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    SubjectRe: [PATCH v5 2/2] mm: fix the handling Non-LRU pages returned by follow_page
    From
    Am 2022-08-15 um 03:02 schrieb Haiyue Wang:
    > The handling Non-LRU pages returned by follow_page() jumps directly, it
    > doesn't call put_page() to handle the reference count, since 'FOLL_GET'
    > flag for follow_page() has get_page() called. Fix the zone device page
    > check by handling the page reference count correctly before returning.
    >
    > And as David reviewed, "device pages are never PageKsm pages". Drop this
    > zone device page check for break_ksm().
    >
    > Fixes: 3218f8712d6b ("mm: handling Non-LRU pages returned by vm_normal_pages")
    > Signed-off-by: Haiyue Wang <haiyue.wang@intel.com>

    Thank you for catching this. The patch is

    Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>


    > ---
    > mm/huge_memory.c | 4 ++--
    > mm/ksm.c | 12 +++++++++---
    > mm/migrate.c | 10 +++++++---
    > 3 files changed, 18 insertions(+), 8 deletions(-)
    >
    > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
    > index 8a7c1b344abe..b2ba17c3dcd7 100644
    > --- a/mm/huge_memory.c
    > +++ b/mm/huge_memory.c
    > @@ -2963,10 +2963,10 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
    > /* FOLL_DUMP to ignore special (like zero) pages */
    > page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
    >
    > - if (IS_ERR_OR_NULL(page) || is_zone_device_page(page))
    > + if (IS_ERR_OR_NULL(page))
    > continue;
    >
    > - if (!is_transparent_hugepage(page))
    > + if (is_zone_device_page(page) || !is_transparent_hugepage(page))
    > goto next;
    >
    > total++;
    > diff --git a/mm/ksm.c b/mm/ksm.c
    > index 42ab153335a2..e26f57fc1f0e 100644
    > --- a/mm/ksm.c
    > +++ b/mm/ksm.c
    > @@ -475,7 +475,7 @@ static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
    > cond_resched();
    > page = follow_page(vma, addr,
    > FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
    > - if (IS_ERR_OR_NULL(page) || is_zone_device_page(page))
    > + if (IS_ERR_OR_NULL(page))
    > break;
    > if (PageKsm(page))
    > ret = handle_mm_fault(vma, addr,
    > @@ -560,12 +560,15 @@ static struct page *get_mergeable_page(struct rmap_item *rmap_item)
    > goto out;
    >
    > page = follow_page(vma, addr, FOLL_GET);
    > - if (IS_ERR_OR_NULL(page) || is_zone_device_page(page))
    > + if (IS_ERR_OR_NULL(page))
    > goto out;
    > + if (is_zone_device_page(page))
    > + goto out_putpage;
    > if (PageAnon(page)) {
    > flush_anon_page(vma, page, addr);
    > flush_dcache_page(page);
    > } else {
    > +out_putpage:
    > put_page(page);
    > out:
    > page = NULL;
    > @@ -2308,11 +2311,13 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page)
    > if (ksm_test_exit(mm))
    > break;
    > *page = follow_page(vma, ksm_scan.address, FOLL_GET);
    > - if (IS_ERR_OR_NULL(*page) || is_zone_device_page(*page)) {
    > + if (IS_ERR_OR_NULL(*page)) {
    > ksm_scan.address += PAGE_SIZE;
    > cond_resched();
    > continue;
    > }
    > + if (is_zone_device_page(*page))
    > + goto next_page;
    > if (PageAnon(*page)) {
    > flush_anon_page(vma, *page, ksm_scan.address);
    > flush_dcache_page(*page);
    > @@ -2327,6 +2332,7 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page)
    > mmap_read_unlock(mm);
    > return rmap_item;
    > }
    > +next_page:
    > put_page(*page);
    > ksm_scan.address += PAGE_SIZE;
    > cond_resched();
    > diff --git a/mm/migrate.c b/mm/migrate.c
    > index 581dfaad9257..fee12cd2f294 100644
    > --- a/mm/migrate.c
    > +++ b/mm/migrate.c
    > @@ -1672,9 +1672,12 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
    > goto out;
    >
    > err = -ENOENT;
    > - if (!page || is_zone_device_page(page))
    > + if (!page)
    > goto out;
    >
    > + if (is_zone_device_page(page))
    > + goto out_putpage;
    > +
    > err = 0;
    > if (page_to_nid(page) == node)
    > goto out_putpage;
    > @@ -1868,8 +1871,9 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
    > if (IS_ERR(page))
    > goto set_status;
    >
    > - if (page && !is_zone_device_page(page)) {
    > - err = page_to_nid(page);
    > + if (page) {
    > + err = !is_zone_device_page(page) ? page_to_nid(page)
    > + : -ENOENT;
    > if (foll_flags & FOLL_GET)
    > put_page(page);
    > } else {

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