[PATCH 4.9 196/240] NFS: Deal correctly with attribute generation counter overflow

Greg Kroah-Hartman
2021-05-20T11:21:13Z

From: Trond Myklebust <trond.myklebust@hammerspace.com>

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

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 6c0035761d17..7a94f5a5f8c8 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -1469,10 +1469,10 @@ 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)
@@ -1882,7 +1882,7 @@ 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;
}

--
2.30.2