[PATCH] NFS: only invalidate dentrys that are clearly invalid.

[NeilBrown]

Prior to commit 5ceb9d7fdaaf ("NFS: Refactor nfs_lookup_revalidate()")
and error from nfs_lookup_verify_inode() other than -ESTALE would result
in nfs_lookup_revalidate() returning that error code (-ESTALE is mapped
to zero).
Since that commit, all errors result in zero being returned.

When nfs_lookup_revalidate() returns zero, the dentry is invalidated
and, significantly, if the dentry is a directory that is mounted on,
that mountpoint is lost.

If you:
 - mount an NFS filesystem which contains a directory
 - mount something (e.g. tmpfs) on that directory
 - use iptables (or scissors) to block traffic to the server
 - ls -l the-mounted-on-directory
 - interrupt the 'ls -l'
you will find that the directory has been unmounted.

This can be fixed by returning the actual error code from
nfs_lookup_verify_inode() rather then zero (except for -ESTALE).

Fixes: 5ceb9d7fdaaf ("NFS: Refactor nfs_lookup_revalidate()")
Signed-off-by: NeilBrown <neilb@xxxxxxx>
---
 fs/nfs/dir.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index cb52db9a0cfb..d24acf556e9e 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1350,7 +1350,7 @@ nfs_do_lookup_revalidate(struct inode *dir, struct dentry *dentry,
 			 unsigned int flags)
 {
 	struct inode *inode;
-	int error;
+	int error = 0;
 
 	nfs_inc_stats(dir, NFSIOS_DENTRYREVALIDATE);
 	inode = d_inode(dentry);
@@ -1372,8 +1372,10 @@ nfs_do_lookup_revalidate(struct inode *dir, struct dentry *dentry,
 	    nfs_check_verifier(dir, dentry, flags & LOOKUP_RCU)) {
 		error = nfs_lookup_verify_inode(inode, flags);
 		if (error) {
-			if (error == -ESTALE)
+			if (error == -ESTALE) {
 				nfs_zap_caches(dir);
+				error = 0;
+			}
 			goto out_bad;
 		}
 		nfs_advise_use_readdirplus(dir);
@@ -1395,7 +1397,7 @@ nfs_do_lookup_revalidate(struct inode *dir, struct dentry *dentry,
 out_bad:
 	if (flags & LOOKUP_RCU)
 		return -ECHILD;
-	return nfs_lookup_revalidate_done(dir, dentry, inode, 0);
+	return nfs_lookup_revalidate_done(dir, dentry, inode, error);
 }
 
 static int
-- 
2.29.2

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