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From: Yang Shi <shy828301@gmail.com>
To: Miaohe Lin <linmiaohe@huawei.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Jerome Glisse <jglisse@redhat.com>,
	 Rafael Aquini <aquini@redhat.com>,
	David Hildenbrand <david@redhat.com>,
	 Alistair Popple <apopple@nvidia.com>,
	 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux MM <linux-mm@kvack.org>
Subject: Re: [PATCH v2 5/5] mm/migrate.c: fix potential deadlock in NUMA balancing shared exec THP case
Date: Tue, 23 Mar 2021 18:16:10 -0700	[thread overview]
Message-ID: <CAHbLzko11ygmDp3pRry8meo3PhdXwro1rid-aBomC=0+rm3u6Q@mail.gmail.com> (raw)
In-Reply-To: <CAHbLzkoSsPWSdyZQBR03NbU8i3AG_DTL4P-efYULvuYmWzyYbg@mail.gmail.com>

On Tue, Mar 23, 2021 at 10:17 AM Yang Shi <shy828301@gmail.com> wrote:
>
> On Tue, Mar 23, 2021 at 6:55 AM Miaohe Lin <linmiaohe@huawei.com> wrote:
> >
> > Since commit c77c5cbafe54 ("mm: migrate: skip shared exec THP for NUMA
> > balancing"), the NUMA balancing would skip shared exec transhuge page.
> > But this enhancement is not suitable for transhuge page. Because it's
> > required that page_mapcount() must be 1 due to no migration pte dance
> > is done here. On the other hand, the shared exec transhuge page will
> > leave the migrate_misplaced_page() with pte entry untouched and page
> > locked. Thus pagefault for NUMA will be triggered again and deadlock
> > occurs when we start waiting for the page lock held by ourselves.
>
> Thanks for catching this. By relooking the code I think the other
> important reason for removing this is
> migrate_misplaced_transhuge_page() actually can't see shared exec file
> THP at all since page_lock_anon_vma_read() is called before and if
> page is not anonymous page it will just restore the PMD without
> migrating anything.
>
> The pages for private mapped file vma may be anonymous pages due to
> COW but they can't be THP so it won't trigger THP numa fault at all. I
> think this is why no bug was reported. I overlooked this in the first
> place.
>
> Your fix is correct, and please add the above justification to your commit log.

BTW, I think you can just undo or revert commit c77c5cbafe54 ("mm:
migrate: skip shared exec THP for NUMA balancing").

Thanks,
Yang

>
> Reviewed-by: Yang Shi <shy828301@gmail.com>
>
> >
> > Fixes: c77c5cbafe54 ("mm: migrate: skip shared exec THP for NUMA balancing")
> > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> > ---
> >  mm/migrate.c | 4 ----
> >  1 file changed, 4 deletions(-)
> >
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index 5357a8527ca2..68bfa1625898 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -2192,9 +2192,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
> >         int page_lru = page_is_file_lru(page);
> >         unsigned long start = address & HPAGE_PMD_MASK;
> >
> > -       if (is_shared_exec_page(vma, page))
> > -               goto out;
> > -
> >         new_page = alloc_pages_node(node,
> >                 (GFP_TRANSHUGE_LIGHT | __GFP_THISNODE),
> >                 HPAGE_PMD_ORDER);
> > @@ -2306,7 +2303,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
> >
> >  out_unlock:
> >         unlock_page(page);
> > -out:
> >         put_page(page);
> >         return 0;
> >  }
> > --
> > 2.19.1
> >


  reply	other threads:[~2021-03-24  1:16 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-23 13:54 [PATCH v2 0/5] Cleanup and fixup for mm/migrate.c Miaohe Lin
2021-03-23 13:54 ` [PATCH v2 1/5] mm/migrate.c: remove unnecessary VM_BUG_ON_PAGE on putback_movable_page() Miaohe Lin
2021-03-23 14:27   ` David Hildenbrand
2021-03-24  2:40     ` Miaohe Lin
2021-03-23 17:58   ` Yang Shi
2021-03-24  2:37     ` Miaohe Lin
2021-03-23 13:54 ` [PATCH v2 2/5] mm/migrate.c: remove unnecessary rc != MIGRATEPAGE_SUCCESS check in 'else' case Miaohe Lin
2021-03-23 17:46   ` Yang Shi
2021-03-23 13:54 ` [PATCH v2 3/5] mm/migrate.c: fix potential indeterminate pte entry in migrate_vma_insert_page() Miaohe Lin
2021-03-23 13:54 ` [PATCH v2 4/5] mm/migrate.c: use helper migrate_vma_collect_skip() in migrate_vma_collect_hole() Miaohe Lin
2021-03-23 13:54 ` [PATCH v2 5/5] mm/migrate.c: fix potential deadlock in NUMA balancing shared exec THP case Miaohe Lin
2021-03-23 17:17   ` Yang Shi
2021-03-24  1:16     ` Yang Shi [this message]
2021-03-24  2:14       ` Miaohe Lin
2021-03-24  2:03     ` Miaohe Lin

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