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Date:   Thu, 10 Jun 2021 16:50:59 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc:     linux-mm@kvack.org, Linus Torvalds <torvalds@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>,
        Michal Hocko <mhocko@suse.com>,
        Tony Luck <tony.luck@intel.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] mm/hwpoison: do not lock page again when
 me_huge_page() successfully recovers
Message-Id: <20210610165059.6618498250f60674c1bb9c03@linux-foundation.org>
In-Reply-To: <20210609072029.74645-1-nao.horiguchi@gmail.com>
References: <20210609072029.74645-1-nao.horiguchi@gmail.com>
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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?