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From:   Michal Hocko <mhocko@kernel.org>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     David Hildenbrand <david@redhat.com>,
        Aili Yao <yaoaili@kingsoft.com>, <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Michal Hocko <mhocko@suse.com>
Subject: [PATCH] Revert "mm/gup: check page posion status for coredump."
Date:   Wed,  5 May 2021 15:54:07 +0200
Message-Id: <20210505135407.31590-1-mhocko@kernel.org>
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From: Michal Hocko <mhocko@suse.com>

While reviewing http://lkml.kernel.org/r/20210429122519.15183-4-david@redhat.com
I have crossed d3378e86d182 ("mm/gup: check page posion status for
coredump.") and noticed that this patch is broken in two ways. First it
doesn't really prevent hwpoison pages from being dumped because hwpoison
pages can be marked asynchornously at any time after the check.
Secondly, and more importantly, the patch introduces a ref count leak
because get_dump_page takes a reference on the page which is not
releases.

It also seems that the patch was merged incorrectly because there were
follow up changes not included as well as discussions on how to address
the underlying problem http://lkml.kernel.org/r/57ac524c-b49a-99ec-c1e4-ef5027bfb61b@redhat.com

Therefore revert the original patch.

Fixes: d3378e86d182 ("mm/gup: check page posion status for coredump.")
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 mm/gup.c      |  4 ----
 mm/internal.h | 20 --------------------
 2 files changed, 24 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 71e546e279fc..a33abe9048ed 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1592,10 +1592,6 @@ struct page *get_dump_page(unsigned long addr)
 				      FOLL_FORCE | FOLL_DUMP | FOLL_GET);
 	if (locked)
 		mmap_read_unlock(mm);
-
-	if (ret == 1 && is_page_poisoned(page))
-		return NULL;
-
 	return (ret == 1) ? page : NULL;
 }
 #endif /* CONFIG_ELF_CORE */
diff --git a/mm/internal.h b/mm/internal.h
index ef5f336f59bd..43c4a2f8d4cc 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -96,26 +96,6 @@ static inline void set_page_refcounted(struct page *page)
 	set_page_count(page, 1);
 }
 
-/*
- * When kernel touch the user page, the user page may be have been marked
- * poison but still mapped in user space, if without this page, the kernel
- * can guarantee the data integrity and operation success, the kernel is
- * better to check the posion status and avoid touching it, be good not to
- * panic, coredump for process fatal signal is a sample case matching this
- * scenario. Or if kernel can't guarantee the data integrity, it's better
- * not to call this function, let kernel touch the poison page and get to
- * panic.
- */
-static inline bool is_page_poisoned(struct page *page)
-{
-	if (PageHWPoison(page))
-		return true;
-	else if (PageHuge(page) && PageHWPoison(compound_head(page)))
-		return true;
-
-	return false;
-}
-
 extern unsigned long highest_memmap_pfn;
 
 /*
-- 
2.30.1