Re: [PATCH v2] fs/hugetlbfs/inode.c: mm/memory-failure.c: fix hugetlbfs hwpoison handling

[Muchun Song <muchun.song@linux.dev>]

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.com/T/#m8e1469119e5b831bbd05d495f96b842e4a1c5519
> 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",