On 11/14/24 07:57, Qiang Liu wrote:
> It is impossible for the situation where blockpfn > end_pfn to arise,
> The if statement here is not only unnecessary, but may also lead to
> a misunderstanding that blockpfn > end_pfn could potentially happen.
> so these unnecessary checking code should be removed.
>
> Signed-off-by: Qiang Liu <liuq131@xxxxxxxxxxxxxxx>
I see that's since 3da0272a4c7d ("mm/compaction: correctly return failure
with bogus compound_order in strict mode")
I think that commit introduced a risk of overflow due to a bogus order
(which we read in a racy way), and once blockpfn overflows it will satisfy
<= end_pfn and might e.g. end up scanning a completely different zone?
if (blockpfn + (1UL << order) <= end_pfn) {
blockpfn += (1UL << order) - 1;
page += (1UL << order) - 1;
nr_scanned += (1UL << order) - 1;
}
We should better add back the MAX_ORDER sanity check?
> ---
> mm/compaction.c | 6 ------
> 1 file changed, 6 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index a2b16b08cbbf..baeda7132252 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -682,12 +682,6 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
> if (locked)
> spin_unlock_irqrestore(&cc->zone->lock, flags);
>
> - /*
> - * Be careful to not go outside of the pageblock.
> - */
> - if (unlikely(blockpfn > end_pfn))
> - blockpfn = end_pfn;
> -
> trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
> nr_scanned, total_isolated);
>
