Commit 74dbbdd7 authored by Al Viro's avatar Al Viro
Browse files

New helper: deactivate_locked_super() 



Does equivalent of up_write(&s->s_umount); deactivate_super(s);
However, it does not does not unlock it until it's all over.
As the result, it's safe to use to dispose of new superblock on ->get_sb()
failure exits - nobody will see the sucker until it's all over.
Equivalent using up_write/deactivate_super is safe for that purpose
if superblock is either	safe to use or has NULL ->s_root when we unlock.
Normally filesystems take the required precautions, but
	a) we do have bugs in that area in some of them.
	b) up_write/deactivate_super sequence is extremely common,
so the helper makes sense anyway.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 677c9b2e

fs/super.c

+34 −12
Original line number Diff line number Diff line
@@ -207,6 +207,34 @@ void deactivate_super(struct super_block *s) 


EXPORT_SYMBOL(deactivate_super);



/**

 *	deactivate_locked_super	-	drop an active reference to superblock

 *	@s: superblock to deactivate

 *

 *	Equivalent of up_write(&s->s_umount); deactivate_super(s);, except that

 *	it does not unlock it until it's all over.  As the result, it's safe to

 *	use to dispose of new superblock on ->get_sb() failure exits - nobody

 *	will see the sucker until it's all over.  Equivalent using up_write +

 *	deactivate_super is safe for that purpose only if superblock is either

 *	safe to use or has NULL ->s_root when we unlock.

 */

void deactivate_locked_super(struct super_block *s)

{

	struct file_system_type *fs = s->s_type;

	if (atomic_dec_and_lock(&s->s_active, &sb_lock)) {

		s->s_count -= S_BIAS-1;

		spin_unlock(&sb_lock);

		vfs_dq_off(s, 0);

		fs->kill_sb(s);

		put_filesystem(fs);

		put_super(s);

	} else {

		up_write(&s->s_umount);

	}

}



EXPORT_SYMBOL(deactivate_locked_super);



/**

 *	grab_super - acquire an active reference

 *	@s: reference we are trying to make active
@@ -797,8 +825,7 @@ int get_sb_ns(struct file_system_type *fs_type, int flags, void *data, 
		sb->s_flags = flags;

		err = fill_super(sb, data, flags & MS_SILENT ? 1 : 0);

		if (err) {

			up_write(&sb->s_umount);

			deactivate_super(sb);

			deactivate_locked_super(sb);

			return err;

		}
@@ -854,8 +881,7 @@ int get_sb_bdev(struct file_system_type *fs_type, 


	if (s->s_root) {

		if ((flags ^ s->s_flags) & MS_RDONLY) {

			up_write(&s->s_umount);

			deactivate_super(s);

			deactivate_locked_super(s);

			error = -EBUSY;

			goto error_bdev;

		}
@@ -870,8 +896,7 @@ int get_sb_bdev(struct file_system_type *fs_type, 
		sb_set_blocksize(s, block_size(bdev));

		error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);

		if (error) {

			up_write(&s->s_umount);

			deactivate_super(s);

			deactivate_locked_super(s);

			goto error;

		}
@@ -921,8 +946,7 @@ int get_sb_nodev(struct file_system_type *fs_type, 


	error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);

	if (error) {

		up_write(&s->s_umount);

		deactivate_super(s);

		deactivate_locked_super(s);

		return error;

	}

	s->s_flags |= MS_ACTIVE;
@@ -952,8 +976,7 @@ int get_sb_single(struct file_system_type *fs_type, 
		s->s_flags = flags;

		error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);

		if (error) {

			up_write(&s->s_umount);

			deactivate_super(s);

			deactivate_locked_super(s);

			return error;

		}

		s->s_flags |= MS_ACTIVE;
@@ -1006,8 +1029,7 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void 
	return mnt;

out_sb:

	dput(mnt->mnt_root);

	up_write(&mnt->mnt_sb->s_umount);

	deactivate_super(mnt->mnt_sb);

	deactivate_locked_super(mnt->mnt_sb);

out_free_secdata:

	free_secdata(secdata);

out_mnt:

include/linux/fs.h

+1 −0
Original line number Diff line number Diff line
@@ -1775,6 +1775,7 @@ void kill_block_super(struct super_block *sb); 
void kill_anon_super(struct super_block *sb);

void kill_litter_super(struct super_block *sb);

void deactivate_super(struct super_block *sb);

void deactivate_locked_super(struct super_block *sb);

int set_anon_super(struct super_block *s, void *data);

struct super_block *sget(struct file_system_type *type,

			int (*test)(struct super_block *,void *),

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