NFS: Add deferred cache invalidation for close-to-open consistency violations

If the client detects that close-to-open cache consistency has been
violated, and that the file or directory has been changed on the
server, then do a cache invalidation when we're done working with
the file.
The reason we don't do an immediate cache invalidation is that we
want to avoid performance problems due to false positives. Also,
note that we cannot guarantee cache consistency in this situation
even if we do invalidate the cache.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/dir.c

@@ -80,6 +80,10 @@ static struct nfs_open_dir_context *alloc_nfs_open_dir_context(struct inode *dir
 		ctx->dup_cookie = 0;
 		ctx->cred = get_cred(cred);
 		spin_lock(&dir->i_lock);
+		if (list_empty(&nfsi->open_files) &&
+		    (nfsi->cache_validity & NFS_INO_DATA_INVAL_DEFER))
+			nfsi->cache_validity |= NFS_INO_INVALID_DATA |
+				NFS_INO_REVAL_FORCED;
 		list_add(&ctx->list, &nfsi->open_files);
 		spin_unlock(&dir->i_lock);
 		return ctx;

fs/nfs/inode.c

@@ -208,7 +208,7 @@ static void nfs_set_cache_invalid(struct inode *inode, unsigned long flags)
 	}
 
 	if (inode->i_mapping->nrpages == 0)
-		flags &= ~NFS_INO_INVALID_DATA;
+		flags &= ~(NFS_INO_INVALID_DATA|NFS_INO_DATA_INVAL_DEFER);
 	nfsi->cache_validity |= flags;
 	if (flags & NFS_INO_INVALID_DATA)
 		nfs_fscache_invalidate(inode);
@@ -652,7 +652,8 @@ static int nfs_vmtruncate(struct inode * inode, loff_t offset)
 	i_size_write(inode, offset);
 	/* Optimisation */
 	if (offset == 0)
-		NFS_I(inode)->cache_validity &= ~NFS_INO_INVALID_DATA;
+		NFS_I(inode)->cache_validity &= ~(NFS_INO_INVALID_DATA |
+				NFS_INO_DATA_INVAL_DEFER);
 	NFS_I(inode)->cache_validity &= ~NFS_INO_INVALID_SIZE;
 
 	spin_unlock(&inode->i_lock);
@@ -1032,6 +1033,10 @@ void nfs_inode_attach_open_context(struct nfs_open_context *ctx)
 	struct nfs_inode *nfsi = NFS_I(inode);
 
 	spin_lock(&inode->i_lock);
+	if (list_empty(&nfsi->open_files) &&
+	    (nfsi->cache_validity & NFS_INO_DATA_INVAL_DEFER))
+		nfsi->cache_validity |= NFS_INO_INVALID_DATA |
+			NFS_INO_REVAL_FORCED;
 	list_add_tail_rcu(&ctx->list, &nfsi->open_files);
 	spin_unlock(&inode->i_lock);
 }
@@ -1313,7 +1318,8 @@ int nfs_revalidate_mapping(struct inode *inode,
 
 	set_bit(NFS_INO_INVALIDATING, bitlock);
 	smp_wmb();
-	nfsi->cache_validity &= ~NFS_INO_INVALID_DATA;
+	nfsi->cache_validity &= ~(NFS_INO_INVALID_DATA|
+			NFS_INO_DATA_INVAL_DEFER);
 	spin_unlock(&inode->i_lock);
 	trace_nfs_invalidate_mapping_enter(inode);
 	ret = nfs_invalidate_mapping(inode, mapping);
@@ -1871,7 +1877,8 @@ static int nfs_update_inode(struct inode *inode, struct nfs_fattr *fattr)
 				dprintk("NFS: change_attr change on server for file %s/%ld\n",
 						inode->i_sb->s_id,
 						inode->i_ino);
-			}
+			} else if (!have_delegation)
+				nfsi->cache_validity |= NFS_INO_DATA_INVAL_DEFER;
 			inode_set_iversion_raw(inode, fattr->change_attr);
 			attr_changed = true;
 		}

include/linux/nfs_fs.h

@@ -223,6 +223,8 @@ struct nfs4_copy_state {
 #define NFS_INO_INVALID_MTIME	BIT(10)		/* cached mtime is invalid */
 #define NFS_INO_INVALID_SIZE	BIT(11)		/* cached size is invalid */
 #define NFS_INO_INVALID_OTHER	BIT(12)		/* other attrs are invalid */
+#define NFS_INO_DATA_INVAL_DEFER	\
+				BIT(13)		/* Deferred cache invalidation */
 
 #define NFS_INO_INVALID_ATTR	(NFS_INO_INVALID_CHANGE \
 		| NFS_INO_INVALID_CTIME \