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

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Date:   Thu, 17 Sep 2020 15:40:06 +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 03:09:52PM +0200, Oscar Salvador wrote:
> 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.

Hi Naoya,

Ok, I tested it and with the following changes on top I cannot reproduce the issue:

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index f68cb5e3b320..4ffaaa5c2603 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -67,11 +67,6 @@ atomic_long_t num_poisoned_pages __read_mostly = ATOMIC_LONG_INIT(0);
 
 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));
-	}
-
 	if (hugepage_or_freepage) {
 		/*
 		 * Doing this check for free pages is also fine since dissolve_free_huge_page
@@ -89,6 +84,12 @@ static bool page_handle_poison(struct page *page, bool hugepage_or_freepage, boo
 	}
 
 	SetPageHWPoison(page);
+
+	if (release) {
+                put_page(page);
+                drain_all_pages(page_zone(page));
+        }
+
 	page_ref_inc(page);
 	num_poisoned_pages_inc();
 	return true;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0d9f9bd0e06c..8a6ab05f074c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1173,6 +1173,16 @@ static __always_inline bool free_pages_prepare(struct page *page,
 
 	trace_mm_page_free(page, order);
 
+	if (unlikely(PageHWPoison(page)) && !order) {
+		/*
+		 * Untie memcg state and reset page's owner
+		 */
+		if (memcg_kmem_enabled() && PageKmemcg(page))
+			__memcg_kmem_uncharge_page(page, order);
+		reset_page_owner(page, order);
+		return false;
+	}
+
 	/*
 	 * Check tail pages before head page information is cleared to
 	 * avoid checking PageCompound for order-0 pages.


# sh tmp_run_ksm_madv.sh 
p1 0x7f6b6b08e000
p2 0x7f6b529ee000
madvise(p1) 0
madvise(p2) 0
writing p1 ... done
writing p2 ... done
soft offline
soft offline returns 0
OK


Can you try to re-run your tests and see if they come clean?
If they do, I will try to see if Andrew can squezee above changes into [1],
where they belong to.

Otherwise I will craft a v5 containing all fixups (pretty unfortunate).

[1] https://patchwork.kernel.org/patch/11704099/

-- 
Oscar Salvador
SUSE L3