Re: [PATCH] mm: migrate: fix getting incorrect page mapping during page migration

[Matthew Wilcox <willy@infradead.org>]

On Fri, Dec 15, 2023 at 02:51:43PM +0000, Matthew Wilcox wrote:
> I'm not saying no to this fix, but dump_mapping() is supposed to be
> resilient against this.  Is the issue that 'dentry' is NULL, or is it
> some field within dentry that is NULL?  eg, would this fix your
> case?

Uh, dentry is an on-stack dentry.  So obviously it's a pointer within it
that's NULL.  Maybe this, having stared at the implementation of %pd?

+++ b/fs/inode.c
@@ -588,7 +588,8 @@ void dump_mapping(const struct address_space *mapping)
        }

        dentry_ptr = container_of(dentry_first, struct dentry, d_u.d_alias);
-       if (get_kernel_nofault(dentry, dentry_ptr)) {
+       if (get_kernel_nofault(dentry, dentry_ptr) ||
+           !dentry->d_parent || !dentry->d_name) {
                pr_warn("aops:%ps ino:%lx invalid dentry:%px\n",
                                a_ops, ino, dentry_ptr);
                return;