Re: [RFC PATCH v2 15/16] mm/hwpoison-inject: Rip off duplicated checks

From: Oscar Salvador
Date: Tue Oct 22 2019 - 03:57:51 EST

On Mon, Oct 21, 2019 at 11:40:39AM +0200, David Hildenbrand wrote:
> I explored somewhere already why this code was added:
> commit 31d3d3484f9bd263925ecaa341500ac2df3a5d9b
> Author: Wu Fengguang <fengguang.wu@xxxxxxxxx>
> Date: Wed Dec 16 12:19:59 2009 +0100
> HWPOISON: limit hwpoison injector to known page types
> __memory_failure()'s workflow is
> set PG_hwpoison
> //...
> unset PG_hwpoison if didn't pass hwpoison filter
> That could kill unrelated process if it happens to page fault on the
> page with the (temporary) PG_hwpoison. The race should be big enough to
> appear in stress tests.
> Fix it by grabbing the page and checking filter at inject time. This
> also avoids the very noisy "Injecting memory failure..." messages.
> - we don't touch madvise() based injection, because the filters are
> generally not necessary for it.
> - if we want to apply the filters to h/w aided injection, we'd better to
> rearrange the logic in __memory_failure() instead of this patch.
> AK: fix documentation, use drain all, cleanups
> You should justify why it is okay to do rip that code out now.
> It's not just duplicate checks.
> Was the documented race fixed?
> Will we fix the race within memory_failure() later?
> Don't we care?
> Also, you should add that this fixes the access of uninitialized memmaps
> now and makes the interface work correctly with devmem.

Thanks for bringuing this up David.
I guess I was carried away.

Since I have to do another re-spin to re-work a couple of things, I will
work on this as well.

Oscar Salvador