diff options
| -rw-r--r-- | mm/shmem.c | 57 |
1 files changed, 37 insertions, 20 deletions
diff --git a/mm/shmem.c b/mm/shmem.c index 585bd220a21e..a15a466d0d1d 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -683,10 +683,21 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, mutex_lock(&shmem_swaplist_mutex); /* * We needed to drop mutex to make that restrictive page - * allocation; but the inode might already be freed by now, - * and we cannot refer to inode or mapping or info to check. - * However, we do hold page lock on the PageSwapCache page, - * so can check if that still has our reference remaining. + * allocation, but the inode might have been freed while we + * dropped it: although a racing shmem_evict_inode() cannot + * complete without emptying the radix_tree, our page lock + * on this swapcache page is not enough to prevent that - + * free_swap_and_cache() of our swap entry will only + * trylock_page(), removing swap from radix_tree whatever. + * + * We must not proceed to shmem_add_to_page_cache() if the + * inode has been freed, but of course we cannot rely on + * inode or mapping or info to check that. However, we can + * safely check if our swap entry is still in use (and here + * it can't have got reused for another page): if it's still + * in use, then the inode cannot have been freed yet, and we + * can safely proceed (if it's no longer in use, that tells + * nothing about the inode, but we don't need to unuse swap). */ if (!page_swapcount(*pagep)) error = -ENOENT; @@ -730,9 +741,9 @@ int shmem_unuse(swp_entry_t swap, struct page *page) /* * There's a faint possibility that swap page was replaced before - * caller locked it: it will come back later with the right page. + * caller locked it: caller will come back later with the right page. */ - if (unlikely(!PageSwapCache(page))) + if (unlikely(!PageSwapCache(page) || page_private(page) != swap.val)) goto out; /* @@ -995,21 +1006,15 @@ static int shmem_replace_page(struct page **pagep, gfp_t gfp, newpage = shmem_alloc_page(gfp, info, index); if (!newpage) return -ENOMEM; - VM_BUG_ON(shmem_should_replace_page(newpage, gfp)); - *pagep = newpage; page_cache_get(newpage); copy_highpage(newpage, oldpage); + flush_dcache_page(newpage); - VM_BUG_ON(!PageLocked(oldpage)); __set_page_locked(newpage); - VM_BUG_ON(!PageUptodate(oldpage)); SetPageUptodate(newpage); - VM_BUG_ON(!PageSwapBacked(oldpage)); SetPageSwapBacked(newpage); - VM_BUG_ON(!swap_index); set_page_private(newpage, swap_index); - VM_BUG_ON(!PageSwapCache(oldpage)); SetPageSwapCache(newpage); /* @@ -1019,13 +1024,24 @@ static int shmem_replace_page(struct page **pagep, gfp_t gfp, spin_lock_irq(&swap_mapping->tree_lock); error = shmem_radix_tree_replace(swap_mapping, swap_index, oldpage, newpage); - __inc_zone_page_state(newpage, NR_FILE_PAGES); - __dec_zone_page_state(oldpage, NR_FILE_PAGES); + if (!error) { + __inc_zone_page_state(newpage, NR_FILE_PAGES); + __dec_zone_page_state(oldpage, NR_FILE_PAGES); + } spin_unlock_irq(&swap_mapping->tree_lock); - BUG_ON(error); - mem_cgroup_replace_page_cache(oldpage, newpage); - lru_cache_add_anon(newpage); + if (unlikely(error)) { + /* + * Is this possible? I think not, now that our callers check + * both PageSwapCache and page_private after getting page lock; + * but be defensive. Reverse old to newpage for clear and free. + */ + oldpage = newpage; + } else { + mem_cgroup_replace_page_cache(oldpage, newpage); + lru_cache_add_anon(newpage); + *pagep = newpage; + } ClearPageSwapCache(oldpage); set_page_private(oldpage, 0); @@ -1033,7 +1049,7 @@ static int shmem_replace_page(struct page **pagep, gfp_t gfp, unlock_page(oldpage); page_cache_release(oldpage); page_cache_release(oldpage); - return 0; + return error; } /* @@ -1107,7 +1123,8 @@ repeat: /* We have to do this with page locked to prevent races */ lock_page(page); - if (!PageSwapCache(page) || page->mapping) { + if (!PageSwapCache(page) || page_private(page) != swap.val || + page->mapping) { error = -EEXIST; /* try again */ goto failed; } |