On Thu 17-11-16 14:11:30, Johannes Weiner wrote:
> When a radix tree iteration drops the tree lock, another thread might
> swoop in and free the node holding the current slot. The iteration
> needs to do another tree lookup from the current index to continue.
>
> [kirill.shutemov@xxxxxxxxxxxxxxx: re-lookup for replacement]
> Fixes: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages")
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
The patch looks good. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> mm/khugepaged.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 728d7790dc2d..bdfdab40a813 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1401,6 +1401,9 @@ static void collapse_shmem(struct mm_struct *mm,
>
> spin_lock_irq(&mapping->tree_lock);
>
> + slot = radix_tree_lookup_slot(&mapping->page_tree, index);
> + VM_BUG_ON_PAGE(page != radix_tree_deref_slot_protected(slot,
> + &mapping->tree_lock), page);
> VM_BUG_ON_PAGE(page_mapped(page), page);
>
> /*
> @@ -1424,6 +1427,7 @@ static void collapse_shmem(struct mm_struct *mm,
> radix_tree_replace_slot(slot,
> new_page + (index % HPAGE_PMD_NR));
>
> + slot = radix_tree_iter_next(&iter);
> index++;
> continue;
> out_lru:
> @@ -1535,6 +1539,7 @@ static void collapse_shmem(struct mm_struct *mm,
> putback_lru_page(page);
> unlock_page(page);
> spin_lock_irq(&mapping->tree_lock);
> + slot = radix_tree_iter_next(&iter);
> }
> VM_BUG_ON(nr_none);
> spin_unlock_irq(&mapping->tree_lock);
> --
> 2.10.2
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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