linux-kernel - Re: [PATCH v4 4/8] hugetlb: create remove_hugetlb

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YGwwO0galuKQsD0J@dhcp22.suse.cz>
Date:   Tue, 6 Apr 2021 11:56:11 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Roman Gushchin <guro@...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>,
        Hillf Danton <hdanton@...a.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v4 4/8] hugetlb: create remove_hugetlb_page() to separate
 functionality

On Mon 05-04-21 16:00:39, Mike Kravetz wrote:
> The new remove_hugetlb_page() routine is designed to remove a hugetlb
> page from hugetlbfs processing.  It will remove the page from the active
> or free list, update global counters and set the compound page
> destructor to NULL so that PageHuge() will return false for the 'page'.
> After this call, the 'page' can be treated as a normal compound page or
> a collection of base size pages.
> 
> update_and_free_page no longer decrements h->nr_huge_pages{_node} as
> this is performed in remove_hugetlb_page.  The only functionality
> performed by update_and_free_page is to free the base pages to the lower
> level allocators.
> 
> update_and_free_page is typically called after remove_hugetlb_page.
> 
> remove_hugetlb_page is to be called with the hugetlb_lock held.
> 
> Creating this routine and separating functionality is in preparation for
> restructuring code to reduce lock hold times.  This commit should not
> introduce any changes to functionality.
> 
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>

Btw. I would prefer to reverse the ordering of this and Oscar's
patchset. This one is a bug fix which might be interesting for stable
backports while Oscar's work can be looked as a general functionality
improvement.

> @@ -2298,6 +2312,7 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
>  		/*
>  		 * Freed from under us. Drop new_page too.
>  		 */
> +		remove_hugetlb_page(h, new_page, false);
>  		update_and_free_page(h, new_page);
>  		goto unlock;
>  	} else if (page_count(old_page)) {
> @@ -2305,6 +2320,7 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
>  		 * Someone has grabbed the page, try to isolate it here.
>  		 * Fail with -EBUSY if not possible.
>  		 */
> +		remove_hugetlb_page(h, new_page, false);
>  		update_and_free_page(h, new_page);
>  		spin_unlock(&hugetlb_lock);
>  		if (!isolate_huge_page(old_page, list))

the page is not enqued anywhere here so remove_hugetlb_page would blow
when linked list debugging is enabled.
-- 
Michal Hocko
SUSE Labs