linux-kernel - [PATCH v1 2/6] mm/hwpoison: remove race consideration

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Message-Id: <20210614021212.223326-3-nao.horiguchi@gmail.com>
Date:   Mon, 14 Jun 2021 11:12:08 +0900
From:   Naoya Horiguchi <nao.horiguchi@...il.com>
To:     linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        Ding Hui <dinghui@...gfor.com.cn>,
        Tony Luck <tony.luck@...el.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v1 2/6] mm/hwpoison: remove race consideration

From: Naoya Horiguchi <naoya.horiguchi@....com>

Now memory_failure() and unpoison_memory() are protected by mf_mutex,
so no need to explicitly check races between them.  So remove them.

Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
---
 mm/memory-failure.c | 37 -------------------------------------
 1 file changed, 37 deletions(-)

diff --git v5.13-rc5/mm/memory-failure.c v5.13-rc5_patched/mm/memory-failure.c
index 280eb6d6dd15..e7910386fc9c 100644
--- v5.13-rc5/mm/memory-failure.c
+++ v5.13-rc5_patched/mm/memory-failure.c
@@ -1461,14 +1461,6 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
 	lock_page(head);
 	page_flags = head->flags;
 
-	if (!PageHWPoison(head)) {
-		pr_err("Memory failure: %#lx: just unpoisoned\n", pfn);
-		num_poisoned_pages_dec();
-		unlock_page(head);
-		put_page(head);
-		return 0;
-	}
-
 	/*
 	 * TODO: hwpoison for pud-sized hugetlb doesn't work right now, so
 	 * simply disable it. In order to make it work properly, we need
@@ -1730,16 +1722,6 @@ int memory_failure(unsigned long pfn, int flags)
 	 */
 	page_flags = p->flags;
 
-	/*
-	 * unpoison always clear PG_hwpoison inside page lock
-	 */
-	if (!PageHWPoison(p)) {
-		pr_err("Memory failure: %#lx: just unpoisoned\n", pfn);
-		num_poisoned_pages_dec();
-		unlock_page(p);
-		put_page(p);
-		goto unlock_mutex;
-	}
 	if (hwpoison_filter(p)) {
 		if (TestClearPageHWPoison(p))
 			num_poisoned_pages_dec();
@@ -1956,17 +1938,6 @@ int unpoison_memory(unsigned long pfn)
 		goto unlock_mutex;
 	}
 
-	/*
-	 * unpoison_memory() can encounter thp only when the thp is being
-	 * worked by memory_failure() and the page lock is not held yet.
-	 * In such case, we yield to memory_failure() and make unpoison fail.
-	 */
-	if (!PageHuge(page) && PageTransHuge(page)) {
-		unpoison_pr_info("Unpoison: Memory failure is now running on %#lx\n",
-				 pfn, &unpoison_rs);
-		goto unlock_mutex;
-	}
-
 	if (!get_hwpoison_page(p, flags)) {
 		if (TestClearPageHWPoison(p))
 			num_poisoned_pages_dec();
@@ -1975,20 +1946,12 @@ int unpoison_memory(unsigned long pfn)
 		goto unlock_mutex;
 	}
 
-	lock_page(page);
-	/*
-	 * This test is racy because PG_hwpoison is set outside of page lock.
-	 * That's acceptable because that won't trigger kernel panic. Instead,
-	 * the PG_hwpoison page will be caught and isolated on the entrance to
-	 * the free buddy page pool.
-	 */
 	if (TestClearPageHWPoison(page)) {
 		unpoison_pr_info("Unpoison: Software-unpoisoned page %#lx\n",
 				 pfn, &unpoison_rs);
 		num_poisoned_pages_dec();
 		freeit = 1;
 	}
-	unlock_page(page);
 
 	put_page(page);
 	if (freeit && !(pfn == my_zero_pfn(0) && page_count(p) == 1))
-- 
2.25.1