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

[Oscar Salvador]

On Sat, Feb 12, 2022 at 09:37:40PM -0500, Rik van Riel wrote:
> Sometimes the page offlining code can leave behind a hwpoisoned clean
> page cache page. 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.

Hi Rik,

Do you know how that exactly happens? We should not be really leaving
anything behind, and soft-offline (not hard) code works with the premise
of only poisoning a page in case it was contained, so I am wondering
what is going on here.

In-use pagecache pages are migrated away, and the actual page is
contained, and for clean ones, we already do the invalidate_inode_page()
and then contain it in case we succeed.

One scenario I can imagine this can happen is if by the time we call
page_handle_poison(), someone has taken another refcount on the page,
and the put_page() does not really free it, but I am not sure that
can happen.

-- 
Oscar Salvador
SUSE Labs