linux-kernel - Re: [PATCH v2 2/4] mm/hwpoison: remove race consideration

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Message-ID: <CAHbLzkrUb4YcnuXY9MYs+afRCFSfNdTmJAYyqHPxnqrEdFehhA@mail.gmail.com>
Date:   Tue, 26 Oct 2021 18:04:13 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>
Cc:     Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        Ding Hui <dinghui@...gfor.com.cn>,
        Tony Luck <tony.luck@...el.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Peter Xu <peterx@...hat.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] mm/hwpoison: remove race consideration

On Mon, Oct 25, 2021 at 4:06 PM Naoya Horiguchi
<naoya.horiguchi@...ux.dev> wrote:
>
> From: Naoya Horiguchi <naoya.horiguchi@....com>
>
> Now memory_failure() and unpoison_memory() are protected by mf_mutex,
> so no need to explicitly check races between them.  So remove them.

It seems this patch could be folded into patch #1. Some "unlock_mutex"
were added by patch #1 then they were removed by this patch
immediately, it seems a bit of a waste and this patch is actually the
by-product of patch #1.

>
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
> ---
>  mm/memory-failure.c | 37 -------------------------------------
>  1 file changed, 37 deletions(-)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 97297edfbd8e..a47b741ca04b 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1507,14 +1507,6 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
>         lock_page(head);
>         page_flags = head->flags;
>
> -       if (!PageHWPoison(head)) {
> -               pr_err("Memory failure: %#lx: just unpoisoned\n", pfn);
> -               num_poisoned_pages_dec();
> -               unlock_page(head);
> -               put_page(head);
> -               return 0;
> -       }
> -
>         /*
>          * TODO: hwpoison for pud-sized hugetlb doesn't work right now, so
>          * simply disable it. In order to make it work properly, we need
> @@ -1789,16 +1781,6 @@ int memory_failure(unsigned long pfn, int flags)
>          */
>         page_flags = p->flags;
>
> -       /*
> -        * unpoison always clear PG_hwpoison inside page lock
> -        */
> -       if (!PageHWPoison(p)) {
> -               pr_err("Memory failure: %#lx: just unpoisoned\n", pfn);
> -               num_poisoned_pages_dec();
> -               unlock_page(p);
> -               put_page(p);
> -               goto unlock_mutex;
> -       }
>         if (hwpoison_filter(p)) {
>                 if (TestClearPageHWPoison(p))
>                         num_poisoned_pages_dec();
> @@ -2016,17 +1998,6 @@ int unpoison_memory(unsigned long pfn)
>                 goto unlock_mutex;
>         }
>
> -       /*
> -        * unpoison_memory() can encounter thp only when the thp is being
> -        * worked by memory_failure() and the page lock is not held yet.
> -        * In such case, we yield to memory_failure() and make unpoison fail.
> -        */
> -       if (!PageHuge(page) && PageTransHuge(page)) {
> -               unpoison_pr_info("Unpoison: Memory failure is now running on %#lx\n",
> -                                pfn, &unpoison_rs);
> -               goto unlock_mutex;
> -       }
> -
>         if (!get_hwpoison_page(p, flags)) {
>                 if (TestClearPageHWPoison(p))
>                         num_poisoned_pages_dec();
> @@ -2035,20 +2006,12 @@ int unpoison_memory(unsigned long pfn)
>                 goto unlock_mutex;
>         }
>
> -       lock_page(page);
> -       /*
> -        * This test is racy because PG_hwpoison is set outside of page lock.
> -        * That's acceptable because that won't trigger kernel panic. Instead,
> -        * the PG_hwpoison page will be caught and isolated on the entrance to
> -        * the free buddy page pool.
> -        */
>         if (TestClearPageHWPoison(page)) {
>                 unpoison_pr_info("Unpoison: Software-unpoisoned page %#lx\n",
>                                  pfn, &unpoison_rs);
>                 num_poisoned_pages_dec();
>                 freeit = 1;
>         }
> -       unlock_page(page);
>
>         put_page(page);
>         if (freeit && !(pfn == my_zero_pfn(0) && page_count(p) == 1))
> --
> 2.25.1
>