From: Miklos Szeredi <mszeredi@redhat.com>
Date: Mon, 3 Nov 2025 13:10:38 +0000 (+0100)
Subject: fuse: add WARN_ON and comment for RCU revalidate
X-Git-Tag: v6.19-rc1~110^2~11
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=66c6a77e00a2f28330cca90c67339111cd54e54b;p=thirdparty%2Fkernel%2Flinux.git

fuse: add WARN_ON and comment for RCU revalidate

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 43ee4c7296a77..a153f449e2ad4 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -128,9 +128,17 @@ static int ovl_dentry_revalidate_common(struct dentry *dentry,
 	unsigned int i;
 	int ret = 1;
 
-	/* Careful in RCU mode */
-	if (!inode)
+	if (!inode) {
+		/*
+		 * Lookup of negative dentries will call ovl_dentry_init_flags()
+		 * with NULL upperdentry and NULL oe, resulting in the
+		 * DCACHE_OP*_REVALIDATE flags being cleared.  Hence the only
+		 * way to get a negative inode is due to a race with dentry
+		 * destruction.
+		 */
+		WARN_ON(!(flags & LOOKUP_RCU));
 		return -ECHILD;
+	}
 
 	oe = OVL_I_E(inode);
 	lowerstack = ovl_lowerstack(oe);