[PATCH] death of is_mounted() and aother fixes

*	new functions - bd_claim(bdev, holder) and bd_release(bdev).
	bd_claim(bdev, holder) fails is device is already claimed by
	somebody else; bd_release(bdev) gives device up.

*	get_sb_bdev() claims device for fs_type; it means that we don't need
	to look through entire least of superblocks anymore - just through
	the list of superblocks belonging to that type (i.e. the same thing
	we do for non-block filesystems; that will allow to merge quite a
	bit of code afterwards).

*	sys_swapon claims device for itself;  free exclusion with mounting,
	end of problems with bogus set_blocksize().

*	is_mounted() and is_swap_partition() are gone - what we actually
	wanted was "try to claim device for ourselves".  Which we can do
	now - without races inherent to is_mounted()/is_swap_partition().

*	RAID lock_rdev() claims device for itself.  I.e. we get rid of
	is_mounted() in there (BTW, is_swap_partition() was missing) and
	we get protection both ways - not only RAID won't take an already
	mounted device, but mount won't stomp on a device claimed by RAID.

There are other places that would benefit from the same (e.g. ext3 with
external journal almost definitely wants to claim device for itself).

Notice that it's a cooperative thing - neither open() nor raw device stuff
claim the block device, so they don't care if device is mounted, etc.  So
we don't break fsck and friends - exclusion is between those who know that
they want that exclusion.

drivers/block/blkpg.c

@@ -34,7 +34,6 @@
 #include <linux/blk.h>			/* for set_device_ro() */
 #include <linux/blkpg.h>
 #include <linux/genhd.h>
-#include <linux/swap.h>			/* for is_swap_partition() */
 #include <linux/module.h>               /* for EXPORT_SYMBOL */
 
 #include <asm/uaccess.h>
@@ -132,7 +131,9 @@ int del_partition(struct block_device *bdev, struct blkpg_partition *p)
 	kdev_t dev = to_kdev_t(bdev->bd_dev);
 	struct gendisk *g;
 	kdev_t devp;
+	struct block_device *bdevp;
 	int drive, first_minor, minor;
+	int holder;
 
 	/* find the drive major */
 	g = get_gendisk(dev);
@@ -155,17 +156,24 @@ int del_partition(struct block_device *bdev, struct blkpg_partition *p)
 
 	/* partition in use? Incomplete check for now. */
 	devp = mk_kdev(major(dev), minor);
-	if (is_mounted(devp) || is_swap_partition(devp))
+	bdevp = bdget(kdev_t_to_nr(devp));
+	if (!bdevp)
+		return -ENOMEM;
+	if (bd_claim(bdevp, &holder) < 0) {
+		bdput(bdevp);
 		return -EBUSY;
+	}
 
 	/* all seems OK */
-	fsync_dev(devp);
-	invalidate_buffers(devp);
+	fsync_bdev(bdevp);
+	invalidate_bdev(bdevp, 0);
 
 	g->part[minor].start_sect = 0;
 	g->part[minor].nr_sects = 0;
 	if (g->sizes)
 		g->sizes[minor] = 0;
+	bd_release(bdevp);
+	bdput(bdevp);
 
 	return 0;
 }
@@ -210,6 +218,7 @@ int blk_ioctl(struct block_device *bdev, unsigned int cmd, unsigned long arg)
 	int intval;
 	unsigned short usval;
 	kdev_t dev = to_kdev_t(bdev->bd_dev);
+	int holder;
 
 	intval = block_ioctl(dev, cmd, arg);
 	if (intval != -ENOTTY)
@@ -290,9 +299,10 @@ int blk_ioctl(struct block_device *bdev, unsigned int cmd, unsigned long arg)
 			if (intval > PAGE_SIZE || intval < 512 ||
 			    (intval & (intval - 1)))
 				return -EINVAL;
-			if (is_mounted(dev) || is_swap_partition(dev))
+			if (bd_claim(bdev, &holder) < 0)
 				return -EBUSY;
 			set_blocksize(dev, intval);
+			bd_release(bdev);
 			return 0;
 
 		default:

drivers/md/md.c

@@ -645,8 +645,14 @@ static int lock_rdev(mdk_rdev_t *rdev)
 	if (!bdev)
 		return -ENOMEM;
 	err = blkdev_get(bdev, FMODE_READ|FMODE_WRITE, 0, BDEV_RAW);
-	if (!err)
-		rdev->bdev = bdev;
+	if (err)
+		return err;
+	err = bd_claim(bdev, lock_rdev);
+	if (err) {
+		blkdev_put(bdev, BDEV_RAW);
+		return err;
+	}
+	rdev->bdev = bdev;
 	return err;
 }
 
@@ -656,6 +662,7 @@ static void unlock_rdev(mdk_rdev_t *rdev)
 	rdev->bdev = NULL;
 	if (!bdev)
 		MD_BUG();
+	bd_release(bdev);
 	blkdev_put(bdev, BDEV_RAW);
 }
 
@@ -1086,13 +1093,6 @@ static int md_import_device(kdev_t newdev, int on_disk)
 	}
 	memset(rdev, 0, sizeof(*rdev));
 
-	if (is_mounted(newdev)) {
-		printk(KERN_WARNING "md: can not import %s, has active inodes!\n",
-			partition_name(newdev));
-		err = -EBUSY;
-		goto abort_free;
-	}
-
 	if ((err = alloc_disk_sb(rdev)))
 		goto abort_free;
 

fs/block_dev.c

@@ -442,6 +442,27 @@ void bd_forget(struct inode *inode)
 	spin_unlock(&bdev_lock);
 }
 
+int bd_claim(struct block_device *bdev, void *holder)
+{
+	int res = -EBUSY;
+	spin_lock(&bdev_lock);
+	if (!bdev->bd_holder || bdev->bd_holder == holder) {
+		bdev->bd_holder = holder;
+		bdev->bd_holders++;
+		res = 0;
+	}
+	spin_unlock(&bdev_lock);
+	return res;
+}
+
+void bd_release(struct block_device *bdev)
+{
+	spin_lock(&bdev_lock);
+	if (!--bdev->bd_holders)
+		bdev->bd_holder = NULL;
+	spin_unlock(&bdev_lock);
+}
+
 static struct {
 	const char *name;
 	struct block_device_operations *bdops;

fs/super.c

@@ -444,9 +444,10 @@ static void shutdown_super(struct super_block *sb)
 	if (fs->fs_flags & FS_LITTER && sb->s_root)
 		d_genocide(sb->s_root);
 	generic_shutdown_super(sb);
-	if (bdev)
+	if (bdev) {
+		bd_release(bdev);
 		blkdev_put(bdev, BDEV_FS);
-	else
+	} else
 		put_anon_dev(dev);
 }
 
@@ -727,37 +728,40 @@ struct super_block *get_sb_bdev(struct file_system_type *fs_type,
 	error = -EACCES;
 	if (!(flags & MS_RDONLY) && is_read_only(dev))
 		goto out1;
+	error = bd_claim(bdev, fs_type);
+	if (error)
+		goto out1;
 
 	error = -ENOMEM;
 	s = alloc_super();
 	if (!s)
-		goto out1;
+		goto out2;
 
 	error = -EBUSY;
 restart:
 	spin_lock(&sb_lock);
 
-	list_for_each(p, &super_blocks) {
+	list_for_each(p, &fs_type->fs_supers) {
 		struct super_block *old = sb_entry(p);
 		if (old->s_bdev != bdev)
 			continue;
-		if (old->s_type != fs_type ||
-		    ((flags ^ old->s_flags) & MS_RDONLY)) {
-			spin_unlock(&sb_lock);
-			destroy_super(s);
-			goto out1;
-		}
 		if (!grab_super(old))
 			goto restart;
 		destroy_super(s);
+		if ((flags ^ old->s_flags) & MS_RDONLY) {
+			up_write(&old->s_umount);
+			kill_super(old);
+			old = ERR_PTR(-EBUSY);
+		}
+		bd_release(bdev);
 		blkdev_put(bdev, BDEV_FS);
 		path_release(&nd);
 		return old;
 	}
-	s->s_dev = dev;
 	s->s_bdev = bdev;
-	s->s_flags = flags;
+	s->s_dev = dev;
 	insert_super(s, fs_type);
+	s->s_flags = flags;
 	strncpy(s->s_id, bdevname(dev), sizeof(s->s_id));
 	error = fill_super(s, data, flags & MS_VERBOSE ? 1 : 0);
 	if (error)
@@ -770,6 +774,8 @@ struct super_block *get_sb_bdev(struct file_system_type *fs_type,
 	up_write(&s->s_umount);
 	kill_super(s);
 	goto out;
+out2:
+	bd_release(bdev);
 out1:
 	blkdev_put(bdev, BDEV_FS);
 out:

include/linux/fs.h

@@ -400,6 +400,8 @@ struct block_device {
 	const struct block_device_operations *bd_op;
 	struct semaphore	bd_sem;	/* open/close mutex */
 	struct list_head	bd_inodes;
+	void *			bd_holder;
+	int			bd_holders;
 };
 
 struct inode {
@@ -1069,6 +1071,8 @@ extern struct file_operations def_fifo_fops;
 extern int ioctl_by_bdev(struct block_device *, unsigned, unsigned long);
 extern int blkdev_get(struct block_device *, mode_t, unsigned, int);
 extern int blkdev_put(struct block_device *, int);
+extern int bd_claim(struct block_device *, void *);
+extern void bd_release(struct block_device *);
 
 /* fs/devices.c */
 extern const struct block_device_operations *get_blkfops(unsigned int);
@@ -1480,15 +1484,6 @@ extern int vfs_fstat(unsigned int, struct kstat *);
 extern struct file_system_type *get_fs_type(const char *name);
 extern struct super_block *get_super(kdev_t);
 extern void drop_super(struct super_block *sb);
-static inline int is_mounted(kdev_t dev)
-{
-	struct super_block *sb = get_super(dev);
-	if (sb) {
-		drop_super(sb);
-		return 1;
-	}
-	return 0;
-}
 extern kdev_t ROOT_DEV;
 extern char root_device_name[];
 

include/linux/swap.h

@@ -151,7 +151,6 @@ extern void out_of_memory(void);
 extern int total_swap_pages;
 extern unsigned int nr_swapfiles;
 extern struct swap_info_struct swap_info[];
-extern int is_swap_partition(kdev_t);
 extern void si_swapinfo(struct sysinfo *);
 extern swp_entry_t get_swap_page(void);
 extern void get_swaphandle_info(swp_entry_t, unsigned long *, struct inode **);

kernel/ksyms.c

@@ -198,6 +198,8 @@ EXPORT_SYMBOL(cdget);
 EXPORT_SYMBOL(cdput);
 EXPORT_SYMBOL(bdget);
 EXPORT_SYMBOL(bdput);
+EXPORT_SYMBOL(bd_claim);
+EXPORT_SYMBOL(bd_release);
 EXPORT_SYMBOL(__bread);
 EXPORT_SYMBOL(__brelse);
 EXPORT_SYMBOL(__bforget);

mm/swapfile.c

@@ -786,6 +786,8 @@ asmlinkage long sys_swapoff(const char * specialfile)
 	swap_device_unlock(p);
 	swap_list_unlock();
 	vfree(swap_map);
+	if (S_ISBLK(swap_file->f_dentry->d_inode->i_mode))
+		bd_release(swap_file->f_dentry->d_inode->i_bdev);
 	filp_close(swap_file, NULL);
 	err = 0;
 
@@ -833,19 +835,6 @@ int get_swaparea_info(char *buf)
 	return len;
 }
 
-int is_swap_partition(kdev_t dev) {
-	struct swap_info_struct *ptr = swap_info;
-	int i;
-
-	for (i = 0 ; i < nr_swapfiles ; i++, ptr++) {
-		if ((ptr->flags & SWP_USED) &&
-		    (ptr->flags & SWP_BLOCKDEV) &&
-		    (kdev_same(ptr->swap_file->f_dentry->d_inode->i_rdev, dev)))
-			return 1;
-	}
-	return 0;
-}
-
 /*
  * Written 01/25/92 by Simmule Turner, heavily changed by Linus.
  *
@@ -855,6 +844,7 @@ asmlinkage long sys_swapon(const char * specialfile, int swap_flags)
 {
 	struct swap_info_struct * p;
 	char *name;
+	struct block_device *bdev = NULL;
 	struct file *swap_file = NULL;
 	struct address_space *mapping;
 	unsigned int type;
@@ -905,13 +895,21 @@ asmlinkage long sys_swapon(const char * specialfile, int swap_flags)
 	swap_file = filp_open(name, O_RDWR, 0);
 	putname(name);
 	error = PTR_ERR(swap_file);
-	if (IS_ERR(swap_file))
+	if (IS_ERR(swap_file)) {
+		swap_file = NULL;
 		goto bad_swap_2;
+	}
 
 	p->swap_file = swap_file;
 
 	error = -EINVAL;
 	if (S_ISBLK(swap_file->f_dentry->d_inode->i_mode)) {
+		bdev = swap_file->f_dentry->d_inode->i_bdev;
+		error = bd_claim(bdev, sys_swapon);
+		if (error < 0) {
+			bdev = NULL;
+			goto bad_swap;
+		}
 		error = set_blocksize(swap_file->f_dentry->d_inode->i_rdev,
 				      PAGE_SIZE);
 		if (error < 0)
@@ -1066,6 +1064,8 @@ asmlinkage long sys_swapon(const char * specialfile, int swap_flags)
 	error = 0;
 	goto out;
 bad_swap:
+	if (bdev)
+		bd_release(bdev);
 bad_swap_2:
 	swap_list_lock();
 	swap_map = p->swap_map;