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.h b/fs/nilfs2/the_nilfs.h
index be4c040..d0cf4fb 100644
--- a/fs/nilfs2/the_nilfs.h
+++ b/fs/nilfs2/the_nilfs.h
@@ -48,6 +48,7 @@
* @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 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 @@
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.