[1/2] vfs: Provide function to grab superblock reference
diff mbox series

Message ID 20181218134642.21219-2-jack@suse.cz
State New
Headers show
Series
  • vfs: Fix crashes when reading /proc/mounts
Related show

Commit Message

Jan Kara Dec. 18, 2018, 1:46 p.m. UTC
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@suse.cz>
---
 fs/internal.h |  2 ++
 fs/super.c    | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

Patch
diff mbox series

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