From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6E0F0C433F5 for ; Mon, 20 Dec 2021 15:03:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238481AbhLTPDM (ORCPT ); Mon, 20 Dec 2021 10:03:12 -0500 Received: from dfw.source.kernel.org ([139.178.84.217]:46056 "EHLO dfw.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239815AbhLTO7N (ORCPT ); Mon, 20 Dec 2021 09:59:13 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id F02EA6118E; Mon, 20 Dec 2021 14:59:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D41A7C36AE9; Mon, 20 Dec 2021 14:59:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1640012351; bh=hwTfC7fKmk+YvCuDekklJf8Xz3A0K0JD9UWGtfF7KXA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bTqSDhuoAzb5Vr32C5pCKTMZRnChBy6mWEVd/sIE91go1Iwy8K4FGwVCL9cCYGhgY yrLuFHE3/iSA+JIB/UUTtPomBbysXOURzJTBmLaI37yBvz0V+ZsNEA9nCb7GBnzv2I UTTnF7rLDJqo4/xeEUF90GQ6OSov8wNTencL8MJo= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot+b18b8be69df33a3918e9@syzkaller.appspotmail.com, Jens Axboe Subject: [PATCH 5.15 169/177] io-wq: drop wqe lock before creating new worker Date: Mon, 20 Dec 2021 15:35:19 +0100 Message-Id: <20211220143045.761836051@linuxfoundation.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20211220143040.058287525@linuxfoundation.org> References: <20211220143040.058287525@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jens Axboe 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: __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 Signed-off-by: Greg Kroah-Hartman --- 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); } }