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-rw-r--r--include/linux/ksm.h20
-rw-r--r--mm/ksm.c3
-rw-r--r--mm/memory.c39
3 files changed, 43 insertions, 19 deletions
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 74d691e..3319a69 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -16,6 +16,9 @@
struct stable_node;
struct mem_cgroup;
+struct page *ksm_does_need_to_copy(struct page *page,
+ struct vm_area_struct *vma, unsigned long address);
+
#ifdef CONFIG_KSM
int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
unsigned long end, int advice, unsigned long *vm_flags);
@@ -70,19 +73,14 @@ static inline void set_page_stable_node(struct page *page,
* We'd like to make this conditional on vma->vm_flags & VM_MERGEABLE,
* but what if the vma was unmerged while the page was swapped out?
*/
-struct page *ksm_does_need_to_copy(struct page *page,
- struct vm_area_struct *vma, unsigned long address);
-static inline struct page *ksm_might_need_to_copy(struct page *page,
+static inline int ksm_might_need_to_copy(struct page *page,
struct vm_area_struct *vma, unsigned long address)
{
struct anon_vma *anon_vma = page_anon_vma(page);
- if (!anon_vma ||
- (anon_vma->root == vma->anon_vma->root &&
- page->index == linear_page_index(vma, address)))
- return page;
-
- return ksm_does_need_to_copy(page, vma, address);
+ return anon_vma &&
+ (anon_vma->root != vma->anon_vma->root ||
+ page->index != linear_page_index(vma, address));
}
int page_referenced_ksm(struct page *page,
@@ -115,10 +113,10 @@ static inline int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
return 0;
}
-static inline struct page *ksm_might_need_to_copy(struct page *page,
+static inline int ksm_might_need_to_copy(struct page *page,
struct vm_area_struct *vma, unsigned long address)
{
- return page;
+ return 0;
}
static inline int page_referenced_ksm(struct page *page,
diff --git a/mm/ksm.c b/mm/ksm.c
index e2ae004..b1873cf 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1504,8 +1504,6 @@ struct page *ksm_does_need_to_copy(struct page *page,
{
struct page *new_page;
- unlock_page(page); /* any racers will COW it, not modify it */
-
new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
if (new_page) {
copy_user_highpage(new_page, page, address, vma);
@@ -1521,7 +1519,6 @@ struct page *ksm_does_need_to_copy(struct page *page,
add_page_to_unevictable_list(new_page);
}
- page_cache_release(page);
return new_page;
}
diff --git a/mm/memory.c b/mm/memory.c
index 6b2ab10..71b161b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2623,7 +2623,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned int flags, pte_t orig_pte)
{
spinlock_t *ptl;
- struct page *page;
+ struct page *page, *swapcache = NULL;
swp_entry_t entry;
pte_t pte;
struct mem_cgroup *ptr = NULL;
@@ -2679,10 +2679,23 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
lock_page(page);
delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
- page = ksm_might_need_to_copy(page, vma, address);
- if (!page) {
- ret = VM_FAULT_OOM;
- goto out;
+ /*
+ * Make sure try_to_free_swap didn't release the swapcache
+ * from under us. The page pin isn't enough to prevent that.
+ */
+ if (unlikely(!PageSwapCache(page)))
+ goto out_page;
+
+ if (ksm_might_need_to_copy(page, vma, address)) {
+ swapcache = page;
+ page = ksm_does_need_to_copy(page, vma, address);
+
+ if (unlikely(!page)) {
+ ret = VM_FAULT_OOM;
+ page = swapcache;
+ swapcache = NULL;
+ goto out_page;
+ }
}
if (mem_cgroup_try_charge_swapin(mm, page, GFP_KERNEL, &ptr)) {
@@ -2735,6 +2748,18 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
try_to_free_swap(page);
unlock_page(page);
+ if (swapcache) {
+ /*
+ * Hold the lock to avoid the swap entry to be reused
+ * until we take the PT lock for the pte_same() check
+ * (to avoid false positives from pte_same). For
+ * further safety release the lock after the swap_free
+ * so that the swap count won't change under a
+ * parallel locked swapcache.
+ */
+ unlock_page(swapcache);
+ page_cache_release(swapcache);
+ }
if (flags & FAULT_FLAG_WRITE) {
ret |= do_wp_page(mm, vma, address, page_table, pmd, ptl, pte);
@@ -2756,6 +2781,10 @@ out_page:
unlock_page(page);
out_release:
page_cache_release(page);
+ if (swapcache) {
+ unlock_page(swapcache);
+ page_cache_release(swapcache);
+ }
return ret;
}
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