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/super.c b/fs/nilfs2/super.c
index 1d1b6e1..f02762f 100644 (file)
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -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);
        }
 
        /*

diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 221953b..06e8dfd 100644 (file)
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -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;
 }

diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
index be4c040..d0cf4fb 100644 (file)
--- a/fs/nilfs2/the_nilfs.h
+++ b/fs/nilfs2/the_nilfs.h
@@ -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.