From: Jens Axboe axboe@kernel.dk
commit d800c65c2d4eccebb27ffb7808e842d5b533823c upstream.
We have two io-wq creation paths:
- On queue enqueue - When a worker goes to sleep
The latter invokes worker creation with the wqe->lock held, but that can run into problems if we end up exiting and need to cancel the queued work. syzbot caught this:
============================================ WARNING: possible recursive locking detected 5.16.0-rc4-syzkaller #0 Not tainted -------------------------------------------- iou-wrk-6468/6471 is trying to acquire lock: ffff88801aa98018 (&wqe->lock){+.+.}-{2:2}, at: io_worker_cancel_cb+0xb7/0x210 fs/io-wq.c:187
but task is already holding lock: ffff88801aa98018 (&wqe->lock){+.+.}-{2:2}, at: io_wq_worker_sleeping+0xb6/0x140 fs/io-wq.c:700
other info that might help us debug this: Possible unsafe locking scenario:
CPU0 ---- lock(&wqe->lock); lock(&wqe->lock);
*** DEADLOCK ***
May be due to missing lock nesting notation
1 lock held by iou-wrk-6468/6471: #0: ffff88801aa98018 (&wqe->lock){+.+.}-{2:2}, at: io_wq_worker_sleeping+0xb6/0x140 fs/io-wq.c:700
stack backtrace: CPU: 1 PID: 6471 Comm: iou-wrk-6468 Not tainted 5.16.0-rc4-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x1dc/0x2d8 lib/dump_stack.c:106 print_deadlock_bug kernel/locking/lockdep.c:2956 [inline] check_deadlock kernel/locking/lockdep.c:2999 [inline] validate_chain+0x5984/0x8240 kernel/locking/lockdep.c:3788 __lock_acquire+0x1382/0x2b00 kernel/locking/lockdep.c:5027 lock_acquire+0x19f/0x4d0 kernel/locking/lockdep.c:5637 __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline] _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:154 io_worker_cancel_cb+0xb7/0x210 fs/io-wq.c:187 io_wq_cancel_tw_create fs/io-wq.c:1220 [inline] io_queue_worker_create+0x3cf/0x4c0 fs/io-wq.c:372 io_wq_worker_sleeping+0xbe/0x140 fs/io-wq.c:701 sched_submit_work kernel/sched/core.c:6295 [inline] schedule+0x67/0x1f0 kernel/sched/core.c:6323 schedule_timeout+0xac/0x300 kernel/time/timer.c:1857 wait_woken+0xca/0x1b0 kernel/sched/wait.c:460 unix_msg_wait_data net/unix/unix_bpf.c:32 [inline] unix_bpf_recvmsg+0x7f9/0xe20 net/unix/unix_bpf.c:77 unix_stream_recvmsg+0x214/0x2c0 net/unix/af_unix.c:2832 sock_recvmsg_nosec net/socket.c:944 [inline] sock_recvmsg net/socket.c:962 [inline] sock_read_iter+0x3a7/0x4d0 net/socket.c:1035 call_read_iter include/linux/fs.h:2156 [inline] io_iter_do_read fs/io_uring.c:3501 [inline] io_read fs/io_uring.c:3558 [inline] io_issue_sqe+0x144c/0x9590 fs/io_uring.c:6671 io_wq_submit_work+0x2d8/0x790 fs/io_uring.c:6836 io_worker_handle_work+0x808/0xdd0 fs/io-wq.c:574 io_wqe_worker+0x395/0x870 fs/io-wq.c:630 ret_from_fork+0x1f/0x30
We can safely drop the lock before doing work creation, making the two contexts the same in that regard.
Reported-by: syzbot+b18b8be69df33a3918e9@syzkaller.appspotmail.com Fixes: 71a85387546e ("io-wq: check for wq exit after adding new worker task_work") Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/io-wq.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/fs/io-wq.c +++ b/fs/io-wq.c @@ -395,7 +395,9 @@ static void io_wqe_dec_running(struct io if (atomic_dec_and_test(&acct->nr_running) && io_acct_run_queue(acct)) { atomic_inc(&acct->nr_running); atomic_inc(&wqe->wq->worker_refs); + raw_spin_unlock(&wqe->lock); io_queue_worker_create(worker, acct, create_worker_cb); + raw_spin_lock(&wqe->lock); } }