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Commit b936887e authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
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mm: workingset: turn shadow node shrinker bugs into warnings 

When the shadow page shrinker tries to reclaim a radix tree node but
finds it in an unexpected state - it should contain no pages, and
non-zero shadow entries - there is no need to kill the executing task or
even the entire system.  Warn about the invalid state, then leave that
tree node be.  Simply don't put it back on the shadow LRU for future
reclaim and move on.

Link: http://lkml.kernel.org/r/20161117191138.22769-4-hannes@cmpxchg.org


Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <mawilcox@linuxonhyperv.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 59749e6c

mm/workingset.c

+12 −8
Original line number Diff line number Diff line
@@ -418,23 +418,27 @@ static enum lru_status shadow_lru_isolate(struct list_head *item, 
	 * no pages, so we expect to be able to remove them all and

	 * delete and free the empty node afterwards.

	 */

	BUG_ON(!workingset_node_shadows(node));

	BUG_ON(workingset_node_pages(node));



	if (WARN_ON_ONCE(!workingset_node_shadows(node)))

		goto out_invalid;

	if (WARN_ON_ONCE(workingset_node_pages(node)))

		goto out_invalid;

	for (i = 0; i < RADIX_TREE_MAP_SIZE; i++) {

		if (node->slots[i]) {

			BUG_ON(!radix_tree_exceptional_entry(node->slots[i]));

			if (WARN_ON_ONCE(!radix_tree_exceptional_entry(node->slots[i])))

				goto out_invalid;

			if (WARN_ON_ONCE(!mapping->nrexceptional))

				goto out_invalid;

			node->slots[i] = NULL;

			workingset_node_shadows_dec(node);

			BUG_ON(!mapping->nrexceptional);

			mapping->nrexceptional--;

		}

	}

	BUG_ON(workingset_node_shadows(node));

	if (WARN_ON_ONCE(workingset_node_shadows(node)))

		goto out_invalid;

	inc_node_state(page_pgdat(virt_to_page(node)), WORKINGSET_NODERECLAIM);

	if (!__radix_tree_delete_node(&mapping->page_tree, node))

		BUG();

	__radix_tree_delete_node(&mapping->page_tree, node);



out_invalid:

	spin_unlock(&mapping->tree_lock);

	ret = LRU_REMOVED_RETRY;

out: