HWPOISON: Add unpoisoning support

The unpoisoning interface is useful for stress testing tools to
reclaim poisoned pages (to prevent OOM)

There is no hardware level unpoisioning, so this
cannot be used for real memory errors, only for software injected errors.

Note that it may leak pages silently - those who have been removed from
LRU cache, but not isolated from page cache/swap cache at hwpoison time.
Especially the stress test of dirty swap cache pages shall reboot system
before exhausting memory.

AK: Fix comments, add documentation, add printks, rename symbol

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

2 files changed, 2 insertions, 1 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 135e19198cd3..8cdb941fc7b5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1336,6 +1336,7 @@ enum mf_flags {
 };
 extern void memory_failure(unsigned long pfn, int trapno);
 extern int __memory_failure(unsigned long pfn, int trapno, int flags);
+extern int unpoison_memory(unsigned long pfn);
 extern int sysctl_memory_failure_early_kill;
 extern int sysctl_memory_failure_recovery;
 extern void shake_page(struct page *p);
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 49e907bd067f..f9df6308af95 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -275,7 +275,7 @@ PAGEFLAG_FALSE(Uncached)
 
 #ifdef CONFIG_MEMORY_FAILURE
 PAGEFLAG(HWPoison, hwpoison)
-TESTSETFLAG(HWPoison, hwpoison)
+TESTSCFLAG(HWPoison, hwpoison)
 #define __PG_HWPOISON (1UL << PG_hwpoison)
 #else
 PAGEFLAG_FALSE(HWPoison)