Re: [PATCH] hugetlb: fix uninitialized subpool pointer

[Mike Kravetz]

On 2/23/21 2:45 PM, Oscar Salvador wrote:
> On Tue, Feb 23, 2021 at 01:55:44PM -0800, Mike Kravetz wrote:
>> Gerald Schaefer reported a panic on s390 in hugepage_subpool_put_pages()
>> with linux-next 5.12.0-20210222.
>> Call trace:
>>   hugepage_subpool_put_pages.part.0+0x2c/0x138
>>   __free_huge_page+0xce/0x310
>>   alloc_pool_huge_page+0x102/0x120
>>   set_max_huge_pages+0x13e/0x350
>>   hugetlb_sysctl_handler_common+0xd8/0x110
>>   hugetlb_sysctl_handler+0x48/0x58
>>   proc_sys_call_handler+0x138/0x238
>>   new_sync_write+0x10e/0x198
>>   vfs_write.part.0+0x12c/0x238
>>   ksys_write+0x68/0xf8
>>   do_syscall+0x82/0xd0
>>   __do_syscall+0xb4/0xc8
>>   system_call+0x72/0x98
>>
>> This is a result of the change which moved the hugetlb page subpool
>> pointer from page->private to page[1]->private.  When new pages are
>> allocated from the buddy allocator, the private field of the head
>> page will be cleared, but the private field of subpages is not modified.
>> Therefore, old values may remain.
>>
>> Fix by initializing hugetlb page subpool pointer in prep_new_huge_page().
>>
>> Fixes: f1280272ae4d ("hugetlb: use page.private for hugetlb specific page flags")
>> Reported-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
>> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> 
> Do we need the hugetlb_set_page_subpool() in __free_huge_page?

Yes, that is the more common case where the once active hugetlb page
will be simply added to the free list via enqueue_huge_page().  This
path does not go through prep_new_huge_page.

-- 
Mike Kravetz