ceph: switch to vfs_inode_has_locks() to fix file lock bug

For the POSIX locks they are using the same owner, which is the
thread id. And multiple POSIX locks could be merged into single one,
so when checking whether the 'file' has locks may fail.

For a file where some openers use locking and others don't is a
really odd usage pattern though. Locks are like stoplights -- they
only work if everyone pays attention to them.

Just switch ceph_get_caps() to check whether any locks are set on
the inode. If there are POSIX/OFD/FLOCK locks on the file at the
time, we should set CHECK_FILELOCK, regardless of what fd was used
to set the lock.

Fixes: ff5d913d ("ceph: return -EIO if read/write against filp that lost file locks")
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/caps.c

@@ -2913,7 +2913,7 @@ int ceph_get_caps(struct file *filp, int need, int want, loff_t endoff, int *got
 
 	while (true) {
 		flags &= CEPH_FILE_MODE_MASK;
-		if (atomic_read(&fi->num_locks))
+		if (vfs_inode_has_locks(inode))
 			flags |= CHECK_FILELOCK;
 		_got = 0;
 		ret = try_get_cap_refs(inode, need, want, endoff,

fs/ceph/locks.c

@@ -32,18 +32,14 @@ void __init ceph_flock_init(void)
 
 static void ceph_fl_copy_lock(struct file_lock *dst, struct file_lock *src)
 {
-	struct ceph_file_info *fi = dst->fl_file->private_data;
 	struct inode *inode = file_inode(dst->fl_file);
 	atomic_inc(&ceph_inode(inode)->i_filelock_ref);
-	atomic_inc(&fi->num_locks);
 }
 
 static void ceph_fl_release_lock(struct file_lock *fl)
 {
-	struct ceph_file_info *fi = fl->fl_file->private_data;
 	struct inode *inode = file_inode(fl->fl_file);
 	struct ceph_inode_info *ci = ceph_inode(inode);
-	atomic_dec(&fi->num_locks);
 	if (atomic_dec_and_test(&ci->i_filelock_ref)) {
 		/* clear error when all locks are released */
 		spin_lock(&ci->i_ceph_lock);

fs/ceph/super.h

@@ -790,7 +790,6 @@ struct ceph_file_info {
 	struct list_head rw_contexts;
 
 	u32 filp_gen;
-	atomic_t num_locks;
 };
 
 struct ceph_dir_file_info {