[PATCH] Take i_mutex in splice_from_pipe()

The splice_actor may be calling ->prepare_write() and ->commit_write(). We
want i_mutex on the inode being written to before calling those so that we
don't race i_size changes.

The double locking behavior is done elsewhere in splice.c, and if we
eventually want _nolock variants of generic_file_splice_write(), fs modules
might have to replicate the nasty locking code. We introduce
inode_double_lock() and inode_double_unlock() to consolidate the locking
rules into one set of functions.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

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)
 {