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    Subject[PATCH v4 1/3] mm/hwpoison: mf_mutex for soft offline and unpoison
    Date
    From: Naoya Horiguchi <naoya.horiguchi@nec.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_mutex to soft offline and unpoison.
    The memory failure handler and soft offline handler get simpler with this.

    Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
    Reviewed-by: Yang Shi <shy828301@gmail.com>
    ---
    ChangeLog v4:
    - fix type in commit description.

    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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