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-rw-r--r--mm/memory.c41
1 files changed, 36 insertions, 5 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 6b2ab10..0e18b4d 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 +2679,25 @@ 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 or reuse_swap_page or swapoff did not
+ * release the swapcache from under us. The page pin, and pte_same
+ * test below, are not enough to exclude that. Even if it is still
+ * swapcache, we need to check that the page's swap has not changed.
+ */
+ if (unlikely(!PageSwapCache(page) || page_private(page) != entry.val))
+ 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 +2750,18 @@ 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 +2783,10 @@ out_page:
unlock_page(page);
out_release:
page_cache_release(page);
+ if (swapcache) {
+ unlock_page(swapcache);
+ page_cache_release(swapcache);
+ }
return ret;
}