[PATCH 4.19 234/338] ubifs: Fix deadlock in concurrent rename whiteout and inode writeback

Greg Kroah-Hartman
2022-04-14T14:03:11Z

From: Zhihao Cheng <chengzhihao1@huawei.com>

commit afd427048047e8efdedab30e8888044e2be5aa9c upstream.

Following hung tasks:
[ 77.028764] task:kworker/u8:4 state:D stack: 0 pid: 132
[ 77.028820] Call Trace:
[ 77.029027] schedule+0x8c/0x1b0
[ 77.029067] mutex_lock+0x50/0x60
[ 77.029074] ubifs_write_inode+0x68/0x1f0 [ubifs]
[ 77.029117] __writeback_single_inode+0x43c/0x570
[ 77.029128] writeback_sb_inodes+0x259/0x740
[ 77.029148] wb_writeback+0x107/0x4d0
[ 77.029163] wb_workfn+0x162/0x7b0

[ 92.390442] task:aa state:D stack: 0 pid: 1506
[ 92.390448] Call Trace:
[ 92.390458] schedule+0x8c/0x1b0
[ 92.390461] wb_wait_for_completion+0x82/0xd0
[ 92.390469] __writeback_inodes_sb_nr+0xb2/0x110
[ 92.390472] writeback_inodes_sb_nr+0x14/0x20
[ 92.390476] ubifs_budget_space+0x705/0xdd0 [ubifs]
[ 92.390503] do_rename.cold+0x7f/0x187 [ubifs]
[ 92.390549] ubifs_rename+0x8b/0x180 [ubifs]
[ 92.390571] vfs_rename+0xdb2/0x1170
[ 92.390580] do_renameat2+0x554/0x770

, are caused by concurrent rename whiteout and inode writeback processes:
rename_whiteout(Thread 1) wb_workfn(Thread2)
ubifs_rename
do_rename
lock_4_inodes (Hold ui_mutex)
ubifs_budget_space
make_free_space
shrink_liability
__writeback_inodes_sb_nr
bdi_split_work_to_wbs (Queue new wb work)
wb_do_writeback(wb work)
__writeback_single_inode
ubifs_write_inode
LOCK(ui_mutex)
↑
wb_wait_for_completion (Wait wb work) <-- deadlock!

Reproducer (Detail program in [Link]):
1. SYS_renameat2("/mp/dir/file", "/mp/dir/whiteout", RENAME_WHITEOUT)
2. Consume out of space before kernel(mdelay) doing budget for whiteout

Fix it by doing whiteout space budget before locking ubifs inodes.
BTW, it also fixes wrong goto tag 'out_release' in whiteout budget
error handling path(It should at least recover dir i_size and unlock
4 ubifs inodes).

Fixes: 9e0a1fff8db56ea ("ubifs: Implement RENAME_WHITEOUT")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=214733
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/ubifs/dir.c | 25 +++++++++++++++----------
1 file changed, 15 insertions(+), 10 deletions(-)

--- a/fs/ubifs/dir.c
+++ b/fs/ubifs/dir.c
@@ -1341,6 +1341,7 @@ static int do_rename(struct inode *old_d

if (flags & RENAME_WHITEOUT) {
union ubifs_dev_desc *dev = NULL;
+ struct ubifs_budget_req wht_req;

dev = kmalloc(sizeof(union ubifs_dev_desc), GFP_NOFS);
if (!dev) {
@@ -1362,6 +1363,20 @@ static int do_rename(struct inode *old_d
whiteout_ui->data = dev;
whiteout_ui->data_len = ubifs_encode_dev(dev, MKDEV(0, 0));
ubifs_assert(c, !whiteout_ui->dirty);
+
+ memset(&wht_req, 0, sizeof(struct ubifs_budget_req));
+ wht_req.dirtied_ino = 1;
+ wht_req.dirtied_ino_d = ALIGN(whiteout_ui->data_len, 8);
+ /*
+ * To avoid deadlock between space budget (holds ui_mutex and
+ * waits wb work) and writeback work(waits ui_mutex), do space
+ * budget before ubifs inodes locked.
+ */
+ err = ubifs_budget_space(c, &wht_req);
+ if (err) {
+ iput(whiteout);
+ goto out_release;
+ }
}

lock_4_inodes(old_dir, new_dir, new_inode, whiteout);
@@ -1436,16 +1451,6 @@ static int do_rename(struct inode *old_d
}

if (whiteout) {
- struct ubifs_budget_req wht_req = { .dirtied_ino = 1,
- .dirtied_ino_d = \
- ALIGN(ubifs_inode(whiteout)->data_len, 8) };
-
- err = ubifs_budget_space(c, &wht_req);
- if (err) {
- iput(whiteout);
- goto out_release;
- }
-
inc_nlink(whiteout);
mark_inode_dirty(whiteout);