Commit e59399d0 authored by Ryusuke Konishi's avatar Ryusuke Konishi Committed by Al Viro
Browse files

nilfs2: correct exclusion control in nilfs_remount function 



nilfs_remount() changes mount state of a superblock instance.  Even
though nilfs accesses other superblock instances during mount or
remount, the mount state was not properly protected in
nilfs_remount().

Moreover, nilfs_remount() has a lock order reversal problem;
nilfs_get_sb() holds:

  1. bdev->bd_mount_sem
  2. sb->s_umount  (sget acquires)

and nilfs_remount() holds:

  1. sb->s_umount  (locked by the caller in vfs)
  2. bdev->bd_mount_sem

To avoid these problems, this patch divides a semaphore protecting
super block instances from nilfs->ns_sem, and applies it to the mount
state protection in nilfs_remount().

With this change, bd_mount_sem use is removed from nilfs_remount() and
the lock order reversal will be resolved.  And the new rw-semaphore,
nilfs->ns_super_sem will properly protect the mount state except the
modification from nilfs_error function.

Signed-off-by: default avatarRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 6dd47406

fs/nilfs2/super.c

+20 −24
Original line number Diff line number Diff line
@@ -327,10 +327,10 @@ static void nilfs_put_super(struct super_block *sb) 
		nilfs_commit_super(sbi, 1);

		up_write(&nilfs->ns_sem);

	}

	down_write(&nilfs->ns_sem);

	down_write(&nilfs->ns_super_sem);

	if (nilfs->ns_current == sbi)

		nilfs->ns_current = NULL;

	up_write(&nilfs->ns_sem);

	up_write(&nilfs->ns_super_sem);



	nilfs_detach_checkpoint(sbi);

	put_nilfs(sbi->s_nilfs);
@@ -408,9 +408,9 @@ int nilfs_attach_checkpoint(struct nilfs_sb_info *sbi, __u64 cno) 
	struct buffer_head *bh_cp;

	int err;



	down_write(&nilfs->ns_sem);

	down_write(&nilfs->ns_super_sem);

	list_add(&sbi->s_list, &nilfs->ns_supers);

	up_write(&nilfs->ns_sem);

	up_write(&nilfs->ns_super_sem);



	sbi->s_ifile = nilfs_mdt_new(

		nilfs, sbi->s_super, NILFS_IFILE_INO, NILFS_IFILE_GFP);
@@ -448,9 +448,9 @@ int nilfs_attach_checkpoint(struct nilfs_sb_info *sbi, __u64 cno) 
	nilfs_mdt_destroy(sbi->s_ifile);

	sbi->s_ifile = NULL;



	down_write(&nilfs->ns_sem);

	down_write(&nilfs->ns_super_sem);

	list_del_init(&sbi->s_list);

	up_write(&nilfs->ns_sem);

	up_write(&nilfs->ns_super_sem);



	return err;

}
@@ -462,9 +462,9 @@ void nilfs_detach_checkpoint(struct nilfs_sb_info *sbi) 
	nilfs_mdt_clear(sbi->s_ifile);

	nilfs_mdt_destroy(sbi->s_ifile);

	sbi->s_ifile = NULL;

	down_write(&nilfs->ns_sem);

	down_write(&nilfs->ns_super_sem);

	list_del_init(&sbi->s_list);

	up_write(&nilfs->ns_sem);

	up_write(&nilfs->ns_super_sem);

}



static int nilfs_mark_recovery_complete(struct nilfs_sb_info *sbi)
@@ -883,10 +883,10 @@ nilfs_fill_super(struct super_block *sb, void *data, int silent, 
		goto failed_root;

	}



	down_write(&nilfs->ns_sem);

	down_write(&nilfs->ns_super_sem);

	if (!nilfs_test_opt(sbi, SNAPSHOT))

		nilfs->ns_current = sbi;

	up_write(&nilfs->ns_sem);

	up_write(&nilfs->ns_super_sem);



	return 0;
@@ -918,6 +918,7 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data) 


	lock_kernel();



	down_write(&nilfs->ns_super_sem);

	old_sb_flags = sb->s_flags;

	old_opts.mount_opt = sbi->s_mount_opt;

	old_opts.snapshot_cno = sbi->s_snapshot_cno;
@@ -965,24 +966,20 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data) 
		 * store the current valid flag.  (It may have been changed

		 * by fsck since we originally mounted the partition.)

		 */

		down(&sb->s_bdev->bd_mount_sem);

		down_read(&nilfs->ns_sem);

		if (nilfs->ns_current && nilfs->ns_current != sbi) {

			printk(KERN_WARNING "NILFS (device %s): couldn't "

			       "remount because an RW-mount exists.\n",

			       sb->s_id);

			up_read(&nilfs->ns_sem);

			err = -EBUSY;

			goto rw_remount_failed;

			goto restore_opts;

		}

		up_read(&nilfs->ns_sem);

		if (sbi->s_snapshot_cno != nilfs_last_cno(nilfs)) {

			printk(KERN_WARNING "NILFS (device %s): couldn't "

			       "remount because the current RO-mount is not "

			       "the latest one.\n",

			       sb->s_id);

			err = -EINVAL;

			goto rw_remount_failed;

			goto restore_opts;

		}

		sb->s_flags &= ~MS_RDONLY;

		nilfs_clear_opt(sbi, SNAPSHOT);
@@ -990,25 +987,24 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data) 


		err = nilfs_attach_segment_constructor(sbi);

		if (err)

			goto rw_remount_failed;

			goto restore_opts;



		down_write(&nilfs->ns_sem);

		nilfs_setup_super(sbi);

		nilfs->ns_current = sbi;

		up_write(&nilfs->ns_sem);



		up(&sb->s_bdev->bd_mount_sem);

		nilfs->ns_current = sbi;

	}

 out:

	up_write(&nilfs->ns_super_sem);

	unlock_kernel();

	return 0;



 rw_remount_failed:

	up(&sb->s_bdev->bd_mount_sem);

 restore_opts:

	sb->s_flags = old_sb_flags;

	sbi->s_mount_opt = old_opts.mount_opt;

	sbi->s_snapshot_cno = old_opts.snapshot_cno;

	up_write(&nilfs->ns_super_sem);

	unlock_kernel();

	return err;

}
@@ -1118,15 +1114,15 @@ nilfs_get_sb(struct file_system_type *fs_type, int flags, 
		 * (i.e. rw-mount or ro-mount), whereas rw-mount and

		 * ro-mount are mutually exclusive.

		 */

		down_read(&nilfs->ns_sem);

		down_read(&nilfs->ns_super_sem);

		if (nilfs->ns_current &&

		    ((nilfs->ns_current->s_super->s_flags ^ flags)

		     & MS_RDONLY)) {

			up_read(&nilfs->ns_sem);

			up_read(&nilfs->ns_super_sem);

			err = -EBUSY;

			goto failed_unlock;

		}

		up_read(&nilfs->ns_sem);

		up_read(&nilfs->ns_super_sem);

	}



	/*

fs/nilfs2/the_nilfs.c

+7 −6
Original line number Diff line number Diff line
@@ -72,6 +72,7 @@ static struct the_nilfs *alloc_nilfs(struct block_device *bdev) 
	atomic_set(&nilfs->ns_writer_refcount, -1);

	atomic_set(&nilfs->ns_ndirtyblks, 0);

	init_rwsem(&nilfs->ns_sem);

	init_rwsem(&nilfs->ns_super_sem);

	mutex_init(&nilfs->ns_writer_mutex);

	INIT_LIST_HEAD(&nilfs->ns_list);

	INIT_LIST_HEAD(&nilfs->ns_supers);
@@ -681,10 +682,10 @@ struct nilfs_sb_info *nilfs_find_sbinfo(struct the_nilfs *nilfs, 
{

	struct nilfs_sb_info *sbi;



	down_read(&nilfs->ns_sem);

	down_read(&nilfs->ns_super_sem);

	/*

	 * The SNAPSHOT flag and sb->s_flags are supposed to be

	 * protected with nilfs->ns_sem.

	 * protected with nilfs->ns_super_sem.

	 */

	sbi = nilfs->ns_current;

	if (rw_mount) {
@@ -705,12 +706,12 @@ struct nilfs_sb_info *nilfs_find_sbinfo(struct the_nilfs *nilfs, 
			goto found; /* snapshot mount */

	}

 out:

	up_read(&nilfs->ns_sem);

	up_read(&nilfs->ns_super_sem);

	return NULL;



 found:

	atomic_inc(&sbi->s_count);

	up_read(&nilfs->ns_sem);

	up_read(&nilfs->ns_super_sem);

	return sbi;

}
@@ -720,7 +721,7 @@ int nilfs_checkpoint_is_mounted(struct the_nilfs *nilfs, __u64 cno, 
	struct nilfs_sb_info *sbi;

	int ret = 0;



	down_read(&nilfs->ns_sem);

	down_read(&nilfs->ns_super_sem);

	if (cno == 0 || cno > nilfs->ns_cno)

		goto out_unlock;
@@ -737,6 +738,6 @@ int nilfs_checkpoint_is_mounted(struct the_nilfs *nilfs, __u64 cno, 
		ret++;



 out_unlock:

	up_read(&nilfs->ns_sem);

	up_read(&nilfs->ns_super_sem);

	return ret;

}

fs/nilfs2/the_nilfs.h

+6 −1
Original line number Diff line number Diff line
@@ -48,6 +48,7 @@ enum { 
 * @ns_bdi: backing dev info

 * @ns_writer: back pointer to writable nilfs_sb_info

 * @ns_sem: semaphore for shared states

 * @ns_super_sem: semaphore for global operations across super block instances

 * @ns_writer_mutex: mutex protecting ns_writer attach/detach

 * @ns_writer_refcount: number of referrers on ns_writer

 * @ns_current: back pointer to current mount
@@ -96,10 +97,15 @@ struct the_nilfs { 
	struct backing_dev_info *ns_bdi;

	struct nilfs_sb_info   *ns_writer;

	struct rw_semaphore	ns_sem;

	struct rw_semaphore	ns_super_sem;

	struct mutex		ns_writer_mutex;

	atomic_t		ns_writer_refcount;



	/*

	 * components protected by ns_super_sem

	 */

	struct nilfs_sb_info   *ns_current;

	struct list_head	ns_supers;



	/*

	 * used for
@@ -113,7 +119,6 @@ struct the_nilfs { 
	time_t			ns_sbwtime[2];

	unsigned		ns_sbsize;

	unsigned		ns_mount_state;

	struct list_head	ns_supers;



	/*

	 * Following fields are dedicated to a writable FS-instance.

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