On 4/2/21 2:32 AM, Miaohe Lin wrote:
> A rare out of memory error would prevent removal of the reserve map region
> for a page. hugetlb_fix_reserve_counts() handles this rare case to avoid
> dangling with incorrect counts. Unfortunately, hugepage_subpool_get_pages
> and hugetlb_acct_memory could possibly fail too. We should correctly handle
> these cases.
Yes, this is a potential issue.
The 'good news' is that hugetlb_fix_reserve_counts() is unlikely to ever
be called. To do so would imply we could not allocate a region entry
which is only 6 words in size. We also keep a 'cache' of entries so we
may not even need to allocate.
But, as mentioned it is a potential issue.
> Fixes: b5cec28d36f5 ("hugetlbfs: truncate_hugepages() takes a range of pages")
This is likely going to make this get picked by by stable releases.
That is unfortunate as mentioned above this is mostly theoretical.
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> ---
> mm/hugetlb.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index bdff8d23803f..ca5464ed04b7 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -745,13 +745,20 @@ void hugetlb_fix_reserve_counts(struct inode *inode)
> {
> struct hugepage_subpool *spool = subpool_inode(inode);
> long rsv_adjust;
> + bool reserved = false;
>
> rsv_adjust = hugepage_subpool_get_pages(spool, 1);
> - if (rsv_adjust) {
> + if (rsv_adjust > 0) {
> struct hstate *h = hstate_inode(inode);
>
> - hugetlb_acct_memory(h, 1);
> + if (!hugetlb_acct_memory(h, 1))
> + reserved = true;
> + } else if (!rsv_adjust) {
> + reserved = true;
> }
> +
> + if (!reserved)
> + pr_warn("hugetlb: fix reserve count failed\n");
We should expand this warning message a bit to indicate what this may
mean to the user. Add something like"
"Huge Page Reserved count may go negative".
--
Mike Kravetz
