swap: fix swapfile read/write offset

We're not factoring in the start of the file for where to write and
read the swapfile, which leads to very unfortunate side effects of
writing where we should not be...

Fixes: 48d15436fde6 ("mm: remove get_swap_bio")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 32f665b1ee85c2b675ab2967f68e314007b90f6e..4cc6ec3bf0abbff65eff0293552eb1099892dd26 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -485,6 +485,7 @@ struct backing_dev_info;
 extern int init_swap_address_space(unsigned int type, unsigned long nr_pages);
 extern void exit_swap_address_space(unsigned int type);
 extern struct swap_info_struct *get_swap_device(swp_entry_t entry);
+sector_t swap_page_sector(struct page *page);
 
 static inline void put_swap_device(struct swap_info_struct *si)
 {

diff --git a/mm/page_io.c b/mm/page_io.c
index 485fa5cca4a29b554bac817b8d31a15329f8f4d8..c493ce9ebcf50760e8717784d5eb465de3ddf7e8 100644 (file)
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -254,11 +254,6 @@ out:
        return ret;
 }
 
-static sector_t swap_page_sector(struct page *page)
-{
-       return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9);
-}
-
 static inline void count_swpout_vm_event(struct page *page)
 {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE

diff --git a/mm/swapfile.c b/mm/swapfile.c
index f039745989d22617b1287f0e6ac84ce8a10d0c55..084a5b9a18e5c36b031809769482781c1f7a60ff 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -219,6 +219,19 @@ offset_to_swap_extent(struct swap_info_struct *sis, unsigned long offset)
        BUG();
 }
 
+sector_t swap_page_sector(struct page *page)
+{
+       struct swap_info_struct *sis = page_swap_info(page);
+       struct swap_extent *se;
+       sector_t sector;
+       pgoff_t offset;
+
+       offset = __page_file_index(page);
+       se = offset_to_swap_extent(sis, offset);
+       sector = se->start_block + (offset - se->start_page);
+       return sector << (PAGE_SHIFT - 9);
+}
+
 /*
  * swap allocation tell device that a cluster of swap can now be discarded,
  * to allow the swap device to optimize its wear-levelling.