2020-01-11 09:44:41

by Zhihao Cheng

Subject: [PATCH v2] ubifs: Fix deadlock in concurrent bulk-read and writepage

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 <[email protected]>
Suggested-by: zhangyi (F) <[email protected]>
Cc: <[email protected]>
Fixes: 4793e7c5e1c ("UBIFS: add bulk-read facility")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206153
---
fs/ubifs/file.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index cd52585..c649048 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -786,7 +786,9 @@ static int ubifs_do_bulk_read(struct ubifs_info *c, struct bu_info *bu,

if (page_offset > end_index)
break;
- page = find_or_create_page(mapping, page_offset, ra_gfp_mask);
+ page = pagecache_get_page(mapping, page_offset,
+ FGP_LOCK|FGP_ACCESSED|FGP_CREAT|FGP_NOWAIT,
+ ra_gfp_mask);
if (!page)
break;
if (!PageUptodate(page))
--
2.7.4

2020-01-17 00:26:21

by Richard Weinberger

Subject: Re: [PATCH v2] ubifs: Fix deadlock in concurrent bulk-read and writepage

On Sat, Jan 11, 2020 at 10:43 AM Zhihao Cheng <[email protected]> wrote:
>
> 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 <[email protected]>
> Suggested-by: zhangyi (F) <[email protected]>
> Cc: <[email protected]>
> Fixes: 4793e7c5e1c ("UBIFS: add bulk-read facility")
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206153
> ---
> fs/ubifs/file.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)

Applied. Thanks a lot for hunting this down!

--
Thanks,
//richard