knfsd: nfsd4: don't delegate files that have had conflicts

One more incremental delegation policy improvement: don't give out a
delegation on a file if conflicting access has previously required that a
delegation be revoked on that file.  (In practice we'll forget about the
conflict when the struct nfs4_file is removed on close, so this is of limited
use for now, though it should at least solve a temporary problem with
self-conflicts on write opens from the same client.)
Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/nfsd/nfs4state.c

@@ -195,6 +195,8 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_stateid *stp, struct svc_f
 	struct nfs4_callback *cb = &stp->st_stateowner->so_client->cl_callback;
 
 	dprintk("NFSD alloc_init_deleg\n");
+	if (fp->fi_had_conflict)
+		return NULL;
 	if (num_delegations > max_delegations)
 		return NULL;
 	dp = kmem_cache_alloc(deleg_slab, GFP_KERNEL);
@@ -1002,6 +1004,7 @@ alloc_init_file(struct inode *ino)
 		list_add(&fp->fi_hash, &file_hashtbl[hashval]);
 		fp->fi_inode = igrab(ino);
 		fp->fi_id = current_fileid++;
+		fp->fi_had_conflict = false;
 		return fp;
 	}
 	return NULL;
@@ -1328,6 +1331,7 @@ do_recall(void *__dp)
 {
 	struct nfs4_delegation *dp = __dp;
 
+	dp->dl_file->fi_had_conflict = true;
 	nfsd4_cb_recall(dp);
 	return 0;
 }

include/linux/nfsd/state.h

@@ -224,6 +224,7 @@ struct nfs4_file {
 	struct inode		*fi_inode;
 	u32                     fi_id;      /* used with stateowner->so_id 
 					     * for stateid_hashtbl hash */
+	bool			fi_had_conflict;
 };
 
 /*