Re: [PATCH v3] mm/hwpoison: do not lock page again when me_huge_page() successfully recovers

[Andrew Morton <akpm@linux-foundation.org>]

On Wed,  9 Jun 2021 16:20:29 +0900 Naoya Horiguchi <nao.horiguchi@gmail.com> wrote:

> Currently me_huge_page() temporary unlocks page to perform some actions
> then locks it again later.  My testcase (which calls hard-offline on
> some tail page in a hugetlb, then accesses the address of the hugetlb
> range) showed that page allocation code detects this page lock on buddy
> page and printed out "BUG: Bad page state" message.
> 
> check_new_page_bad() does not consider a page with __PG_HWPOISON as bad
> page, so this flag works as kind of filter, but this filtering doesn't
> work in this case because the "bad page" is not the actual hwpoisoned
> page. So stop locking page again.  Actions to be taken depend on the
> page type of the error, so page unlocking should be done in ->action()
> callbacks.  So let's make it assumed and change all existing callbacks
> that way.

I'm getting a reject against Linus mainline here, and a -stable patch
doesn't want such things happening.

--- mm/memory-failure.c
+++ mm/memory-failure.c
@@ -1782,6 +1796,8 @@ int memory_failure(unsigned long pfn, int flags)
 
 identify_page_state:
 	res = identify_page_state(pfn, p, page_flags);
+	mutex_unlock(&mf_mutex);
+	return res;
 unlock_page:
 	unlock_page(p);
 unlock_mutex:

and...  That mutex_unlock() looks odd.  The patch adds no matching
mutex_lock?