From: Trond Myklebust <trond.myklebust@hammerspace.com>
Date: Mon, 29 Mar 2021 16:46:05 -0400
Subject: [PATCH] NFS: Deal correctly with attribute generation counter
 overflow
Git-commit: 9fdbfad1777cb4638f489eeb62d85432010c0031
Patch-mainline: v5.13
References: git-fixes

We need to use unsigned long subtraction and then convert to signed in
order to deal correcly with C overflow rules.

Fixes: f5062003465c ("NFS: Set an attribute barrier on all updates")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Acked-by: NeilBrown <neilb@suse.com>

---
 fs/nfs/inode.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -1506,10 +1506,10 @@ EXPORT_SYMBOL_GPL(_nfs_display_fhandle);
  */
 static int nfs_inode_attrs_need_update(const struct inode *inode, const struct nfs_fattr *fattr)
 {
-	const struct nfs_inode *nfsi = NFS_I(inode);
+	unsigned long attr_gencount = NFS_I(inode)->attr_gencount;
 
-	return ((long)fattr->gencount - (long)nfsi->attr_gencount) > 0 ||
-		((long)nfsi->attr_gencount - (long)nfs_read_attr_generation_counter() > 0);
+	return (long)(fattr->gencount - attr_gencount) > 0 ||
+	       (long)(attr_gencount - nfs_read_attr_generation_counter()) > 0;
 }
 
 static int nfs_refresh_inode_locked(struct inode *inode, struct nfs_fattr *fattr)
@@ -1912,7 +1912,7 @@ static int nfs_update_inode(struct inode
 			nfsi->attrtimeo_timestamp = now;
 		}
 		/* Set the barrier to be more recent than this fattr */
-		if ((long)fattr->gencount - (long)nfsi->attr_gencount > 0)
+		if ((long)(fattr->gencount - nfsi->attr_gencount) > 0)
 			nfsi->attr_gencount = fattr->gencount;
 	}