Rootfs mounted from user space - problem with umount

[John Zielinski <grim@undead.cc>]

I modified my kernel so that rootfs uses tmpfs (shm) instead of ramfs.  
I also modified it so that it allows mounting from user space.  My 
problem is when I try to umount it, umount hangs.  I checked it's 
proc/#/wchan entry and it's stuck in rwsem_down_write_failed.  Now the 
strange thing is I can mount it again from another console and then 
umount it with no problems.  It just hangs the first time.  I know I'm 
missing something simple but I can't seem to find it.

Here's the mods I made:

diff -urNX dontdiff linux.old/drivers/block/Kconfig linux/drivers/block/Kconfig
--- linux.old/drivers/block/Kconfig	2003-10-25 14:43:07.000000000 -0400
+++ linux/drivers/block/Kconfig	2003-11-28 23:43:05.000000000 -0500
@@ -320,6 +320,24 @@
 	  "real" root file system, etc. See <file:Documentation/initrd.txt>
 	  for details.
 
+config SHM_ROOTFS
+	bool "Use tmpfs (shm) instead of ramfs for rootfs"
+	depends on BLK_DEV_INITRD
+	default n
+	help
+	  This option switches rootfs so that it uses tmpfs rather than ramfs
+	  for it's file storage.  This makes rootfs swappable so having a large
+	  initrd or initramfs image won't eat up valuable RAM.
+	  
+	  You don't have to select the tmpfs option in the file system menu
+	  as that's only for user space mounting.  
+	  
+config RAMFS_ROOTFS
+	bool 
+	depends on !SHM_ROOTFS
+	default y
+	select RAMFS
+
 config LBD
 	bool "Support for Large Block Devices"
 	depends on X86 || MIPS32 || PPC32 || ARCH_S390_31 || SUPERH
diff -urNX dontdiff linux.old/fs/Kconfig linux/fs/Kconfig
--- linux.old/fs/Kconfig	2003-10-25 14:43:51.000000000 -0400
+++ linux/fs/Kconfig	2003-11-28 23:20:48.000000000 -0500
@@ -879,8 +879,8 @@
 config HUGETLB_PAGE
 	def_bool HUGETLBFS
 
-config RAMFS
-	bool
+config RAMFS 
+	tristate "Ramfs file system support"
 	default y
 	---help---
 	  Ramfs is a file system which keeps all files in RAM. It allows
diff -urNX dontdiff linux.old/fs/ramfs/inode.c linux/fs/ramfs/inode.c
--- linux.old/fs/ramfs/inode.c	2003-10-25 14:43:21.000000000 -0400
+++ linux/fs/ramfs/inode.c	2003-11-28 23:32:21.000000000 -0500
@@ -204,22 +204,26 @@
 	return get_sb_nodev(fs_type, flags, data, ramfs_fill_super);
 }
 
+#ifdef CONFIG_RAMFS_ROOTFS
 static struct super_block *rootfs_get_sb(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data)
 {
 	return get_sb_nodev(fs_type, flags|MS_NOUSER, data, ramfs_fill_super);
 }
+#endif
 
 static struct file_system_type ramfs_fs_type = {
 	.name		= "ramfs",
 	.get_sb		= ramfs_get_sb,
 	.kill_sb	= kill_litter_super,
 };
+#ifdef CONFIG_RAMFS_ROOTFS
 static struct file_system_type rootfs_fs_type = {
 	.name		= "rootfs",
 	.get_sb		= rootfs_get_sb,
 	.kill_sb	= kill_litter_super,
 };
+#endif
 
 static int __init init_ramfs_fs(void)
 {
@@ -234,9 +238,11 @@
 module_init(init_ramfs_fs)
 module_exit(exit_ramfs_fs)
 
+#ifdef CONFIG_RAMFS_ROOTFS
 int __init init_rootfs(void)
 {
 	return register_filesystem(&rootfs_fs_type);
 }
+#endif
 
 MODULE_LICENSE("GPL");
diff -urNX dontdiff linux.old/mm/shmem.c linux/mm/shmem.c
--- linux.old/mm/shmem.c	2003-10-25 14:43:30.000000000 -0400
+++ linux/mm/shmem.c	2003-11-29 00:00:37.000000000 -0500
@@ -1773,7 +1773,7 @@
 	sb->s_fs_info = NULL;
 }
 
-static kmem_cache_t *shmem_inode_cachep;
+static kmem_cache_t *shmem_inode_cachep = NULL;
 
 static struct inode *shmem_alloc_inode(struct super_block *sb)
 {
@@ -1801,12 +1801,14 @@
 
 static int init_inodecache(void)
 {
-	shmem_inode_cachep = kmem_cache_create("shmem_inode_cache",
-					     sizeof(struct shmem_inode_info),
-					     0, SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT,
-					     init_once, NULL);
-	if (shmem_inode_cachep == NULL)
-		return -ENOMEM;
+	if (!shmem_inode_cachep) {
+		shmem_inode_cachep = kmem_cache_create("shmem_inode_cache",
+						     sizeof(struct shmem_inode_info),
+						     0, SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT,
+						     init_once, NULL);
+		if (shmem_inode_cachep == NULL)
+			return -ENOMEM;
+	}
 	return 0;
 }
 
@@ -2008,3 +2010,29 @@
 }
 
 EXPORT_SYMBOL(shmem_file_setup);
+
+#ifdef CONFIG_SHM_ROOTFS
+static struct super_block *rootfs_sb = NULL;
+
+static struct super_block *rootfs_get_sb(struct file_system_type *fs_type,
+	int flags, const char *dev_name, void *data)
+{
+	if (!rootfs_sb) {
+		rootfs_sb = get_sb_single(fs_type, flags, data, shmem_fill_super);
+		shmem_set_size(SHMEM_SB(rootfs_sb), ULONG_MAX, ULONG_MAX);
+	}
+	return rootfs_sb;
+}
+
+static struct file_system_type rootfs_fs_type = {
+	.name		= "rootfs",
+	.get_sb		= rootfs_get_sb,
+	.kill_sb	= kill_litter_super,
+};
+
+int __init init_rootfs(void)
+{
+	init_inodecache();
+	return register_filesystem(&rootfs_fs_type);
+}
+#endif


John