[PATCH v2 1/4] mm/hwpoison: mf_mutex for soft offline and unpoison

[Naoya Horiguchi <naoya.horiguchi@xxxxxxxxx>]

From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>

Originally mf_mutex is introduced to serialize multiple MCE events, but
it's also helpful to exclude races among  soft_offline_page() and
unpoison_memory().  So apply mf_mutex to them.

Signed-off-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
---
ChangeLog v2:
- add mutex_unlock() in "page already poisoned" path in soft_offline_page().
  (Thanks to Ding Hui)
---
 mm/memory-failure.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index fa9dda95a2a2..97297edfbd8e 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1628,6 +1628,8 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
 	return rc;
 }
 
+static DEFINE_MUTEX(mf_mutex);
+
 /**
  * memory_failure - Handle memory failure of a page.
  * @pfn: Page Number of the corrupted page
@@ -1654,7 +1656,6 @@ int memory_failure(unsigned long pfn, int flags)
 	int res = 0;
 	unsigned long page_flags;
 	bool retry = true;
-	static DEFINE_MUTEX(mf_mutex);
 
 	if (!sysctl_memory_failure_recovery)
 		panic("Memory failure on page %lx", pfn);
@@ -1978,6 +1979,7 @@ int unpoison_memory(unsigned long pfn)
 	struct page *page;
 	struct page *p;
 	int freeit = 0;
+	int ret = 0;
 	unsigned long flags = 0;
 	static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
 					DEFAULT_RATELIMIT_BURST);
@@ -1988,28 +1990,30 @@ int unpoison_memory(unsigned long pfn)
 	p = pfn_to_page(pfn);
 	page = compound_head(p);
 
+	mutex_lock(&mf_mutex);
+
 	if (!PageHWPoison(p)) {
 		unpoison_pr_info("Unpoison: Page was already unpoisoned %#lx\n",
 				 pfn, &unpoison_rs);
-		return 0;
+		goto unlock_mutex;
 	}
 
 	if (page_count(page) > 1) {
 		unpoison_pr_info("Unpoison: Someone grabs the hwpoison page %#lx\n",
 				 pfn, &unpoison_rs);
-		return 0;
+		goto unlock_mutex;
 	}
 
 	if (page_mapped(page)) {
 		unpoison_pr_info("Unpoison: Someone maps the hwpoison page %#lx\n",
 				 pfn, &unpoison_rs);
-		return 0;
+		goto unlock_mutex;
 	}
 
 	if (page_mapping(page)) {
 		unpoison_pr_info("Unpoison: the hwpoison page has non-NULL mapping %#lx\n",
 				 pfn, &unpoison_rs);
-		return 0;
+		goto unlock_mutex;
 	}
 
 	/*
@@ -2020,7 +2024,7 @@ int unpoison_memory(unsigned long pfn)
 	if (!PageHuge(page) && PageTransHuge(page)) {
 		unpoison_pr_info("Unpoison: Memory failure is now running on %#lx\n",
 				 pfn, &unpoison_rs);
-		return 0;
+		goto unlock_mutex;
 	}
 
 	if (!get_hwpoison_page(p, flags)) {
@@ -2028,7 +2032,7 @@ int unpoison_memory(unsigned long pfn)
 			num_poisoned_pages_dec();
 		unpoison_pr_info("Unpoison: Software-unpoisoned free page %#lx\n",
 				 pfn, &unpoison_rs);
-		return 0;
+		goto unlock_mutex;
 	}
 
 	lock_page(page);
@@ -2050,7 +2054,9 @@ int unpoison_memory(unsigned long pfn)
 	if (freeit && !(pfn == my_zero_pfn(0) && page_count(p) == 1))
 		put_page(page);
 
-	return 0;
+unlock_mutex:
+	mutex_unlock(&mf_mutex);
+	return ret;
 }
 EXPORT_SYMBOL(unpoison_memory);
 
@@ -2231,9 +2237,12 @@ int soft_offline_page(unsigned long pfn, int flags)
 		return -EIO;
 	}
 
+	mutex_lock(&mf_mutex);
+
 	if (PageHWPoison(page)) {
 		pr_info("%s: %#lx page already poisoned\n", __func__, pfn);
 		put_ref_page(ref_page);
+		mutex_unlock(&mf_mutex);
 		return 0;
 	}
 
@@ -2251,5 +2260,7 @@ int soft_offline_page(unsigned long pfn, int flags)
 		}
 	}
 
+	mutex_unlock(&mf_mutex);
+
 	return ret;
 }
-- 
2.25.1