locks: add a dedicated spinlock to protect i_flctx lists

We can now add a dedicated spinlock without expanding struct inode.
Change to using that to protect the various i_flctx lists.

Signed-off-by: Jeff Layton <jlayton@primarydata.com>
Acked-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index ea78f6f..b65166e 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1136,11 +1136,11 @@
 	if (!flctx)
 		goto out;
 
-	spin_lock(&inode->i_lock);
+	spin_lock(&flctx->flc_lock);
 	list_for_each(el, &flctx->flc_posix) {
 		count++;
 	}
-	spin_unlock(&inode->i_lock);
+	spin_unlock(&flctx->flc_lock);
 
 	INIT_LIST_HEAD(&locks_to_send);
 
@@ -1159,7 +1159,7 @@
 	}
 
 	el = locks_to_send.next;
-	spin_lock(&inode->i_lock);
+	spin_lock(&flctx->flc_lock);
 	list_for_each_entry(flock, &flctx->flc_posix, fl_list) {
 		if (el == &locks_to_send) {
 			/*
@@ -1181,7 +1181,7 @@
 		lck->type = type;
 		lck->offset = flock->fl_start;
 	}
-	spin_unlock(&inode->i_lock);
+	spin_unlock(&flctx->flc_lock);
 
 	list_for_each_entry_safe(lck, tmp, &locks_to_send, llist) {
 		int stored_rc;