nfs_set_verifier() relies upon dentry being pinned; if that's
the case, grabbing ->d_lock stabilizes ->d_parent and guarantees
that ->d_parent points to a positive dentry. For something
we'd run into in RCU mode that is *not* true - dentry might've
been through dentry_kill() just as we grabbed ->d_lock, with
its parent going through the same just as we get to into
nfs_set_verifier_locked(). It might get to detaching inode
(and zeroing ->d_inode) before nfs_set_verifier_locked() gets
to fetching that; we get an oops as the result.
That can happen in nfs{,4} ->d_revalidate(); we check that
parent is positive, but that's done before we get to
nfs_set_verifier() and it's possible for memory pressure
to pick our dentry as eviction candidate by that time.
If that happens, back-to-back attempts to kill dentry and
its parent are quite normal.
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
fs/nfs/dir.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index e6a51fd94fea..8ffc1f78ba51 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1431,9 +1431,9 @@ static bool nfs_verifier_is_delegated(struct dentry *dentry)
static void nfs_set_verifier_locked(struct dentry *dentry, unsigned long verf)
{
struct inode *inode = d_inode(dentry);
- struct inode *dir = d_inode(dentry->d_parent);
+ struct inode *dir = d_inode_rcu(dentry->d_parent);
- if (!nfs_verify_change_attribute(dir, verf))
+ if (!dir || !nfs_verify_change_attribute(dir, verf))
return;
if (inode && NFS_PROTO(inode)->have_delegation(inode, FMODE_READ))
nfs_set_verifier_delegated(&verf);
--
2.39.2
