NFS: Deal correctly with attribute generation counter overflow

[ Upstream commit 9fdbfad1777cb4638f489eeb62d85432010c0031 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 522aa10a1a3e7cfe64f07f79786c55bd6a35d84a..fd073b1caf6c8a14fc3969deb3a107c91b194ea2 100644 (file)
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -1635,10 +1635,10 @@ 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)
@@ -2067,7 +2067,7 @@ static int nfs_update_inode(struct inode *inode, struct nfs_fattr *fattr)
                        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;
        }