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) ↑
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))
