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ksm: swap the two output parameters of chain/chain_prune

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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: Andrea Arcangeli <aarcange@redhat.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Tested-by: Dan 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrea Arcangeli 2017-07-06 15:37:05 -07:00 committed by Linus Torvalds
parent 0ba1d0f7c4
commit 8dc5ffcd5a
1 changed files with 52 additions and 26 deletions
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78
mm/ksm.c
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@ -1313,14 +1313,14 @@ bool is_page_sharing_candidate(struct stable_node *stable_node)
return __is_page_sharing_candidate(stable_node, 0); return __is_page_sharing_candidate(stable_node, 0);
} }
static struct stable_node *stable_node_dup(struct stable_node **_stable_node, struct page *stable_node_dup(struct stable_node **_stable_node_dup,
struct page **tree_page, struct stable_node **_stable_node,
struct rb_root *root, struct rb_root *root,
bool prune_stale_stable_nodes) bool prune_stale_stable_nodes)
{ {
struct stable_node *dup, *found = NULL, *stable_node = *_stable_node; struct stable_node *dup, *found = NULL, *stable_node = *_stable_node;
struct hlist_node *hlist_safe; struct hlist_node *hlist_safe;
struct page *_tree_page; struct page *_tree_page, *tree_page = NULL;
int nr = 0; int nr = 0;
int found_rmap_hlist_len; int found_rmap_hlist_len;
@ -1353,14 +1353,14 @@ static struct stable_node *stable_node_dup(struct stable_node **_stable_node,
if (!found || if (!found ||
dup->rmap_hlist_len > found_rmap_hlist_len) { dup->rmap_hlist_len > found_rmap_hlist_len) {
if (found) if (found)
put_page(*tree_page); put_page(tree_page);
found = dup; found = dup;
found_rmap_hlist_len = found->rmap_hlist_len; 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) if (!prune_stale_stable_nodes)
break; break;
/* skip put_page */
continue; 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, 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); 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
struct rb_root *root, * *_stable_node_dup if the returned tree_page is NULL.
bool prune_stale_stable_nodes) *
* 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; struct stable_node *stable_node = *_stable_node;
if (!is_stable_node_chain(stable_node)) { if (!is_stable_node_chain(stable_node)) {
if (is_page_sharing_candidate(stable_node)) { if (is_page_sharing_candidate(stable_node)) {
*tree_page = get_ksm_page(stable_node, false); *_stable_node_dup = stable_node;
return 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 NULL;
} }
return stable_node_dup(_stable_node, tree_page, root, return stable_node_dup(_stable_node_dup, _stable_node, root,
prune_stale_stable_nodes); prune_stale_stable_nodes);
} }
static __always_inline struct stable_node *chain_prune(struct stable_node **s_n, static __always_inline struct page *chain_prune(struct stable_node **s_n_d,
struct page **t_p, struct stable_node **s_n,
struct rb_root *root) 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, static __always_inline struct page *chain(struct stable_node **s_n_d,
struct page **t_p, struct stable_node *s_n,
struct rb_root *root) 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(); cond_resched();
stable_node = rb_entry(*new, struct stable_node, node); stable_node = rb_entry(*new, struct stable_node, node);
stable_node_any = NULL; 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 * NOTE: stable_node may have been freed by
* chain_prune() if the returned stable_node_dup is * 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(); cond_resched();
stable_node = rb_entry(*new, struct stable_node, node); stable_node = rb_entry(*new, struct stable_node, node);
stable_node_any = NULL; 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) { if (!stable_node_dup) {
/* /*
* Either all stable_node dups were full in * Either all stable_node dups were full in