Re: [PATCH 3/5] mm: Rework return value for copy_one_pte()

Oleg Nesterov
2020-09-22T16:54:11Z

On 09/22, Peter Xu wrote:
>
> On Tue, Sep 22, 2020 at 05:48:46PM +0200, Oleg Nesterov wrote:
> > > However since I didn't change this logic in this patch, it probably means this
> > > bug is also in the original code before this series... I'm thinking maybe I
> > > should prepare a standalone patch to clear the swp_entry_t and cc stable.
> >
> > Well, if copy_one_pte(src_pte) hits a swap entry and returns entry.val != 0, then
> > pte_none(*src_pte) is not possible after restart? This means that copy_one_pte()
> > will be called at least once.
>
> Note that we've released the page table locks, so afaict the old swp entry can
> be gone under us when we go back to the "do" loop... :)

But how?

I am just curious, I don't understand this code enough.

Oleg.