queue-5.15/nfs-avoid-changing-nlink-when-file-removes-and-attri.patch

From b4810536792ab09ab8a44735a83ff54d6be0f4a1 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Mon, 17 Nov 2025 15:28:17 -0500
Subject: NFS: Avoid changing nlink when file removes and attribute updates
 race

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

[ Upstream commit bd4928ec799b31c492eb63f9f4a0c1e0bb4bb3f7 ]

If a file removal races with another operation that updates its
attributes, then skip the change to nlink, and just mark the attributes
as being stale.

Reported-by: Aiden Lambert <alambert48@gatech.edu>
Fixes: 59a707b0d42e ("NFS: Ensure we revalidate the inode correctly after remove or rename")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/nfs/dir.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 671b427b7b97a..2a325a79327bc 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1714,13 +1714,15 @@ static int nfs_dentry_delete(const struct dentry *dentry)
 }
 
 /* Ensure that we revalidate inode->i_nlink */
-static void nfs_drop_nlink(struct inode *inode)
+static void nfs_drop_nlink(struct inode *inode, unsigned long gencount)
 {
+	struct nfs_inode *nfsi = NFS_I(inode);
+
 	spin_lock(&inode->i_lock);
 	/* drop the inode if we're reasonably sure this is the last link */
-	if (inode->i_nlink > 0)
+	if (inode->i_nlink > 0 && gencount == nfsi->attr_gencount)
 		drop_nlink(inode);
-	NFS_I(inode)->attr_gencount = nfs_inc_attr_generation_counter();
+	nfsi->attr_gencount = nfs_inc_attr_generation_counter();
 	nfs_set_cache_invalid(
 		inode, NFS_INO_INVALID_CHANGE | NFS_INO_INVALID_CTIME |
 			       NFS_INO_INVALID_NLINK);
@@ -1738,8 +1740,9 @@ static void nfs_dentry_iput(struct dentry *dentry, struct inode *inode)
 		nfs_set_cache_invalid(inode, NFS_INO_INVALID_DATA);
 
 	if (dentry->d_flags & DCACHE_NFSFS_RENAMED) {
+		unsigned long gencount = READ_ONCE(NFS_I(inode)->attr_gencount);
 		nfs_complete_unlink(dentry, inode);
-		nfs_drop_nlink(inode);
+		nfs_drop_nlink(inode, gencount);
 	}
 	iput(inode);
 }
@@ -2281,9 +2284,11 @@ static int nfs_safe_remove(struct dentry *dentry)
 
 	trace_nfs_remove_enter(dir, dentry);
 	if (inode != NULL) {
+		unsigned long gencount = READ_ONCE(NFS_I(inode)->attr_gencount);
+
 		error = NFS_PROTO(dir)->remove(dir, dentry);
 		if (error == 0)
-			nfs_drop_nlink(inode);
+			nfs_drop_nlink(inode, gencount);
 	} else
 		error = NFS_PROTO(dir)->remove(dir, dentry);
 	if (error == -ENOENT)
@@ -2475,6 +2480,7 @@ int nfs_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
 {
 	struct inode *old_inode = d_inode(old_dentry);
 	struct inode *new_inode = d_inode(new_dentry);
+	unsigned long new_gencount = 0;
 	struct dentry *dentry = NULL;
 	struct rpc_task *task;
 	bool must_unblock = false;
@@ -2532,6 +2538,7 @@ int nfs_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
 		} else {
 			new_dentry->d_fsdata = NFS_FSDATA_BLOCKED;
 			must_unblock = true;
+			new_gencount = NFS_I(new_inode)->attr_gencount;
 			spin_unlock(&new_dentry->d_lock);
 		}
 
@@ -2568,7 +2575,7 @@ int nfs_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
 			new_dir, new_dentry, error);
 	if (!error) {
 		if (new_inode != NULL)
-			nfs_drop_nlink(new_inode);
+			nfs_drop_nlink(new_inode, new_gencount);
 		/*
 		 * The d_move() should be here instead of in an async RPC completion
 		 * handler because we need the proper locks to move the dentry.  If
-- 
2.51.0