[PATCH v4 1/2] mm/memory-failure: introduce "hwpoisoned-pages" entry

[zhenwei pi <pizhenwei@bytedance.com>]

Add a new debug entry to show the number of hwpoisoned pages. And
use module_get/module_put to manager this kernel module, don't allow
to remove this module unless hwpoisoned-pages is zero.

Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
---
 Documentation/vm/hwpoison.rst |  4 ++++
 mm/hwpoison-inject.c          | 19 ++++++++++++++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/Documentation/vm/hwpoison.rst b/Documentation/vm/hwpoison.rst
index c742de1769d1..c832a8b192d4 100644
--- a/Documentation/vm/hwpoison.rst
+++ b/Documentation/vm/hwpoison.rst
@@ -155,6 +155,10 @@ Testing
 	flag bits are defined in include/linux/kernel-page-flags.h and
 	documented in Documentation/admin-guide/mm/pagemap.rst
 
+  hwpoisoned-pages
+	The number of hwpoisoned pages. The hwpoison kernel module can not be
+	removed unless this count is zero.
+
 * Architecture specific MCE injector
 
   x86 has mce-inject, mce-test
diff --git a/mm/hwpoison-inject.c b/mm/hwpoison-inject.c
index 5c0cddd81505..9e522ecedeef 100644
--- a/mm/hwpoison-inject.c
+++ b/mm/hwpoison-inject.c
@@ -10,6 +10,7 @@
 #include "internal.h"
 
 static struct dentry *hwpoison_dir;
+static atomic_t hwpoisoned_pages;
 
 static int hwpoison_inject(void *data, u64 val)
 {
@@ -49,15 +50,28 @@ static int hwpoison_inject(void *data, u64 val)
 inject:
 	pr_info("Injecting memory failure at pfn %#lx\n", pfn);
 	err = memory_failure(pfn, 0);
+	if (!err) {
+		WARN_ON(!try_module_get(THIS_MODULE));
+		atomic_inc(&hwpoisoned_pages);
+	}
+
 	return (err == -EOPNOTSUPP) ? 0 : err;
 }
 
 static int hwpoison_unpoison(void *data, u64 val)
 {
+	int ret;
+
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	return unpoison_memory(val);
+	ret = unpoison_memory(val);
+	if (!ret) {
+		atomic_dec(&hwpoisoned_pages);
+		module_put(THIS_MODULE);
+	}
+
+	return ret;
 }
 
 DEFINE_DEBUGFS_ATTRIBUTE(hwpoison_fops, NULL, hwpoison_inject, "%lli\n");
@@ -99,6 +113,9 @@ static int pfn_inject_init(void)
 	debugfs_create_u64("corrupt-filter-flags-value", 0600, hwpoison_dir,
 			   &hwpoison_filter_flags_value);
 
+	debugfs_create_atomic_t("hwpoisoned-pages", 0400, hwpoison_dir,
+			   &hwpoisoned_pages);
+
 #ifdef CONFIG_MEMCG
 	debugfs_create_u64("corrupt-filter-memcg", 0600, hwpoison_dir,
 			   &hwpoison_filter_memcg);
-- 
2.20.1