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Commit 8dc5ffcd authored by Andrea Arcangeli's avatar Andrea Arcangeli Committed by Linus Torvalds
Browse files

ksm: swap the two output parameters of chain/chain_prune 

Some static checker complains if chain/chain_prune returns a potentially
stale pointer.

There are two output parameters to chain/chain_prune, one is tree_page
the other is stable_node_dup.  Like in get_ksm_page the caller has to
check tree_page is NULL before touching the stable_node.  Similarly in
chain/chain_prune the caller has to check tree_page before touching the
stable_node_dup returned or the original stable_node passed as
parameter.

Because the tree_page is never returned as a stale pointer, it may be
more intuitive to return tree_page and to pass stable_node_dup for
reference instead of the reverse.

This patch purely swaps the two output parameters of chain/chain_prune
as a cleanup for the static checker and to mimic the get_ksm_page
behavior more closely.  There's no change to the caller at all except
the swap, it's purely a cleanup and it is a noop from the caller point
of view.

Link: http://lkml.kernel.org/r/20170518173721.22316-3-aarcange@redhat.com


Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
Reported-by: default avatarDan Carpenter <dan.carpenter@oracle.com>
Tested-by: default avatarDan Carpenter <dan.carpenter@oracle.com>
Cc: Evgheni Dereveanchin <ederevea@redhat.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Petr Holasek <pholasek@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Gavin Guo <gavin.guo@canonical.com>
Cc: Jay Vosburgh <jay.vosburgh@canonical.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0ba1d0f7

mm/ksm.c

+52 −26
Original line number Diff line number Diff line
@@ -1313,14 +1313,14 @@ bool is_page_sharing_candidate(struct stable_node *stable_node) 
	return __is_page_sharing_candidate(stable_node, 0);

}



static struct stable_node *stable_node_dup(struct stable_node **_stable_node,

					   struct page **tree_page,

struct page *stable_node_dup(struct stable_node **_stable_node_dup,

			     struct stable_node **_stable_node,

			     struct rb_root *root,

			     bool prune_stale_stable_nodes)

{

	struct stable_node *dup, *found = NULL, *stable_node = *_stable_node;

	struct hlist_node *hlist_safe;

	struct page *_tree_page;

	struct page *_tree_page, *tree_page = NULL;

	int nr = 0;

	int found_rmap_hlist_len;
@@ -1353,14 +1353,14 @@ static struct stable_node *stable_node_dup(struct stable_node **_stable_node, 
			if (!found ||

			    dup->rmap_hlist_len > found_rmap_hlist_len) {

				if (found)

					put_page(*tree_page);

					put_page(tree_page);

				found = dup;

				found_rmap_hlist_len = found->rmap_hlist_len;

				*tree_page = _tree_page;

				tree_page = _tree_page;



				/* skip put_page for found dup */

				if (!prune_stale_stable_nodes)

					break;

				/* skip put_page */

				continue;

			}

		}
@@ -1417,7 +1417,8 @@ static struct stable_node *stable_node_dup(struct stable_node **_stable_node, 
		}

	}



	return found;

	*_stable_node_dup = found;

	return tree_page;

}



static struct stable_node *stable_node_dup_any(struct stable_node *stable_node,
@@ -1433,35 +1434,60 @@ static struct stable_node *stable_node_dup_any(struct stable_node *stable_node, 
			   typeof(*stable_node), hlist_dup);

}



static struct stable_node *__stable_node_chain(struct stable_node **_stable_node,

					       struct page **tree_page,

/*

 * Like for get_ksm_page, this function can free the *_stable_node and

 * *_stable_node_dup if the returned tree_page is NULL.

 *

 * It can also free and overwrite *_stable_node with the found

 * stable_node_dup if the chain is collapsed (in which case

 * *_stable_node will be equal to *_stable_node_dup like if the chain

 * never existed). It's up to the caller to verify tree_page is not

 * NULL before dereferencing *_stable_node or *_stable_node_dup.

 *

 * *_stable_node_dup is really a second output parameter of this

 * function and will be overwritten in all cases, the caller doesn't

 * need to initialize it.

 */

static struct page *__stable_node_chain(struct stable_node **_stable_node_dup,

					struct stable_node **_stable_node,

					struct rb_root *root,

					bool prune_stale_stable_nodes)

{

	struct stable_node *stable_node = *_stable_node;

	if (!is_stable_node_chain(stable_node)) {

		if (is_page_sharing_candidate(stable_node)) {

			*tree_page = get_ksm_page(stable_node, false);

			return stable_node;

			*_stable_node_dup = stable_node;

			return get_ksm_page(stable_node, false);

		}

		/*

		 * _stable_node_dup set to NULL means the stable_node

		 * reached the ksm_max_page_sharing limit.

		 */

		*_stable_node_dup = NULL;

		return NULL;

	}

	return stable_node_dup(_stable_node, tree_page, root,

	return stable_node_dup(_stable_node_dup, _stable_node, root,

			       prune_stale_stable_nodes);

}



static __always_inline struct stable_node *chain_prune(struct stable_node **s_n,

						       struct page **t_p,

static __always_inline struct page *chain_prune(struct stable_node **s_n_d,

						struct stable_node **s_n,

						struct rb_root *root)

{

	return __stable_node_chain(s_n, t_p, root, true);

	return __stable_node_chain(s_n_d, s_n, root, true);

}



static __always_inline struct stable_node *chain(struct stable_node *s_n,

						 struct page **t_p,

static __always_inline struct page *chain(struct stable_node **s_n_d,

					  struct stable_node *s_n,

					  struct rb_root *root)

{

	return __stable_node_chain(&s_n, t_p, root, false);

	struct stable_node *old_stable_node = s_n;

	struct page *tree_page;



	tree_page = __stable_node_chain(s_n_d, &s_n, root, false);

	/* not pruning dups so s_n cannot have changed */

	VM_BUG_ON(s_n != old_stable_node);

	return tree_page;

}



/*
@@ -1502,7 +1528,7 @@ static struct page *stable_tree_search(struct page *page) 
		cond_resched();

		stable_node = rb_entry(*new, struct stable_node, node);

		stable_node_any = NULL;

		stable_node_dup = chain_prune(&stable_node, &tree_page, root);

		tree_page = chain_prune(&stable_node_dup, &stable_node,	root);

		/*

		 * NOTE: stable_node may have been freed by

		 * chain_prune() if the returned stable_node_dup is
@@ -1743,7 +1769,7 @@ static struct stable_node *stable_tree_insert(struct page *kpage) 
		cond_resched();

		stable_node = rb_entry(*new, struct stable_node, node);

		stable_node_any = NULL;

		stable_node_dup = chain(stable_node, &tree_page, root);

		tree_page = chain(&stable_node_dup, stable_node, root);

		if (!stable_node_dup) {

			/*

			 * Either all stable_node dups were full in