On Fri, 9 Sep 2016 15:38:38 -0700 Santosh Shilimkar <santosh.shilimkar@xxxxxxxxxx> wrote:
> 'commit 62c230bc1790 ("mm: add support for a filesystem to activate swap
> files and use direct_IO for writing swap pages")' replaced swap_aops
> dirty hook from __set_page_dirty_no_writeback() to swap_set_page_dirty().
> As such for normal cases without these special SWP flags
> code path falls back to __set_page_dirty_no_writeback()
> so behaviour is expected to be same as before.
>
> But swap_set_page_dirty() makes use of helper page_swap_info() to
> get sis(swap_info_struct) to check for the flags like SWP_FILE,
> SWP_BLKDEV etc as desired for those features. This helper has
> BUG_ON(!PageSwapCache(page)) which is racy and safe only for
> set_page_dirty_lock() path. For set_page_dirty() path which is
> often needed for cases to be called from irq context, kswapd()
> can togele the flag behind the back while the call is
> getting executed when system is low on memory and heavy
> swapping is ongoing.
>
> This ends up with undesired kernel panic. Patch just moves
> the check outside the helper to its users appropriately
> to fix kernel panic for the described path. Couple
> of users of helpers already take care of SwapCache
> condition so I skipped them.
>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Joe Perches <joe@xxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
I'll add
Cc: <stable@xxxxxxxxxxxxxxx> [4.7.x]
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -264,6 +264,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
> int ret;
> struct swap_info_struct *sis = page_swap_info(page);
>
> + BUG_ON(!PageSwapCache(page));
> if (sis->flags & SWP_FILE) {
> struct kiocb kiocb;
> struct file *swap_file = sis->swap_file;
> @@ -337,6 +338,7 @@ int swap_readpage(struct page *page)
> int ret = 0;
> struct swap_info_struct *sis = page_swap_info(page);
>
> + BUG_ON(!PageSwapCache(page));
> VM_BUG_ON_PAGE(!PageLocked(page), page);
> VM_BUG_ON_PAGE(PageUptodate(page), page);
> if (frontswap_load(page) == 0) {
> @@ -386,6 +388,7 @@ int swap_set_page_dirty(struct page *page)
>
> if (sis->flags & SWP_FILE) {
> struct address_space *mapping = sis->swap_file->f_mapping;
> + BUG_ON(!PageSwapCache(page));
> return mapping->a_ops->set_page_dirty(page);
> } else {
> return __set_page_dirty_no_writeback(page);
I guess this is OK for 4.8 but for later kernels, let's quieten it down
a bit?
From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: mm/page_io.c: replace some BUG_ON()s with VM_BUG_ON_PAGE()
So they are CONFIG_DEBUG_VM-only and more informative.
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxx>
Cc: Joe Perches <joe@xxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Santosh Shilimkar <santosh.shilimkar@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_io.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff -puN mm/page_io.c~mm-fix-the-page_swap_info-bug_on-check-fix mm/page_io.c
--- a/mm/page_io.c~mm-fix-the-page_swap_info-bug_on-check-fix
+++ a/mm/page_io.c
@@ -264,7 +264,7 @@ int __swap_writepage(struct page *page,
int ret;
struct swap_info_struct *sis = page_swap_info(page);
- BUG_ON(!PageSwapCache(page));
+ VM_BUG_ON_PAGE(!PageSwapCache(page), page);
if (sis->flags & SWP_FILE) {
struct kiocb kiocb;
struct file *swap_file = sis->swap_file;
@@ -338,7 +338,7 @@ int swap_readpage(struct page *page)
int ret = 0;
struct swap_info_struct *sis = page_swap_info(page);
- BUG_ON(!PageSwapCache(page));
+ VM_BUG_ON_PAGE(!PageSwapCache(page), page);
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(PageUptodate(page), page);
if (frontswap_load(page) == 0) {
@@ -388,7 +388,8 @@ int swap_set_page_dirty(struct page *pag
if (sis->flags & SWP_FILE) {
struct address_space *mapping = sis->swap_file->f_mapping;
- BUG_ON(!PageSwapCache(page));
+
+ VM_BUG_ON_PAGE(!PageSwapCache(page), page);
return mapping->a_ops->set_page_dirty(page);
} else {
return __set_page_dirty_no_writeback(page);
diff -puN mm/swapfile.c~mm-fix-the-page_swap_info-bug_on-check-fix mm/swapfile.c
_
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