[1/2] vfs: Provide function to grab superblock reference
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Message ID 20181211172423.7709-2-jack@suse.cz
State New
Headers show
Series
  • vfs: Fix crashes when reading /proc/mounts
Related show

Commit Message

Jan Kara Dec. 11, 2018, 5:24 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 |  1 +
 fs/super.c    | 16 ++++++++++++++++
 2 files changed, 17 insertions(+)

Patch
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diff --git a/fs/internal.h b/fs/internal.h
index d410186bc369..608f4f276ba5 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -104,6 +104,7 @@  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);
 
 /*
  * open.c
diff --git a/fs/super.c b/fs/super.c
index ca53a08497ed..d34b8c49af9d 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -775,6 +775,22 @@  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);
+}
+
 /**
  * get_active_super - get an active reference to the superblock of a device
  * @bdev: device to get the superblock for