Re: [PATCH 1/1] mm: protect xa split stuff under lruvec->lru_lock during migration

[Zhaoyang Huang]

On Tue, May 21, 2024 at 11:47 PM Marcin Wanat <private@xxxxxxxxxxxxxx> wrote:
>
> On 21.05.2024 03:00, Zhaoyang Huang wrote:
> > On Tue, May 21, 2024 at 8:58 AM Zhaoyang Huang <huangzhaoyang@xxxxxxxxx> wrote:
> >>
> >> On Tue, May 21, 2024 at 3:42 AM Marcin Wanat <private@xxxxxxxxxxxxxx> wrote:
> >>>
> >>> On 15.04.2024 03:50, Zhaoyang Huang wrote:
> >>> I have around 50 hosts handling high I/O (each with 20Gbps+ uplinks
> >>> and multiple NVMe drives), running RockyLinux 8/9. The stock RHEL
> >>> kernel 8/9 is NOT affected, and the long-term kernel 5.15.X is NOT affected.
> >>> However, with long-term kernels 6.1.XX and 6.6.XX,
> >>> (tested at least 10 different versions), this lockup always appears
> >>> after 2-30 days, similar to the report in the original thread.
> >>> The more load (for example, copying a lot of local files while
> >>> serving 20Gbps traffic), the higher the chance that the bug will appear.
> >>>
> >>> I haven't been able to reproduce this during synthetic tests,
> >>> but it always occurs in production on 6.1.X and 6.6.X within 2-30 days.
> >>> If anyone can provide a patch, I can test it on multiple machines
> >>> over the next few days.
> >> Could you please try this one which could be applied on 6.6 directly. Thank you!
> > URL: https://lore.kernel.org/linux-mm/20240412064353.133497-1-zhaoyang.huang@xxxxxxxxxx/
> >
>
> Unfortunately, I am unable to cleanly apply this patch against the
> latest 6.6.31
Please try below one which works on my v6.6 based android. Thank you
for your test in advance :D

mm/huge_memory.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 064fbd90822b..5899906c326a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2498,7 +2498,7 @@ static void __split_huge_page(struct page *page,
struct list_head *list,
 {
  struct folio *folio = page_folio(page);
  struct page *head = &folio->page;
- struct lruvec *lruvec;
+ struct lruvec *lruvec = folio_lruvec(folio);
  struct address_space *swap_cache = NULL;
  unsigned long offset = 0;
  unsigned int nr = thp_nr_pages(head);
@@ -2513,9 +2513,6 @@ static void __split_huge_page(struct page *page,
struct list_head *list,
  xa_lock(&swap_cache->i_pages);
  }

- /* lock lru list/PageCompound, ref frozen by page_ref_freeze */
- lruvec = folio_lruvec_lock(folio);
-
  ClearPageHasHWPoisoned(head);

  for (i = nr - 1; i >= 1; i--) {
@@ -2541,9 +2538,6 @@ static void __split_huge_page(struct page *page,
struct list_head *list,
  }

  ClearPageCompound(head);
- unlock_page_lruvec(lruvec);
- /* Caller disabled irqs, so they are still disabled here */
-
  split_page_owner(head, nr);

  /* See comment in __split_huge_page_tail() */
@@ -2560,7 +2554,6 @@ static void __split_huge_page(struct page *page,
struct list_head *list,
  page_ref_add(head, 2);
  xa_unlock(&head->mapping->i_pages);
  }
- local_irq_enable();

  if (nr_dropped)
  shmem_uncharge(head->mapping->host, nr_dropped);
@@ -2631,6 +2624,7 @@ int split_huge_page_to_list(struct page *page,
struct list_head *list)
  int extra_pins, ret;
  pgoff_t end;
  bool is_hzp;
+ struct lruvec *lruvec;

  VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
  VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
@@ -2714,6 +2708,14 @@ int split_huge_page_to_list(struct page *page,
struct list_head *list)

  /* block interrupt reentry in xa_lock and spinlock */
  local_irq_disable();
+
+ /*
+ * take lruvec's lock before freeze the folio to prevent the folio
+ * remains in the page cache with refcnt == 0, which could lead to
+ * find_get_entry enters livelock by iterating the xarray.
+ */
+ lruvec = folio_lruvec_lock(folio);
+
  if (mapping) {
  /*
  * Check if the folio is present in page cache.
@@ -2748,12 +2750,16 @@ int split_huge_page_to_list(struct page *page,
struct list_head *list)
  }

  __split_huge_page(page, list, end);
+ unlock_page_lruvec(lruvec);
+ local_irq_enable();
  ret = 0;
  } else {
  spin_unlock(&ds_queue->split_queue_lock);
 fail:
  if (mapping)
  xas_unlock(&xas);
+
+ unlock_page_lruvec(lruvec);
  local_irq_enable();
  remap_page(folio, folio_nr_pages(folio));
  ret = -EAGAIN;
-- 
2.25.1