Provide function to hold superblock reference when we are sure the
superblock is active. This function will get used by code reading
/proc/mounts and friends.
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/internal.h | 2 ++
fs/super.c | 35 +++++++++++++++++++++++++++++++++++
2 files changed, 37 insertions(+)
diff --git a/fs/internal.h b/fs/internal.h
index d410186bc369..c2c92be1e7df 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -104,6 +104,8 @@ extern bool trylock_super(struct super_block *sb);
extern struct dentry *mount_fs(struct file_system_type *,
int, const char *, void *);
extern struct super_block *user_get_super(dev_t);
+extern void hold_sb(struct super_block *sb);
+extern bool mount_trylock_super(struct super_block *sb);
/*
* open.c
diff --git a/fs/super.c b/fs/super.c
index ca53a08497ed..552d6247053b 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -775,6 +775,41 @@ struct super_block *get_super_exclusive_thawed(struct block_device *bdev)
}
EXPORT_SYMBOL(get_super_exclusive_thawed);
+/**
+ * hold_sb - get superblock reference for active superblock
+ * @sb: superblock to get reference for
+ *
+ * Get reference to superblock. The caller must make sure the superblock
+ * is currently active by other means (e.g. holding an active reference
+ * itself or holding namespace_sem preventing unmount).
+ */
+void hold_sb(struct super_block *sb)
+{
+ spin_lock(&sb_lock);
+ WARN_ON_ONCE(!atomic_read(&sb->s_active));
+ sb->s_count++;
+ spin_unlock(&sb_lock);
+}
+
+/**
+ * mount_trylock_super - get superblock and lock it against remount
+ * @sb: superblock to get reference for
+ *
+ * Get reference to superblock and protect superblock against racing
+ * remount or umount. The caller must make sure the superblock
+ * is currently active by other means (e.g. holding an active reference
+ * itself or holding namespace_sem preventing unmount).
+ */
+bool mount_trylock_super(struct super_block *sb)
+{
+ hold_sb(sb);
+ if (!down_read_trylock(&sb->s_umount)) {
+ put_super(sb);
+ return false;
+ }
+ return true;
+}
+
/**
* get_active_super - get an active reference to the superblock of a device
* @bdev: device to get the superblock for
--
2.16.4
