diff --git a/mm/ksm.c b/mm/ksm.c index 5b0894b45ee57257f34bde6072ae63a26c1714e6..cb46fd7890bec7e68184d9d905599860f705bf68 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -666,6 +666,12 @@ static void remove_node_from_stable_tree(struct stable_node *stable_node) free_stable_node(stable_node); } +enum get_ksm_page_flags { + GET_KSM_PAGE_NOLOCK, + GET_KSM_PAGE_LOCK, + GET_KSM_PAGE_TRYLOCK +}; + /* * get_ksm_page: checks if the page indicated by the stable node * is still its ksm page, despite having held no reference to it. @@ -685,7 +691,8 @@ static void remove_node_from_stable_tree(struct stable_node *stable_node) * a page to put something that might look like our key in page->mapping. * is on its way to being freed; but it is an anomaly to bear in mind. */ -static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it) +static struct page *get_ksm_page(struct stable_node *stable_node, + enum get_ksm_page_flags flags) { struct page *page; void *expected_mapping; @@ -727,8 +734,15 @@ static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it) goto stale; } - if (lock_it) { + if (flags == GET_KSM_PAGE_TRYLOCK) { + if (!trylock_page(page)) { + put_page(page); + return ERR_PTR(-EBUSY); + } + } else if (flags == GET_KSM_PAGE_LOCK) lock_page(page); + + if (flags != GET_KSM_PAGE_NOLOCK) { if (READ_ONCE(page->mapping) != expected_mapping) { unlock_page(page); put_page(page); @@ -762,7 +776,7 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) struct page *page; stable_node = rmap_item->head; - page = get_ksm_page(stable_node, true); + page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK); if (!page) goto out; @@ -862,7 +876,7 @@ static int remove_stable_node(struct stable_node *stable_node) struct page *page; int err; - page = get_ksm_page(stable_node, true); + page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK); if (!page) { /* * get_ksm_page did remove_node_from_stable_tree itself. @@ -1387,7 +1401,7 @@ static struct page *stable_node_dup(struct stable_node **_stable_node_dup, * stable_node parameter itself will be freed from * under us if it returns NULL. */ - _tree_page = get_ksm_page(dup, false); + _tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK); if (!_tree_page) continue; nr += 1; @@ -1510,7 +1524,7 @@ static struct page *__stable_node_chain(struct stable_node **_stable_node_dup, if (!is_stable_node_chain(stable_node)) { if (is_page_sharing_candidate(stable_node)) { *_stable_node_dup = stable_node; - return get_ksm_page(stable_node, false); + return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK); } /* * _stable_node_dup set to NULL means the stable_node @@ -1615,7 +1629,8 @@ static struct page *stable_tree_search(struct page *page) * wrprotected at all times. Any will work * fine to continue the walk. */ - tree_page = get_ksm_page(stable_node_any, false); + tree_page = get_ksm_page(stable_node_any, + GET_KSM_PAGE_NOLOCK); } VM_BUG_ON(!stable_node_dup ^ !!stable_node_any); if (!tree_page) { @@ -1675,7 +1690,12 @@ static struct page *stable_tree_search(struct page *page) * It would be more elegant to return stable_node * than kpage, but that involves more changes. */ - tree_page = get_ksm_page(stable_node_dup, true); + tree_page = get_ksm_page(stable_node_dup, + GET_KSM_PAGE_TRYLOCK); + + if (PTR_ERR(tree_page) == -EBUSY) + return ERR_PTR(-EBUSY); + if (unlikely(!tree_page)) /* * The tree may have been rebalanced, @@ -1844,7 +1864,8 @@ static struct stable_node *stable_tree_insert(struct page *kpage) * wrprotected at all times. Any will work * fine to continue the walk. */ - tree_page = get_ksm_page(stable_node_any, false); + tree_page = get_ksm_page(stable_node_any, + GET_KSM_PAGE_NOLOCK); } VM_BUG_ON(!stable_node_dup ^ !!stable_node_any); if (!tree_page) { @@ -2070,6 +2091,9 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) remove_rmap_item_from_tree(rmap_item); if (kpage) { + if (PTR_ERR(kpage) == -EBUSY) + return; + err = try_to_merge_with_ksm_page(rmap_item, page, kpage); if (!err) { /* @@ -2244,7 +2268,8 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page) list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) { - page = get_ksm_page(stable_node, false); + page = get_ksm_page(stable_node, + GET_KSM_PAGE_NOLOCK); if (page) put_page(page); cond_resched();