mm/memory-failure: fix hardware poison check in unpoison_memory()

It was pointed out[1] that using folio_test_hwpoison() is wrong as we need
to check the indiviual page that has poison.  folio_test_hwpoison() only
checks the head page so go back to using PageHWPoison().

User-visible effects include existing hwpoison-inject tests possibly
failing as unpoisoning a single subpage could lead to unpoisoning an
entire folio.  Memory unpoisoning could also not work as expected as
the function will break early due to only checking the head page and
not the actually poisoned subpage.

[1]: https://lore.kernel.org/lkml/[email protected]/

Link: https://lkml.kernel.org/r/[email protected]
Fixes: a6fddef ("mm/memory-failure: convert unpoison_memory() to folios")
Signed-off-by: Sidhartha Kumar <[email protected]>
Reported-by: Matthew Wilcox (Oracle) <[email protected]>
Acked-by: Naoya Horiguchi <[email protected]>
Reviewed-by: Miaohe Lin <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/memory-failure.c

@@ -2487,7 +2487,7 @@ int unpoison_memory(unsigned long pfn)
 		goto unlock_mutex;
 	}
 
-	if (!folio_test_hwpoison(folio)) {
+	if (!PageHWPoison(p)) {
 		unpoison_pr_info("Unpoison: Page was already unpoisoned %#lx\n",
 				 pfn, &unpoison_rs);
 		goto unlock_mutex;