[PATCH v9 01/15] memory-failure: Fix hardware poison check in unpoison_memory() again

The earlier patch (6c54312f9689) that attempted to fix unpoison_memory()
was incorrect for hugetlb folios.  Before a6fddef49eef, we checked
the head page for poison (which was correct for hugetlb and incorrect
for THP).  We are currently incapable of unpoisoning pages (other than
the first page) in a hugetlb folio.

Use is_page_hwpoison() which handles hugetlb pages sufficiently well for
this purpose.  This is racy as we don't have a reference on the folio at
this point, but fixing that properly requires deeper surgery and this
is a CAP_SYS_ADMIN path only so this will do for the moment and can be
easily backported.  It's no worse than the situation before a6fddef49eef.

The other bug in a6fddef49eef is that we currently clear the HWPoison
flag on the precise page, which is wrong for hugetlb.  Fix that too.

Fixes: a6fddef49eef ("mm/memory-failure: convert unpoison_memory() to folios")
Cc: [email protected]
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Reviewed-by: Gregory Price (Meta) <[email protected]>
Reviewed-by: Miaohe Lin <[email protected]>
Reviewed-by: Jane Chu <[email protected]>
---
 mm/memory-failure.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 51508a55c405..944e6e1d4971 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2695,8 +2695,8 @@ int unpoison_memory(unsigned long pfn)
 		goto unlock_mutex;
 	}
 
-	if (!PageHWPoison(p)) {
-		unpoison_pr_info("%#lx: page was already unpoisoned\n",
+	if (!is_page_hwpoison(p)) {
+		unpoison_pr_info("%#lx: page is not poisoned\n",
 				 pfn, &unpoison_rs);
 		goto unlock_mutex;
 	}
@@ -2748,6 +2748,7 @@ int unpoison_memory(unsigned long pfn)
 				folio_put(folio);
 				goto unlock_mutex;
 			}
+			p = &folio->page;
 		}
 
 		folio_put(folio);
-- 
2.47.3