On 05/17/23 16:09, Jiaqi Yan wrote:
> When a hugepage contains HWPOISON pages, read() fails to read any byte
> of the hugepage and returns -EIO, although many bytes in the HWPOISON
> hugepage are readable.
>
> Improve this by allowing hugetlbfs_read_iter returns as many bytes as
> possible. For a requested range [offset, offset + len) that contains
> HWPOISON page, return [offset, first HWPOISON page addr); the next read
> attempt will fail and return -EIO.
>
> Signed-off-by: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
> ---
> fs/hugetlbfs/inode.c | 62 +++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 56 insertions(+), 6 deletions(-)
>
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index ecfdfb2529a3..1baa08ec679f 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -282,6 +282,46 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
> }
> #endif
>
> +/*
> + * Someone wants to read @bytes from a HWPOISON hugetlb @page from @offset.
> + * Returns the maximum number of bytes one can read without touching the 1st raw
> + * HWPOISON subpage.
> + *
> + * The implementation borrows the iteration logic from copy_page_to_iter*.
> + */
> +static size_t adjust_range_hwpoison(struct page *page, size_t offset, size_t bytes)
> +{
> + size_t n = 0;
> + size_t res = 0;
> + struct folio *folio = page_folio(page);
> +
> + folio_lock(folio);
What is the reason for taking folio_lock?
> +
> + /* First subpage to start the loop. */
> + page += offset / PAGE_SIZE;
> + offset %= PAGE_SIZE;
> + while (1) {
> + if (find_raw_hwp_page(folio, page) != NULL)
> + break;
> +
> + /* Safe to read n bytes without touching HWPOISON subpage. */
> + n = min(bytes, (size_t)PAGE_SIZE - offset);
> + res += n;
> + bytes -= n;
> + if (!bytes || !n)
> + break;
> + offset += n;
> + if (offset == PAGE_SIZE) {
> + page++;
> + offset = 0;
> + }
> + }
> +
> + folio_unlock(folio);
> +
> + return res;
> +}
> +
> /*
> * Support for read() - Find the page attached to f_mapping and copy out the
> * data. This provides functionality similar to filemap_read().
> @@ -300,7 +340,7 @@ static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
>
> while (iov_iter_count(to)) {
> struct page *page;
> - size_t nr, copied;
> + size_t nr, copied, want;
>
> /* nr is the maximum number of bytes to copy from this page */
> nr = huge_page_size(h);
> @@ -328,16 +368,26 @@ static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
> } else {
> unlock_page(page);
>
> - if (PageHWPoison(page)) {
> - put_page(page);
> - retval = -EIO;
> - break;
> + if (!PageHWPoison(page))
> + want = nr;
> + else {
> + /*
> + * Adjust how many bytes safe to read without
> + * touching the 1st raw HWPOISON subpage after
> + * offset.
> + */
> + want = adjust_range_hwpoison(page, offset, nr);
> + if (want == 0) {
> + put_page(page);
> + retval = -EIO;
> + break;
> + }
> }
>
> /*
> * We have the page, copy it to user space buffer.
> */
> - copied = copy_page_to_iter(page, offset, nr, to);
> + copied = copy_page_to_iter(page, offset, want, to);
> put_page(page);
> }
> offset += copied;
> --
> 2.40.1.606.ga4b1b128d6-goog
>
Code looks fine, just wondering about that folio_lock.
--
Mike Kravetz
