linux-kernel - Re: [RFC PATCH 6/8] hugetlb: make free_huge

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Date:   Sun, 21 Mar 2021 12:55:25 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Michal Hocko <mhocko@...e.com>, Shakeel Butt <shakeelb@...gle.com>,
        Oscar Salvador <osalvador@...e.de>,
        David Hildenbrand <david@...hat.com>,
        Muchun Song <songmuchun@...edance.com>,
        David Rientjes <rientjes@...gle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        HORIGUCHI NAOYA <naoya.horiguchi@....com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Waiman Long <longman@...hat.com>, Peter Xu <peterx@...hat.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 6/8] hugetlb: make free_huge_page irq safe

On 3/19/21 3:42 PM, Mike Kravetz wrote:
> Commit c77c0a8ac4c5 ("mm/hugetlb: defer freeing of huge pages if in
> non-task context") was added to address the issue of free_huge_page
> being called from irq context.  That commit hands off free_huge_page
> processing to a workqueue if !in_task.  However, as seen in [1] this
> does not cover all cases.  Instead, make the locks taken in the
> free_huge_page irq safe.
> 
> This patch does the following:
> - Make hugetlb_lock irq safe.  This is mostly a simple process of
>   changing spin_*lock calls to spin_*lock_irq* calls.
> - Make subpool lock irq safe in a similar manner.
> - Revert the !in_task check and workqueue handoff.
> 
> [1] https://lore.kernel.org/linux-mm/000000000000f1c03b05bc43aadc@google.com/
> 
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> ---
>  mm/hugetlb.c        | 206 ++++++++++++++++++++------------------------
>  mm/hugetlb_cgroup.c |  10 ++-
>  2 files changed, 100 insertions(+), 116 deletions(-)

I missed the following changes:

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 5efff5ce337f..13d77d94d185 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2803,10 +2803,10 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 			break;
 
 		/* Drop lock as free routines may sleep */
-		spin_unlock(&hugetlb_lock);
+		spin_unlock_irqrestore(&hugetlb_lock, flags);
 		update_and_free_page(h, page);
 		cond_resched();
-		spin_lock(&hugetlb_lock);
+		spin_lock_irqsave(&hugetlb_lock, flags);
 
 		/* Recompute min_count in case hugetlb_lock was dropped */
 		min_count = min_hp_count(h, count);