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

Hugh Dickins [off-list ref] writes:

On Tue, 3 Aug 2021, Matthew Wilcox wrote:

quoted

On Tue, Aug 03, 2021 at 04:14:38PM +0800, Huang, Ying wrote:

quoted

Matthew Wilcox [off-list ref] writes:

quoted

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?

I've been doing that swapon/swapoff loop for years, while running kernel
builds on tmpfs going out to swap; for better or worse on baremetal not VM.

You're right that few will ever need that level of reliability; but it
has caught problems from time to time, and I do insist on fixing them.

I'm not as insistent as you on wanting a reproducer; and we all take pride
sometimes in fixing ever more inconceivable bugs.  I'm not against that,
but it's easy to end up with a fix more dangerous than what it claims to
fix, rather like with random newbie cleanups.

Yes.  I totally agree, bug fixing is hard.

Best Regards,
Huang, Ying