NFS: Fix fcntl F_GETLK not reporting some conflicts

The commit 129a84de2347002f09721cda3155ccfd19fade40 (locks: fix F_GETLK
regression (failure to find conflicts)) fixed the posix_test_lock()
function by itself, however, its usage in NFS changed by the commit
9d6a8c5c213e34c475e72b245a8eb709258e968c (locks: give posix_test_lock
same interface as ->lock) remained broken - subsequent NFS-specific
locking code received F_UNLCK instead of the user-specified lock type.
To fix the problem, fl->fl_type needs to be saved before the
posix_test_lock() call and restored if no local conflicts were reported.

Reference: https://bugzilla.kernel.org/show_bug.cgi?id=23892
Tested-by: Alexander Morozov <amorozov@etersoft.ru>
Signed-off-by: Sergey Vlasov <vsu@altlinux.ru>
Cc: <stable@kernel.org>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/file.c

@@ -693,6 +693,7 @@ do_getlk(struct file *filp, int cmd, struct file_lock *fl, int is_local)
 {
 	struct inode *inode = filp->f_mapping->host;
 	int status = 0;
+	unsigned int saved_type = fl->fl_type;
 
 	/* Try local locking first */
 	posix_test_lock(filp, fl);
@@ -700,6 +701,7 @@ do_getlk(struct file *filp, int cmd, struct file_lock *fl, int is_local)
 		/* found a conflict */
 		goto out;
 	}
+	fl->fl_type = saved_type;
 
 	if (nfs_have_delegation(inode, FMODE_READ))
 		goto out_noconflict;