mm/hwpoison: decouple hwpoison_filter from mm/memory-failure.c

mm/memory-failure.c defines and uses hwpoison_filter_* parameters but the
values of those parameters can only be modified via mm/hwpoison-inject.c
from userspace.  They have a potentially different life time.  Decouple
those parameters from mm/memory-failure.c to fix this broken layering.

Link: https://lkml.kernel.org/r/20250904062258.3336092-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Suggested-by: Michal Hocko <mhocko@suse.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/proc/page.c

@@ -256,6 +256,7 @@ u64 stable_page_flags(const struct page *page)
 
 	return u;
 }
+EXPORT_SYMBOL_GPL(stable_page_flags);
 
 /* /proc/kpageflags - an array exposing page flags
  *

mm/hwpoison-inject.c

@@ -7,8 +7,96 @@
 #include <linux/swap.h>
 #include <linux/pagemap.h>
 #include <linux/hugetlb.h>
+#include <linux/page-flags.h>
+#include <linux/memcontrol.h>
 #include "internal.h"
 
+static u32 hwpoison_filter_enable;
+static u32 hwpoison_filter_dev_major = ~0U;
+static u32 hwpoison_filter_dev_minor = ~0U;
+static u64 hwpoison_filter_flags_mask;
+static u64 hwpoison_filter_flags_value;
+
+static int hwpoison_filter_dev(struct page *p)
+{
+	struct folio *folio = page_folio(p);
+	struct address_space *mapping;
+	dev_t dev;
+
+	if (hwpoison_filter_dev_major == ~0U &&
+	    hwpoison_filter_dev_minor == ~0U)
+		return 0;
+
+	mapping = folio_mapping(folio);
+	if (mapping == NULL || mapping->host == NULL)
+		return -EINVAL;
+
+	dev = mapping->host->i_sb->s_dev;
+	if (hwpoison_filter_dev_major != ~0U &&
+	    hwpoison_filter_dev_major != MAJOR(dev))
+		return -EINVAL;
+	if (hwpoison_filter_dev_minor != ~0U &&
+	    hwpoison_filter_dev_minor != MINOR(dev))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int hwpoison_filter_flags(struct page *p)
+{
+	if (!hwpoison_filter_flags_mask)
+		return 0;
+
+	if ((stable_page_flags(p) & hwpoison_filter_flags_mask) ==
+				    hwpoison_filter_flags_value)
+		return 0;
+	else
+		return -EINVAL;
+}
+
+/*
+ * This allows stress tests to limit test scope to a collection of tasks
+ * by putting them under some memcg. This prevents killing unrelated/important
+ * processes such as /sbin/init. Note that the target task may share clean
+ * pages with init (eg. libc text), which is harmless. If the target task
+ * share _dirty_ pages with another task B, the test scheme must make sure B
+ * is also included in the memcg. At last, due to race conditions this filter
+ * can only guarantee that the page either belongs to the memcg tasks, or is
+ * a freed page.
+ */
+#ifdef CONFIG_MEMCG
+static u64 hwpoison_filter_memcg;
+static int hwpoison_filter_task(struct page *p)
+{
+	if (!hwpoison_filter_memcg)
+		return 0;
+
+	if (page_cgroup_ino(p) != hwpoison_filter_memcg)
+		return -EINVAL;
+
+	return 0;
+}
+#else
+static int hwpoison_filter_task(struct page *p) { return 0; }
+#endif
+
+static int hwpoison_filter(struct page *p)
+{
+	if (!hwpoison_filter_enable)
+		return 0;
+
+	if (hwpoison_filter_dev(p))
+		return -EINVAL;
+
+	if (hwpoison_filter_flags(p))
+		return -EINVAL;
+
+	if (hwpoison_filter_task(p))
+		return -EINVAL;
+
+	return 0;
+}
+
 static struct dentry *hwpoison_dir;
 
 static int hwpoison_inject(void *data, u64 val)
@@ -67,6 +155,7 @@ DEFINE_DEBUGFS_ATTRIBUTE(unpoison_fops, NULL, hwpoison_unpoison, "%lli\n");
 static void __exit pfn_inject_exit(void)
 {
 	hwpoison_filter_enable = 0;
+	hwpoison_filter_unregister();
 	debugfs_remove_recursive(hwpoison_dir);
 }
 
@@ -105,6 +194,8 @@ static int __init pfn_inject_init(void)
 			   &hwpoison_filter_memcg);
 #endif
 
+	hwpoison_filter_register(hwpoison_filter);
+
 	return 0;
 }
 

mm/internal.h

@@ -1228,14 +1228,10 @@ static inline bool node_reclaim_enabled(void)
 #ifdef CONFIG_MEMORY_FAILURE
 int unmap_poisoned_folio(struct folio *folio, unsigned long pfn, bool must_kill);
 void shake_folio(struct folio *folio);
-extern int hwpoison_filter(struct page *p);
+typedef int hwpoison_filter_func_t(struct page *p);
+void hwpoison_filter_register(hwpoison_filter_func_t *filter);
+void hwpoison_filter_unregister(void);
 
-extern u32 hwpoison_filter_dev_major;
-extern u32 hwpoison_filter_dev_minor;
-extern u64 hwpoison_filter_flags_mask;
-extern u64 hwpoison_filter_flags_value;
-extern u64 hwpoison_filter_memcg;
-extern u32 hwpoison_filter_enable;
 #define MAGIC_HWPOISON	0x48575053U	/* HWPS */
 void SetPageHWPoisonTakenOff(struct page *page);
 void ClearPageHWPoisonTakenOff(struct page *page);

mm/memcontrol.c

@@ -287,6 +287,7 @@ ino_t page_cgroup_ino(struct page *page)
 	rcu_read_unlock();
 	return ino;
 }
+EXPORT_SYMBOL_GPL(page_cgroup_ino);
 
 /* Subset of node_stat_item for memcg stats */
 static const unsigned int memcg_node_stat_items[] = {

mm/memory-failure.c

@@ -212,106 +212,34 @@ static bool page_handle_poison(struct page *page, bool hugepage_or_freepage, boo
 	return true;
 }
 
-#if IS_ENABLED(CONFIG_HWPOISON_INJECT)
+static hwpoison_filter_func_t __rcu *hwpoison_filter_func __read_mostly;
 
-u32 hwpoison_filter_enable = 0;
-u32 hwpoison_filter_dev_major = ~0U;
-u32 hwpoison_filter_dev_minor = ~0U;
-u64 hwpoison_filter_flags_mask;
-u64 hwpoison_filter_flags_value;
-EXPORT_SYMBOL_GPL(hwpoison_filter_enable);
-EXPORT_SYMBOL_GPL(hwpoison_filter_dev_major);
-EXPORT_SYMBOL_GPL(hwpoison_filter_dev_minor);
-EXPORT_SYMBOL_GPL(hwpoison_filter_flags_mask);
-EXPORT_SYMBOL_GPL(hwpoison_filter_flags_value);
-
-static int hwpoison_filter_dev(struct page *p)
+void hwpoison_filter_register(hwpoison_filter_func_t *filter)
 {
-	struct folio *folio = page_folio(p);
-	struct address_space *mapping;
-	dev_t dev;
-
-	if (hwpoison_filter_dev_major == ~0U &&
-	    hwpoison_filter_dev_minor == ~0U)
-		return 0;
-
-	mapping = folio_mapping(folio);
-	if (mapping == NULL || mapping->host == NULL)
-		return -EINVAL;
-
-	dev = mapping->host->i_sb->s_dev;
-	if (hwpoison_filter_dev_major != ~0U &&
-	    hwpoison_filter_dev_major != MAJOR(dev))
-		return -EINVAL;
-	if (hwpoison_filter_dev_minor != ~0U &&
-	    hwpoison_filter_dev_minor != MINOR(dev))
-		return -EINVAL;
-
-	return 0;
+	rcu_assign_pointer(hwpoison_filter_func, filter);
 }
+EXPORT_SYMBOL_GPL(hwpoison_filter_register);
 
-static int hwpoison_filter_flags(struct page *p)
+void hwpoison_filter_unregister(void)
 {
-	if (!hwpoison_filter_flags_mask)
-		return 0;
-
-	if ((stable_page_flags(p) & hwpoison_filter_flags_mask) ==
-				    hwpoison_filter_flags_value)
-		return 0;
-	else
-		return -EINVAL;
+	RCU_INIT_POINTER(hwpoison_filter_func, NULL);
+	synchronize_rcu();
 }
+EXPORT_SYMBOL_GPL(hwpoison_filter_unregister);
 
-/*
- * This allows stress tests to limit test scope to a collection of tasks
- * by putting them under some memcg. This prevents killing unrelated/important
- * processes such as /sbin/init. Note that the target task may share clean
- * pages with init (eg. libc text), which is harmless. If the target task
- * share _dirty_ pages with another task B, the test scheme must make sure B
- * is also included in the memcg. At last, due to race conditions this filter
- * can only guarantee that the page either belongs to the memcg tasks, or is
- * a freed page.
- */
-#ifdef CONFIG_MEMCG
-u64 hwpoison_filter_memcg;
-EXPORT_SYMBOL_GPL(hwpoison_filter_memcg);
-static int hwpoison_filter_task(struct page *p)
+static int hwpoison_filter(struct page *p)
 {
-	if (!hwpoison_filter_memcg)
-		return 0;
+	int ret = 0;
+	hwpoison_filter_func_t *filter;
 
-	if (page_cgroup_ino(p) != hwpoison_filter_memcg)
-		return -EINVAL;
+	rcu_read_lock();
+	filter = rcu_dereference(hwpoison_filter_func);
+	if (filter)
+		ret = filter(p);
+	rcu_read_unlock();
 
-	return 0;
+	return ret;
 }
-#else
-static int hwpoison_filter_task(struct page *p) { return 0; }
-#endif
-
-int hwpoison_filter(struct page *p)
-{
-	if (!hwpoison_filter_enable)
-		return 0;
-
-	if (hwpoison_filter_dev(p))
-		return -EINVAL;
-
-	if (hwpoison_filter_flags(p))
-		return -EINVAL;
-
-	if (hwpoison_filter_task(p))
-		return -EINVAL;
-
-	return 0;
-}
-EXPORT_SYMBOL_GPL(hwpoison_filter);
-#else
-int hwpoison_filter(struct page *p)
-{
-	return 0;
-}
-#endif
 
 /*
  * Kill all processes that have a poisoned page mapped and then isolate