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

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@suse.de>
---
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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