NFSD: nfsd_file_put() can sleep

Now that there are no more callers of nfsd_file_put() that might
hold a spin lock, ensure the lockdep infrastructure can catch
newly introduced calls to nfsd_file_put() made while a spinlock
is held.

Link: https://lore.kernel.org/linux-nfs/ece7fd1d-5fb3-5155-54ba-347cfc19bd9a@oracle.com/T/#mf1855552570cf9a9c80d1e49d91438cd9085aada
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>

fs/nfsd/filecache.c

@@ -302,6 +302,8 @@ nfsd_file_put_noref(struct nfsd_file *nf)
 void
 nfsd_file_put(struct nfsd_file *nf)
 {
+	might_sleep();
+
 	set_bit(NFSD_FILE_REFERENCED, &nf->nf_flags);
 	if (test_bit(NFSD_FILE_HASHED, &nf->nf_flags) == 0) {
 		nfsd_file_flush(nf);