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 <[email protected]>
Signed-off-by: Al Viro <[email protected]>

Documentation/filesystems/Locking

@@ -128,7 +128,7 @@ alloc_inode:
 destroy_inode:
 dirty_inode:				(must not sleep)
 write_inode:
-drop_inode:				!!!inode_lock!!!
+drop_inode:				!!!inode->i_lock!!!
 evict_inode:
 put_super:		write
 write_super:		read

Documentation/filesystems/porting

@@ -298,11 +298,14 @@ be used instead.  It gets called whenever the inode is evicted, whether it has
 remaining links or not.  Caller does *not* evict the pagecache or inode-associated
 metadata buffers; getting rid of those is responsibility of method, as it had
 been for ->delete_inode().
-	->drop_inode() returns int now; it's called on final iput() with inode_lock
-held and it returns true if filesystems wants the inode to be dropped.  As before,
-generic_drop_inode() is still the default and it's been updated appropriately.
-generic_delete_inode() is also alive and it consists simply of return 1.  Note that
-all actual eviction work is done by caller after ->drop_inode() returns.
+
+	->drop_inode() returns int now; it's called on final iput() with
+inode->i_lock held and it returns true if filesystems wants the inode to be
+dropped.  As before, generic_drop_inode() is still the default and it's been
+updated appropriately.  generic_delete_inode() is also alive and it consists
+simply of return 1.  Note that all actual eviction work is done by caller after
+->drop_inode() returns.
+
 	clear_inode() is gone; use end_writeback() instead.  As before, it must
 be called exactly once on each call of ->evict_inode() (as it used to be for
 each call of ->delete_inode()).  Unlike before, if you are using inode-associated
@@ -395,6 +398,9 @@ Currently you can only have FALLOC_FL_PUNCH_HOLE with FALLOC_FL_KEEP_SIZE set,
 so the i_size should not change when hole punching, even when puching the end of
 a file off.
 
+--
+[mandatory]
+
 --
 [mandatory]
 	->get_sb() is gone.  Switch to use of ->mount().  Typically it's just

Documentation/filesystems/vfs.txt

@@ -254,7 +254,7 @@ or bottom half).
 	should be synchronous or not, not all filesystems check this flag.
 
   drop_inode: called when the last access to the inode is dropped,
-	with the inode_lock spinlock held.
+	with the inode->i_lock spinlock held.
 
 	This method should be either NULL (normal UNIX filesystem
 	semantics) or "generic_delete_inode" (for filesystems that do not