Re: [PATCH RFC 0/2] mm/page_alloc: free_pcppages_bulk safeguard

[Kemeng Shi <shikemeng@huaweicloud.com>]

on 8/21/2023 6:32 PM, Mel Gorman wrote:
> On Thu, Aug 17, 2023 at 11:05:22PM -0700, Chris Li wrote:
>> In this patch series I want to safeguard
>> the free_pcppage_bulk against change in the
>> pcp->count outside of this function. e.g.
>> by BPF program inject on the function tracepoint.
>>
>> I break up the patches into two seperate patches
>> for the safeguard and clean up.
>>
>> Hopefully that is easier to review.
>>
>> Signed-off-by: Chris Li <chrisl@kernel.org>
> 
> This sounds like a maintenance nightmare if internal state can be arbitrary
> modified by a BPF program and still expected to work properly in all cases.
> Every review would have to take into account "what if a BPF script modifies
> state behind our back?"
> 
Agreed. We assume pcp->count is protected by pcp->lock. Instead of make code
work in case pcp->count could be changed without lock held, it's more reasonble
to modify pcp->count with pcp->lock held in BPF program.