLAIM_LOWERVP(MP, VP) do {				\
diff --git a/sys/ufs/ffs/ffs_vfsops.c b/sys/ufs/ffs/ffs_vfsops.c
index d532e1b3..a047ef4 100644
--- a/sys/ufs/ffs/ffs_vfsops.c
+++ b/sys/ufs/ffs/ffs_vfsops.c
@@ -1055,7 +1055,7 @@ ffs_mountfs(devvp, mp, td)
 	 */
 	MNT_ILOCK(mp);
 	mp->mnt_kern_flag |= MNTK_LOOKUP_SHARED | MNTK_EXTENDED_SHARED |
-	    MNTK_NO_IOPF | MNTK_UNMAPPED_BUFS;
+	    MNTK_NO_IOPF | MNTK_UNMAPPED_BUFS | MNTK_SUSPENDABLE;
 	MNT_IUNLOCK(mp);
 #ifdef UFS_EXTATTR
 #ifdef UFS_EXTATTR_AUTOSTART