[PATCH 3.16 53/99] ubifs: Fix deadlock in concurrent bulk-read and writepage

[Ben Hutchings]

3.16.84-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>

commit f5de5b83303e61b1f3fb09bd77ce3ac2d7a475f2 upstream.

In ubifs, concurrent execution of writepage and bulk read on the same file
may cause ABBA deadlock, for example (Reproduce method see Link):

Process A(Bulk-read starts from page4)         Process B(write page4 back)
  vfs_read                                       wb_workfn or fsync
  ...                                            ...
  generic_file_buffered_read                     write_cache_pages
    ubifs_readpage                                 LOCK(page4)

      ubifs_bulk_read                              ubifs_writepage
        LOCK(ui->ui_mutex)                           ubifs_write_inode

	  ubifs_do_bulk_read                           LOCK(ui->ui_mutex)
	    find_or_create_page(alloc page4)                  â
	      LOCK(page4)                   <--     ABBA deadlock occurs!

In order to ensure the serialization execution of bulk read, we can't
remove the big lock 'ui->ui_mutex' in ubifs_bulk_read(). Instead, we
allow ubifs_do_bulk_read() to lock page failed by replacing
find_or_create_page(FGP_LOCK) with
pagecache_get_page(FGP_LOCK | FGP_NOWAIT).

Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
Suggested-by: zhangyi (F) <yi.zhang@xxxxxxxxxx>
Fixes: 4793e7c5e1c ("UBIFS: add bulk-read facility")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206153
Signed-off-by: Richard Weinberger <richard@xxxxxx>
[bwh: Backported to 3.16: Keep using constant GFP flags parameter.]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/ubifs/file.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -782,8 +782,9 @@ static int ubifs_do_bulk_read(struct ubi
 
 		if (page_offset > end_index)
 			break;
-		page = find_or_create_page(mapping, page_offset,
-					   GFP_NOFS | __GFP_COLD);
+		page = pagecache_get_page(mapping, page_offset,
+				 FGP_LOCK|FGP_ACCESSED|FGP_CREAT|FGP_NOWAIT,
+				 GFP_NOFS | __GFP_COLD);
 		if (!page)
 			break;
 		if (!PageUptodate(page))