linux-kernel - Re: [PATCH v2] mm/memory-failure: fix deadlock when hugetlb_optimize

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Message-Id: <20240412162111.10f67ad0f001734464b53ad8@linux-foundation.org>
Date: Fri, 12 Apr 2024 16:21:11 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Miaohe Lin <linmiaohe@...wei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@...cle.com>, <naoya.horiguchi@....com>,
 <osalvador@...e.de>, <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mm/memory-failure: fix deadlock when
 hugetlb_optimize_vmemmap is enabled

On Fri, 12 Apr 2024 16:11:52 +0800 Miaohe Lin <linmiaohe@...wei.com> wrote:

> > I recently sent a patch[1] to convert dissolve_free_huge_page() to folios which changes the function name and the name referenced in the comment so this will conflict with my patch. It's in mm-unstable now, would you be able to rebase to that in a new version?
> > 

This patch is a hotfixes, cc:stable one so the mm-unstable material will be
based on top of this change.

I've queued this change up as a -fix against v1.  And I've retained
this changelog addition:

: This issue won't occur until commit a6b40850c442 ("mm: hugetlb: replace
: hugetlb_free_vmemmap_enabled with a static_key").  As it introduced
: rlock(cpu_hotplug_lock) in dissolve_free_huge_page() code path while
: lock(pcp_batch_high_lock) is already in the __page_handle_poison().

And I've queued another -fix to reflow that block comment to 80 columns.

--- a/mm/memory-failure.c~mm-memory-failure-fix-deadlock-when-hugetlb_optimize_vmemmap-is-enabled-v2-fix
+++ a/mm/memory-failure.c
@@ -155,14 +155,16 @@ static int __page_handle_poison(struct p
 	int ret;
 
 	/*
-	 * zone_pcp_disable() can't be used here. It will hold pcp_batch_high_lock and
-	 * dissolve_free_huge_page() might hold cpu_hotplug_lock via static_key_slow_dec()
-	 * when hugetlb vmemmap optimization is enabled. This will break current lock
-	 * dependency chain and leads to deadlock.
-	 * Disabling pcp before dissolving the page was a deterministic approach because
-	 * we made sure that those pages cannot end up in any PCP list. Draining PCP lists
-	 * expels those pages to the buddy system, but nothing guarantees that those pages
-	 * do not get back to a PCP queue if we need to refill those.
+	 * zone_pcp_disable() can't be used here. It will
+	 * hold pcp_batch_high_lock and dissolve_free_huge_page() might hold
+	 * cpu_hotplug_lock via static_key_slow_dec() when hugetlb vmemmap
+	 * optimization is enabled. This will break current lock dependency
+	 * chain and leads to deadlock.
+	 * Disabling pcp before dissolving the page was a deterministic
+	 * approach because we made sure that those pages cannot end up in any
+	 * PCP list. Draining PCP lists expels those pages to the buddy system,
+	 * but nothing guarantees that those pages do not get back to a PCP
+	 * queue if we need to refill those.
 	 */
 	ret = dissolve_free_huge_page(page);
 	if (!ret) {
_