From: Pavel Begunkov <asml.silence@xxxxxxxxx> commit dadebc350da2bef62593b1df007a6e0b90baf42a upstream. WARNING: CPU: 1 PID: 5870 at fs/io_uring.c:5975 io_try_cancel_userdata+0x30f/0x540 fs/io_uring.c:5975 CPU: 0 PID: 5870 Comm: iou-wrk-5860 Not tainted 5.14.0-rc6-next-20210820-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:io_try_cancel_userdata+0x30f/0x540 fs/io_uring.c:5975 Call Trace: io_async_cancel fs/io_uring.c:6014 [inline] io_issue_sqe+0x22d5/0x65a0 fs/io_uring.c:6407 io_wq_submit_work+0x1dc/0x300 fs/io_uring.c:6511 io_worker_handle_work+0xa45/0x1840 fs/io-wq.c:533 io_wqe_worker+0x2cc/0xbb0 fs/io-wq.c:582 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 io_try_cancel_userdata() can be called from io_async_cancel() executing in the io-wq context, so the warning fires, which is there to alert anyone accessing task->io_uring->io_wq in a racy way. However, io_wq_put_and_exit() always first waits for all threads to complete, so the only detail left is to zero tctx->io_wq after the context is removed. note: one little assumption is that when IO_WQ_WORK_CANCEL, the executor won't touch ->io_wq, because io_wq_destroy() might cancel left pending requests in such a way. Cc: stable@xxxxxxxxxxxxxxx Reported-by: syzbot+b0c9d1588ae92866515f@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx> Link: https://lore.kernel.org/r/dfdd37a80cfa9ffd3e59538929c99cdd55d8699e.1629721757.git.asml.silence@xxxxxxxxx Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/io_uring.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -6310,6 +6310,7 @@ static void io_wq_submit_work(struct io_ if (timeout) io_queue_linked_timeout(timeout); + /* either cancelled or io-wq is dying, so don't touch tctx->iowq */ if (work->flags & IO_WQ_WORK_CANCEL) ret = -ECANCELED; @@ -9137,8 +9138,8 @@ static void io_uring_clean_tctx(struct i * Must be after io_uring_del_task_file() (removes nodes under * uring_lock) to avoid race with io_uring_try_cancel_iowq(). */ - tctx->io_wq = NULL; io_wq_put_and_exit(wq); + tctx->io_wq = NULL; } }
