fs: force_reval_path drop rcu-walk before d_invalidate

d_revalidate can return in rcu-walk mode even when it returns 0.  We can't just
call any old dcache function on rcu-walk dentry (the dentry is unstable, so
even through d_lock can safely be taken, the result may no longer be what we
expect -- careful re-checks would be required). So just drop rcu in this case.

(I missed this conversion when switching to the rcu-walk convention that Linus
suggested)

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

1 files changed, 10 insertions, 0 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 19433cdba011..0f02359ce685 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -583,6 +583,13 @@ void release_open_intent(struct nameidata *nd)
                 fput(nd->intent.open.file);
 }
 
+/*
+ * Call d_revalidate and handle filesystems that request rcu-walk
+ * to be dropped. This may be called and return in rcu-walk mode,
+ * regardless of success or error. If -ECHILD is returned, the caller
+ * must return -ECHILD back up the path walk stack so path walk may
+ * be restarted in ref-walk mode.
+ */
 static int d_revalidate(struct dentry *dentry, struct nameidata *nd)
 {
         int status;
@@ -673,6 +680,9 @@ force_reval_path(struct path *path, struct nameidata *nd)
                 return 0;
 
         if (!status) {
+                /* Don't d_invalidate in rcu-walk mode */
+                if (nameidata_drop_rcu(nd))
+                        return -ECHILD;
                 d_invalidate(dentry);
                 status = -ESTALE;
         }