linux-kernel - Re: [PATCH v1] mm/huge_memory.c: warn with pr_warn_ratelimited instead of VM_WARN_ON_ONCE

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Date:   Thu, 6 Apr 2023 15:57:43 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Xu Yu <xuyu@...ux.alibaba.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Naoya Horiguchi <naoya.horiguchi@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] mm/huge_memory.c: warn with pr_warn_ratelimited
 instead of VM_WARN_ON_ONCE_FOLIO

On Thu, Apr 6, 2023 at 1:20 AM Naoya Horiguchi
<naoya.horiguchi@...ux.dev> wrote:
>
> From: Naoya Horiguchi <naoya.horiguchi@....com>
>
> split_huge_page_to_list() WARNs when called for huge zero pages, which
> sounds to me too harsh because it does not imply a kernel bug, but just
> notifies the event to admins.  On the other hand, this is considered
> as critical by syzkaller and makes its testing less efficient, which
> seems to me harmful.
>
> So replace the VM_WARN_ON_ONCE_FOLIO with pr_warn_ratelimited.

Makes sense to me. Reviewed-by: Yang Shi <shy828301@...il.com>

>
> Fixes: 478d134e9506 ("mm/huge_memory: do not overkill when splitting huge_zero_page")
> Reported-by: syzbot+07a218429c8d19b1fb25@...kaller.appspotmail.com
> Link: https://lore.kernel.org/lkml/000000000000a6f34a05e6efcd01@google.com/
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
> Cc: stable@...r.kernel.org
> ---
>  mm/huge_memory.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 81a5689806af..06bcdd6f5060 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2649,9 +2649,10 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>         VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
>
>         is_hzp = is_huge_zero_page(&folio->page);
> -       VM_WARN_ON_ONCE_FOLIO(is_hzp, folio);
> -       if (is_hzp)
> +       if (is_hzp) {
> +               pr_warn_ratelimited("Called split_huge_page for huge zero page\n");
>                 return -EBUSY;
> +       }
>
>         if (folio_test_writeback(folio))
>                 return -EBUSY;
> --
> 2.25.1
>