On Fri, Sep 01, 2023 at 11:51:38PM +0800, Kemeng Shi wrote:
> In strict mode, we should return 0 if there is any hole in pageblock. If
> we successfully isolated pages at beginning at pageblock and then have a
> bogus compound_order outside pageblock in next page. We will abort search
> loop with blockpfn > end_pfn. Although we will limit blockpfn to end_pfn,
> we will treat it as a successful isolation in strict mode as blockpfn is
> not < end_pfn and return partial isolated pages. Then
> isolate_freepages_range may success unexpectly with hole in isolated
> range.
>
> Fixes: 9fcd6d2e052e ("mm, compaction: skip compound pages by order in free scanner")
> Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> ---
> mm/compaction.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index a40550a33aee..9ecbfbc695e5 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -626,11 +626,12 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
> if (PageCompound(page)) {
> const unsigned int order = compound_order(page);
>
> - if (likely(order <= MAX_ORDER)) {
> + if (blockpfn + (1UL << order) <= end_pfn) {
> blockpfn += (1UL << order) - 1;
> page += (1UL << order) - 1;
> nr_scanned += (1UL << order) - 1;
> }
> +
> goto isolate_fail;
> }
>
> @@ -678,8 +679,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
> spin_unlock_irqrestore(&cc->zone->lock, flags);
>
> /*
> - * There is a tiny chance that we have read bogus compound_order(),
> - * so be careful to not go outside of the pageblock.
> + * Be careful to not go outside of the pageblock.
> */
> if (unlikely(blockpfn > end_pfn))
> blockpfn = end_pfn;
Is this check still necessary after the first hunk?
--
Mel Gorman
SUSE Labs
