Re: [PATCH] mm/page_alloc: release isolated freepages on compound range mismatch

["Zi Yan" <ziy@nvidia.com>]

On Mon Nov 2, 2026 at 5:10 AM EST, David Hildenbrand (Arm) wrote:
> On 11/2/26 10:29, Zhenghui Hao wrote:
>> 
>> On 2026/11/2 17:11, David Hildenbrand (Arm) wrote:
>>> On 11/2/26 10:06, Zhenghui Hao wrote:
>>>> alloc_contig_frozen_range_noprof() isolates [outer_start, outer_end)
>>>> before checking whether a __GFP_COMP request exactly matches the
>>>> allocated range.  If it does not, the function returns -EINVAL without
>>>> releasing cc.freepages, leaking the isolated pages.
>>>>
>>>> Call release_free_list() before returning -EINVAL, while the pageblock
>>>> is still isolated, matching the cleanup already used when
>>>> isolate_freepages_range() fails.
>>>>
>>>> Use WARN_ONCE() as well: the condition is reachable through the exported
>>>> API, and repeated invalid calls should not flood dmesg.
>>>>
>>>> Tested with an order-9 free pageblock and a one-page __GFP_COMP
>>>> subrange:
>>>>   before: free_buddy=0, leaked=512/512
>>>>   after:  free_buddy=1, leaked=0/512
>>> How did you reproduce this? Using a hacky kernel module?
>>>
>>>> Fixes: e98337d11bbdf ("mm/contig_alloc: support __GFP_COMP")
>>> I thought we discussed this in the past: if you are able to trigger the WARN
>>> something is messed up already.
>>>
>>>
>>> And indeed, same patch already here, SMH
>>>
>>> https://lore.kernel.org/linux-mm/20260629-free-pfn-on-alloc-contig-range-error-path-v1-1-496ff9ca22db@nvidia.com/
>> Thanks for the pointer, and sorry for the duplicate -- I missed the
>> earlier thread.
>> 
>> You're right on both points: the reproducer was a synthetic module, not a
>> real workload, and being able to trigger the WARN means the underlying
>> path or validation needs fixing rather than papering over it with
>> WARN_ONCE.
>> 
>> I'll drop this version and follow the existing thread. I'll check whether
>> the earlier patch is still pending and only send an update if there is a
>> real delta on the current tree.
>
> @Zi, are you still intending to follow up on the things we discussed in that thread?

Yes, I have the patch locally and will send it out today.


-- 
Best Regards,
Yan, Zi