On 2024/1/13 02:08, Sidhartha Kumar wrote:

has_extra_refcount() makes the assumption that the page cache adds a ref count of 1 and subtracts this in the extra_pins case. Commit a08c7193e4f1 (mm/filemap: remove hugetlb special casing in filemap.c) modifies __filemap_add_folio() by calling folio_ref_add(folio, nr); for all cases (including hugtetlb) where nr is the number of pages in the folio. We should adjust the number of references coming from the page cache by subtracing the number of pages rather than 1.

In hugetlbfs_read_iter(), folio_test_has_hwpoisoned() is testing the wrong flag as, in the hugetlb case, memory-failure code calls folio_test_set_hwpoison() to indicate poison. folio_test_hwpoison() is the correct function to test for that flag.

After these fixes, the hugetlb hwpoison read selftest passes all cases.

Fixes: a08c7193e4f1 ("mm/filemap: remove hugetlb special casing in filemap.c") Closes: https://lore.kernel.org/linux-mm/20230713001833.3778937-1-jiaqiyan@google.co... Cc: stable@vger.kernel.org # 6.7+ Signed-off-by: Sidhartha Kumar sidhartha.kumar@oracle.com Reported-by: Muhammad Usama Anjum usama.anjum@collabora.com

---

v1 -> v2: move ref_count adjustment to if(extra_pins) block as that represents ref counts from the page cache per Miaohe Lin.

fs/hugetlbfs/inode.c | 2 +- mm/memory-failure.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 36132c9125f9..3a248e4f7e93 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -340,7 +340,7 @@ static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to) } else { folio_unlock(folio);

• 	if (!folio_test_has_hwpoisoned(folio))
  

• 	if (!folio_test_hwpoison(folio))
  	want = nr;
  else {
  	/*
  

diff --git a/mm/memory-failure.c b/mm/memory-failure.c index d8c853b35dbb..ef7ae73b65bd 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -976,7 +976,7 @@ static bool has_extra_refcount(struct page_state *ps, struct page *p, int count = page_count(p) - 1; if (extra_pins)

• count -= 1;
  

• count -= folio_nr_pages(page_folio(p));
  

IIUC, It seems than this also fix shmem of THP, because has_extra_refcount() is called from me_pagecache_clean(), right?

if (count > 0) { pr_err("%#lx: %s still referenced by %d users\n",

On 2024/1/13 2:08, Sidhartha Kumar wrote:

has_extra_refcount() makes the assumption that the page cache adds a ref count of 1 and subtracts this in the extra_pins case. Commit a08c7193e4f1 (mm/filemap: remove hugetlb special casing in filemap.c) modifies __filemap_add_folio() by calling folio_ref_add(folio, nr); for all cases (including hugtetlb) where nr is the number of pages in the folio. We should adjust the number of references coming from the page cache by subtracing the number of pages rather than 1.

In hugetlbfs_read_iter(), folio_test_has_hwpoisoned() is testing the wrong flag as, in the hugetlb case, memory-failure code calls folio_test_set_hwpoison() to indicate poison. folio_test_hwpoison() is the correct function to test for that flag.

After these fixes, the hugetlb hwpoison read selftest passes all cases.

Fixes: a08c7193e4f1 ("mm/filemap: remove hugetlb special casing in filemap.c") Closes: https://lore.kernel.org/linux-mm/20230713001833.3778937-1-jiaqiyan@google.co... Cc: stable@vger.kernel.org # 6.7+ Signed-off-by: Sidhartha Kumar sidhartha.kumar@oracle.com Reported-by: Muhammad Usama Anjum usama.anjum@collabora.com

---

v1 -> v2: move ref_count adjustment to if(extra_pins) block as that represents ref counts from the page cache per Miaohe Lin.

Thanks for your update of patch.

fs/hugetlbfs/inode.c | 2 +- mm/memory-failure.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 36132c9125f9..3a248e4f7e93 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -340,7 +340,7 @@ static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to) } else { folio_unlock(folio);

• 	if (!folio_test_has_hwpoisoned(folio))
  

• 	if (!folio_test_hwpoison(folio))
  	want = nr;
  else {
  	/*
  

diff --git a/mm/memory-failure.c b/mm/memory-failure.c index d8c853b35dbb..ef7ae73b65bd 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -976,7 +976,7 @@ static bool has_extra_refcount(struct page_state *ps, struct page *p, int count = page_count(p) - 1; if (extra_pins)

• count -= 1;
  

• count -= folio_nr_pages(page_folio(p));
  

I think this should be the right solution. @extra_pins indicates the extra page refcnt from page cache.

Acked-by: Miaohe Lin linmiaohe@huawei.com Thanks.

if (count > 0) { pr_err("%#lx: %s still referenced by %d users\n",