fs: remove inode_lock from iput_final and prune_icache

Now that inode state changes are protected by the inode->i_lock and
the inode LRU manipulations by the inode_lru_lock, we can remove the
inode_lock from prune_icache and the initial part of iput_final().

instead of using the inode_lock to protect the inode during
iput_final, use the inode->i_lock instead. This protects the inode
against new references being taken while we change the inode state
to I_FREEING, as well as preventing prune_icache from grabbing the
inode while we are manipulating it. Hence we no longer need the
inode_lock in iput_final prior to setting I_FREEING on the inode.

For prune_icache, we no longer need the inode_lock to protect the
LRU list, and the inodes themselves are protected against freeing
races by the inode->i_lock. Hence we can lift the inode_lock from
prune_icache as well.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/logfs/inode.c b/fs/logfs/inode.c
index 03b8c24..edfea7a 100644
--- a/fs/logfs/inode.c
+++ b/fs/logfs/inode.c
@@ -293,7 +293,7 @@
 	return ret;
 }
 
-/* called with inode_lock held */
+/* called with inode->i_lock held */
 static int logfs_drop_inode(struct inode *inode)
 {
 	struct logfs_super *super = logfs_super(inode->i_sb);