UBIFS: allow for racing between GC and TNC

The TNC mutex is unlocked prematurely when reading leaf nodes
with non-hashed keys.  This is unsafe because the node may be
moved by garbage collection and the eraseblock unmapped, although
that has never actually happened during stress testing.

This patch fixes the flaw by detecting the race and retrying with
the TNC mutex locked.

Signed-off-by: Adrian Hunter <ext-adrian.hunter@nokia.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/fs/ubifs/misc.h b/fs/ubifs/misc.h
index 87dabf9..87ced4c 100644
--- a/fs/ubifs/misc.h
+++ b/fs/ubifs/misc.h
@@ -325,4 +325,21 @@ static inline struct timespec ubifs_current_time(struct inode *inode)
 		current_fs_time(inode->i_sb) : CURRENT_TIME_SEC;
 }
 
+/**
+ * ubifs_tnc_lookup - look up a file-system node.
+ * @c: UBIFS file-system description object
+ * @key: node key to lookup
+ * @node: the node is returned here
+ *
+ * This function look up and reads node with key @key. The caller has to make
+ * sure the @node buffer is large enough to fit the node. Returns zero in case
+ * of success, %-ENOENT if the node was not found, and a negative error code in
+ * case of failure.
+ */
+static inline int ubifs_tnc_lookup(struct ubifs_info *c,
+				   const union ubifs_key *key, void *node)
+{
+	return ubifs_tnc_locate(c, key, node, NULL, NULL);
+}
+
 #endif /* __UBIFS_MISC_H__ */