Re: [PATCH v2] mm: clean up hwpoison page cache page in fault path

[Rik van Riel <riel@surriel.com>]

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On Mon, 2022-02-14 at 15:24 -0800, Andrew Morton wrote:
> 
> > Subject: [PATCH v2] mm: clean up hwpoison page cache page in fault
> > path
> 
> At first scan I thought this was a code cleanup.
> 
> I think I'll do s/clean up/invalidate/.
> 
OK, that sounds good.

> On Sat, 12 Feb 2022 21:37:40 -0500 Rik van Riel <riel@surriel.com>
> wrote:
> 
> > Sometimes the page offlining code can leave behind a hwpoisoned
> > clean
> > page cache page.
> 
> Is this correct behaviour?

It is not desirable, and the soft page offlining code
tries to invalidate the page, but I don't think overhauling
the way we lock and refcount page cache pages just to make
offlining them more reliable would be worthwhile, when we
already have a branch in the page fault handler to deal with
these pages, anyway.

> > This can lead to programs being killed over and over
> > and over again as they fault in the hwpoisoned page, get killed,
> > and
> > then get re-spawned by whatever wanted to run them.
> > 
> > This is particularly embarrassing when the page was offlined due to
> > having too many corrected memory errors. Now we are killing tasks
> > due to them trying to access memory that probably isn't even
> > corrupted.
> > 
> > This problem can be avoided by invalidating the page from the page
> > fault handler, which already has a branch for dealing with these
> > kinds of pages. With this patch we simply pretend the page fault
> > was successful if the page was invalidated, return to userspace,
> > incur another page fault, read in the file from disk (to a new
> > memory page), and then everything works again.
> 
> Is this worth a cc:stable?

Maybe. I don't know how far back this issue goes...

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