linux-kernel - Re: [PATCH v4 0/7] HWpoison: further fixes and cleanups

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Date:   Thu, 17 Sep 2020 15:09:52 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
Cc:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "aris@...vo.org" <aris@...vo.org>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "cai@....pw" <cai@....pw>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH v4 0/7] HWpoison: further fixes and cleanups

On Thu, Sep 17, 2020 at 11:39:21AM +0000, HORIGUCHI NAOYA(堀口 直也) wrote:
> Thanks for the update.
> This patchset triggers the following BUG_ON() with Aristeu's workload:

I just took a look, but I found more oddities.
The patchset you sent seems to be a bit buggy and it is missing some things
my patchset contains, e.g:

static __always_inline bool free_pages_prepare(struct page *page,
					unsigned int order, bool check_free)
{
	...
	if (unlikely(PageHWPoison(page)) && !order) {
	...
		return false;
}

Moreover, in page_handle_poison, you managed it wrong because:

static bool page_handle_poison(struct page *page, bool hugepage_or_freepage, bool release)
{
        if (release) {
                put_page(page);
                drain_all_pages(page_zone(page));
        }

	...
        SetPageHWPoison(page);
        page_ref_inc(page);

1) You are freeing the page first, which means it goes to buddy
2) Then you set it as poisoned and you update its refcount.

Now we have a page sitting in Buddy with a refcount = 1 and poisoned, and that is quite wrong.

Honestly, I do not know how your patchset diverged so much from mine, but is
not right.

I will go over my patchset and yours and compare/fix things.

-- 
Oscar Salvador
SUSE L3