Re: [PATCH v3 1/3] mm/swapfile: unuse_pte can map random data if swap read fails

[HORIGUCHI NAOYA(堀口 直也)]

On Sun, Apr 24, 2022 at 05:11:03PM +0800, Miaohe Lin wrote:
> There is a bug in unuse_pte(): when swap page happens to be unreadable,
> page filled with random data is mapped into user address space.  In case
> of error, a special swap entry indicating swap read fails is set to the
> page table.  So the swapcache page can be freed and the user won't end up
> with a permanently mounted swap because a sector is bad.  And if the page
> is accessed later, the user process will be killed so that corrupted data
> is never consumed.  On the other hand, if the page is never accessed, the
> user won't even notice it.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> Acked-by: David Hildenbrand <david@xxxxxxxxxx>

When I reproduced the issue (generated read error with dm-dust), I saw
infinite loop in the while loop in shmem_unuse_inode() (and this happens
even with this patch). I confirmed that shmem_swapin_page() returns -EIO,
but shmem_unuse_swap_entries() does not return the error to the callers,
so the while loop in shmem_unuse_inode() seems not break.

So maybe you need more code around shmem_unuse_inode() to handle the error?

Thanks,
Naoya Horiguchi