Re: [PATCH] mm,shmem: Fix a typo in shmem_swapin_page()

From: Matthew Wilcox
Date: Tue Aug 03 2021 - 08:02:27 EST

On Tue, Aug 03, 2021 at 04:14:38PM +0800, Huang, Ying wrote:
> Matthew Wilcox <willy@xxxxxxxxxxxxx> writes:
> > But I REALLY REALLY REALLY want a reproducer. Right now, I have a hard
> > time believing this, or any of the other races can really happen.
> I think the race is only theoretical too. Firstly, swapoff is a rare
> operations in practice; secondly, the race window is really small.

So do something to provoke it. Widen the window. Put an msleep(1000)
between *pagep = NULL and the call to get_swap_device(). That's assuming
that the swapon/swapoff loop that I proposed doesn't work. Did you
try it?