| From: Zhihao Cheng <chengzhihao1@huawei.com> |
| Date: Sat, 11 Jan 2020 17:50:36 +0800 |
| Subject: ubifs: Fix deadlock in concurrent bulk-read and writepage |
| MIME-Version: 1.0 |
| Content-Type: text/plain; charset=UTF-8 |
| Content-Transfer-Encoding: 8bit |
| |
| 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@huawei.com> |
| Suggested-by: zhangyi (F) <yi.zhang@huawei.com> |
| Fixes: 4793e7c5e1c ("UBIFS: add bulk-read facility") |
| Link: https://bugzilla.kernel.org/show_bug.cgi?id=206153 |
| Signed-off-by: Richard Weinberger <richard@nod.at> |
| [bwh: Backported to 3.16: Keep using constant GFP flags parameter.] |
| Signed-off-by: Ben Hutchings <ben@decadent.org.uk> |
| --- |
| 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)) |
