From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f67.google.com ([209.85.208.67]:44085 "EHLO mail-ed1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727640AbeINVL7 (ORCPT ); Fri, 14 Sep 2018 17:11:59 -0400 Received: by mail-ed1-f67.google.com with SMTP id s10-v6so7816092edb.11 for ; Fri, 14 Sep 2018 08:56:51 -0700 (PDT) Message-ID: <1536940609.3185.29.camel@arista.com> Subject: Re: [LKP] [tty] f26eb68a52: INFO:task_blocked_for_more_than#seconds From: Dmitry Safonov To: kernel test robot Cc: linux-kernel@vger.kernel.org, Dmitry Safonov <0x7f454c46@gmail.com>, Daniel Axtens , Dmitry Vyukov , Mark Rutland , Michael Neuling , Mikulas Patocka , Nathan March , Pasi =?ISO-8859-1?Q?K=E4rkk=E4inen?= , Peter Hurley , Peter Zijlstra , Sergey Senozhatsky , Tan Xiaojun , Tetsuo Handa , Jiri Slaby , syzbot+3aa9784721dfb90e984d@syzkaller.appspotmail.com, stable@vger.kernel.org, Greg Kroah-Hartman , Jiri Slaby , lkp@01.org Date: Fri, 14 Sep 2018 16:56:49 +0100 In-Reply-To: <20180914090151.GH7632@shao2-debian> References: <20180914090151.GH7632@shao2-debian> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org List-ID: On Fri, 2018-09-14 at 17:01 +0800, kernel test robot wrote: > FYI, we noticed the following commit (built with gcc-4.9): Thanks, [..] > [ 245.080051] INFO: task lkp-setup-rootf:500 blocked for more than > 120 seconds. > [ 245.082850] Tainted: G W T 4.19.0-rc3-00014- > gf26eb68 #1 > [ 245.084673] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" > disables this message. > [ 245.086455] lkp-setup-rootf D 6516 500 498 0x00000000 > [ 245.087766] Call Trace: > [ 245.088391] __schedule+0x4b1/0xe80 > [ 245.089322] schedule+0x25/0x60 > [ 245.090178] schedule_timeout+0x275/0x4e0 > [ 245.091105] ? __ldsem_down_write_nested+0x1aa/0x300 > [ 245.092217] __ldsem_down_write_nested+0x1b2/0x300 > [ 245.093286] ? ldsem_down_write+0x2a/0x2e > [ 245.094305] ldsem_down_write+0x2a/0x2e > [ 245.095211] tty_ldisc_lock+0x16/0x40 > [ 245.096104] tty_reopen+0x3f/0xc0 > [ 245.096892] tty_open+0x3cf/0x450 > [ 245.097718] chrdev_open+0x9c/0x1f0 > [ 245.098511] ? security_file_open+0x99/0xa0 > [ 245.099512] do_dentry_open+0x3d5/0x5d0 > [ 245.100428] ? inode_permission+0x95/0x180 > [ 245.101351] ? cdev_put+0x30/0x30 > [ 245.102138] vfs_open+0x2d/0x30 > [ 245.102898] path_openat+0x9e1/0x17d0 > [ 245.103733] do_filp_open+0x6a/0x120 > [ 245.104541] ? _raw_spin_unlock+0x22/0x30 > [ 245.105439] ? __alloc_fd+0xa5/0x170 > [ 245.106309] do_sys_open+0x13a/0x250 > [ 245.107118] sys_open+0x22/0x30 > [ 245.107980] do_int80_syscall_32+0x94/0x1c0 > [ 245.108982] entry_INT80_32+0xf3/0xf3 So, unfortunately, I'll still have to set timeout to 5 sec for tty_reopen(). The better fix would be to release read lock whenever a writer is pending (say n_tty_receive_buf_common() can fallback), but that's probably better to put in another patches set, as this one is already packed. Annoyingly, it means that open(tty) will have now more chances to fail then before.. But still it's better than a panic with null-ptr deref. -- Thanks, Dmitry