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-rw-r--r--fs/inode.c36
1 files changed, 36 insertions, 0 deletions
diff --git a/fs/inode.c b/fs/inode.c
index d9a21d122926..26cdb115ce67 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1306,6 +1306,42 @@ void wake_up_inode(struct inode *inode)
wake_up_bit(&inode->i_state, __I_LOCK);
}
+/*
+ * We rarely want to lock two inodes that do not have a parent/child
+ * relationship (such as directory, child inode) simultaneously. The
+ * vast majority of file systems should be able to get along fine
+ * without this. Do not use these functions except as a last resort.
+ */
+void inode_double_lock(struct inode *inode1, struct inode *inode2)
+{
+ if (inode1 == NULL || inode2 == NULL || inode1 == inode2) {
+ if (inode1)
+ mutex_lock(&inode1->i_mutex);
+ else if (inode2)
+ mutex_lock(&inode2->i_mutex);
+ return;
+ }
+
+ if (inode1 < inode2) {
+ mutex_lock_nested(&inode1->i_mutex, I_MUTEX_PARENT);
+ mutex_lock_nested(&inode2->i_mutex, I_MUTEX_CHILD);
+ } else {
+ mutex_lock_nested(&inode2->i_mutex, I_MUTEX_PARENT);
+ mutex_lock_nested(&inode1->i_mutex, I_MUTEX_CHILD);
+ }
+}
+EXPORT_SYMBOL(inode_double_lock);
+
+void inode_double_unlock(struct inode *inode1, struct inode *inode2)
+{
+ if (inode1)
+ mutex_unlock(&inode1->i_mutex);
+
+ if (inode2 && inode2 != inode1)
+ mutex_unlock(&inode2->i_mutex);
+}
+EXPORT_SYMBOL(inode_double_unlock);
+
static __initdata unsigned long ihash_entries;
static int __init set_ihash_entries(char *str)
{