Re: dio_get_page() lockdep complaints

[Zach Brown <zach.brown@oracle.com>]

> Without getting into a huge patch, the best fix would just be switching
> to try lock.  If the tail doesn't get packed, the world doesn't end.

So, something like this?

---

reiserfs: trylock i_mutex in file release when packing

The mmap_sem is nested under the i_mutex.  reiserfs_file_release() wants
to acquire the i_mutex to pack the file but it can be called with the mmap_sem
held by munmap.  This has produced lockdep warnings in testing.

  http://lkml.org/lkml/2007/4/19/73

This acquires the i_mutex in reiserfs_file_release() with a trylock.  If the
i_mutex is already held it simply won't pack.  There are already a host of
conditions under which it won't pack.

Totally untested, but built.

 Signed-off-by: Zach Brown <zach.brown@oracle.com>

diff --git a/fs/reiserfs/file.c b/fs/reiserfs/file.c
index a804903..40085f1 100644
--- a/fs/reiserfs/file.c
+++ b/fs/reiserfs/file.c
@@ -46,7 +46,13 @@ static int reiserfs_file_release(struct inode *inode, struct file *filp)
 		return 0;
 	}
 
-	mutex_lock(&inode->i_mutex);
+	/*
+	 * We can be called from munmap while holding mmap_sem, but mmap_sem
+	 * is nested inside i_mutex.  If we can't get i_mutex then we just
+	 * don't pack.
+	 */
+	if (mutex_trylock(&inode->i_mutex) == 0)
+		return 0;
 
 	mutex_lock(&(REISERFS_I(inode)->i_mmap));
 	if (REISERFS_I(inode)->i_flags & i_ever_mapped)