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: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 221953b..06e8dfd 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -72,6 +72,7 @@
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 *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 @@
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 @@
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 @@
ret++;
out_unlock:
- up_read(&nilfs->ns_sem);
+ up_read(&nilfs->ns_super_sem);
return ret;
}