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Date: Fri, 5 Nov 2021 11:23:47 -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 v3 1/3] mm/hwpoison: mf_mutex for soft offline and unpoison
On Thu, Nov 4, 2021 at 10:52 PM Naoya Horiguchi
<naoya.horiguchi@...ux.dev> wrote:
>
> From: Naoya Horiguchi <naoya.horiguchi@....com>
>
> Originally mf_mutex is introduced to serialize multiple MCE events, but
> it is not that useful to allow unpoison to run in parallel with memory_failure()
> and soft offline. So apply mf_they to soft offline and unpoison.
^^^^^^^^
A typo? It should be mf_mutex, right?
Looks good to me other than the above nit. Reviewed-by: Yang Shi
<shy828301@...il.com>
> The memory failure handler and soft offline handler get simpler with this.
>
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
> ---
> ChangeLog v3:
> - merge with "mm/hwpoison: remove race consideration"
> - update description
>
> ChangeLog v2:
> - add mutex_unlock() in "page already poisoned" path in soft_offline_page().
> (Thanks to Ding Hui)
> ---
> mm/memory-failure.c | 62 +++++++++++++--------------------------------
> 1 file changed, 18 insertions(+), 44 deletions(-)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index e8c38e27b753..d29c79de6034 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
> @@ -1628,6 +1620,8 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
> return rc;
> }
>
> +static DEFINE_MUTEX(mf_mutex);
> +
> /**
> * memory_failure - Handle memory failure of a page.
> * @pfn: Page Number of the corrupted page
> @@ -1654,7 +1648,6 @@ int memory_failure(unsigned long pfn, int flags)
> int res = 0;
> unsigned long page_flags;
> bool retry = true;
> - static DEFINE_MUTEX(mf_mutex);
>
> if (!sysctl_memory_failure_recovery)
> panic("Memory failure on page %lx", pfn);
> @@ -1788,16 +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();
> @@ -1978,6 +1961,7 @@ int unpoison_memory(unsigned long pfn)
> struct page *page;
> struct page *p;
> int freeit = 0;
> + int ret = 0;
> unsigned long flags = 0;
> static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
> DEFAULT_RATELIMIT_BURST);
> @@ -1988,39 +1972,30 @@ int unpoison_memory(unsigned long pfn)
> p = pfn_to_page(pfn);
> page = compound_head(p);
>
> + mutex_lock(&mf_mutex);
> +
> if (!PageHWPoison(p)) {
> unpoison_pr_info("Unpoison: Page was already unpoisoned %#lx\n",
> pfn, &unpoison_rs);
> - return 0;
> + goto unlock_mutex;
> }
>
> if (page_count(page) > 1) {
> unpoison_pr_info("Unpoison: Someone grabs the hwpoison page %#lx\n",
> pfn, &unpoison_rs);
> - return 0;
> + goto unlock_mutex;
> }
>
> if (page_mapped(page)) {
> unpoison_pr_info("Unpoison: Someone maps the hwpoison page %#lx\n",
> pfn, &unpoison_rs);
> - return 0;
> + goto unlock_mutex;
> }
>
> if (page_mapping(page)) {
> unpoison_pr_info("Unpoison: the hwpoison page has non-NULL mapping %#lx\n",
> pfn, &unpoison_rs);
> - return 0;
> - }
> -
> - /*
> - * 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);
> - return 0;
> + goto unlock_mutex;
> }
>
> if (!get_hwpoison_page(p, flags)) {
> @@ -2028,29 +2003,23 @@ int unpoison_memory(unsigned long pfn)
> num_poisoned_pages_dec();
> unpoison_pr_info("Unpoison: Software-unpoisoned free page %#lx\n",
> pfn, &unpoison_rs);
> - return 0;
> + 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))
> put_page(page);
>
> - return 0;
> +unlock_mutex:
> + mutex_unlock(&mf_mutex);
> + return ret;
> }
> EXPORT_SYMBOL(unpoison_memory);
>
> @@ -2231,9 +2200,12 @@ int soft_offline_page(unsigned long pfn, int flags)
> return -EIO;
> }
>
> + mutex_lock(&mf_mutex);
> +
> if (PageHWPoison(page)) {
> pr_info("%s: %#lx page already poisoned\n", __func__, pfn);
> put_ref_page(ref_page);
> + mutex_unlock(&mf_mutex);
> return 0;
> }
>
> @@ -2251,5 +2223,7 @@ int soft_offline_page(unsigned long pfn, int flags)
> }
> }
>
> + mutex_unlock(&mf_mutex);
> +
> return ret;
> }
> --
> 2.25.1
>
>
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