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nilfs2: correct exclusion control in nilfs_remount function

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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: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Ryusuke Konishi 2009-06-08 01:39:32 +09:00 committed by Al Viro
parent 6dd4740662
commit e59399d010
3 changed files with 33 additions and 31 deletions
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44
fs/nilfs2/super.c
View file

@ -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);
}
/*

13
fs/nilfs2/the_nilfs.c
View file

@ -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;
}

7
fs/nilfs2/the_nilfs.h
View file

@ -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.