On Wed, Dec 09, 2015 at 12:44:34PM +0300, Andrey Ryabinin wrote:
> tcache_invalidate_node_pages() temporarly drops/takes back node->tree_lock.
> Once lock was dropped, we can't continue iterating to the next slot, because
> another thread might remove and free it. If lock was dropped tree iteration
> has to be restarted.
> Wit this patch we also drop the lock iff we need to resched the task.
>
> https://jira.sw.ru/browse/PSBM-42104
>
> Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com>
> ---
> mm/tcache.c | 23 +++++++++++++++--------
> 1 file changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/mm/tcache.c b/mm/tcache.c
> index b8757cf..a09ae49 100644
> --- a/mm/tcache.c
> +++ b/mm/tcache.c
> @@ -662,6 +662,7 @@ tcache_invalidate_node_pages(struct tcache_node *node)
> struct radix_tree_iter iter;
> struct page *page;
> void **slot;
> + pgoff_t index = 0;
>
> spin_lock_irq(&node->tree_lock);
>
> @@ -674,19 +675,25 @@ tcache_invalidate_node_pages(struct tcache_node *node)
> * Now truncate all pages. Be careful, because pages can still be
> * deleted from this node by the shrinker or by concurrent lookups.
> */
> - radix_tree_for_each_slot(slot, &node->page_tree, &iter, 0) {
> +restart:
> + radix_tree_for_each_slot(slot, &node->page_tree, &iter, index) {
> page = radix_tree_deref_slot_protected(slot, &node->tree_lock);
> BUG_ON(!__tcache_page_tree_delete(node, page->index, page));
> - spin_unlock(&node->tree_lock);
> -
> tcache_lru_del(page);
> put_page(page);
You forgot to update the comment describing the locking rules. Please
do.
>
> - local_irq_enable();
> - cond_resched();
> - local_irq_disable();
> -
> - spin_lock(&node->tree_lock);
> + if (need_resched()) {
> + spin_unlock_irq(&node->tree_lock);
> + cond_resched();
> + spin_lock_irq(&node->tree_lock);
> + /*
> + * Restart iteration over the radix tree, because the
> + * current node could have been freed when we dropped
> + * the lock.
> + */
> + index = page->index + 1;
We released the page, so its ->index might be irrelevant. We must read
it before calling put_page.
> + goto restart;
> + }
> }
>
> BUG_ON(node->nr_pages != 0);
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