On 2021/4/9 7:25, Mike Kravetz wrote:
> 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.
Yes, a potential *theoretical* 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.
>
I will drop this. This does not worth backport.
>> Signed-off-by: Miaohe Lin <linmia...@huawei.com>
>> ---
>> 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".
>
Will add it in v2. Many thanks for review and nice suggestion ! :)
