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

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 12/15/2023 11:01 PM, Matthew Wilcox wrote:
> 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?

Yes, I think below check can avoid crash of dentry_name() used by '%pd'. 
Maybe we should also initialize on-stack dentry by
struct dentry dentry = { };

I can send a patch with your suggestion. Thanks.

> +++ 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;