linux-kernel - Re: [PATCH] fix hugetlbfs hwpoison handling

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Date: Thu, 11 Jan 2024 11:21:12 -0800
From: Sidhartha Kumar <sidhartha.kumar@...cle.com>
To: linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc: akpm@...ux-foundation.org, usama.anjum@...labora.com,
        muchun.song@...ux.dev, jiaqiyan@...gle.com, willy@...radead.org,
        linmiaohe@...wei.com, naoya.horiguchi@....com, shy828301@...il.com,
        jthoughton@...gle.com, jane.chu@...cle.com, stable@...r.kernel.org
Subject: Re: [PATCH] fix hugetlbfs hwpoison handling

On 1/11/24 11:16 AM, Sidhartha Kumar wrote:
> has_extra_refcount() makes the assumption that a ref count of 1 means
> the page is not referenced by other users. 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 check if the page is not referenced by other users by checking
> the page count against 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@...r.kernel.org> # 6.7+
> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>
> Reported-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
> Tested-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
> ---
>   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..87f6bf7d8bc1 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -973,7 +973,7 @@ struct page_state {
>   static bool has_extra_refcount(struct page_state *ps, struct page *p,
>   			       bool extra_pins)
>   {
> -	int count = page_count(p) - 1;
> +	int count = page_count(p) - folio_nr_pages(page_folio(p));
>   
>   	if (extra_pins)
>   		count -= 1;

the patch title is missing a fs/hugetlbfs: prefix, could this be added Andrew?

Thanks,
Sidhartha