[PATCH 4.4] ubifs: Fix deadlock in concurrent bulk-read and writepage

From: Zhihao Cheng
Date: Mon Feb 17 2020 - 07:17:26 EST

[ Upstream commit f5de5b83303e61b1f3fb09bd77ce3ac2d7a475f2 ]

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>
Cc: <Stable@xxxxxxxxxxxxxxx>
Fixes: 4793e7c5e1c ("UBIFS: add bulk-read facility")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206153
Signed-off-by: Richard Weinberger <richard@xxxxxx>
fs/ubifs/file.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index b895af7d8d80..e6d0a7df341d 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -782,8 +782,9 @@ static int ubifs_do_bulk_read(struct ubifs_info *c, struct bu_info *bu,

if (page_offset > end_index)
- page = find_or_create_page(mapping, page_offset,
+ page = pagecache_get_page(mapping, page_offset,
if (!page)
if (!PageUptodate(page))