Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756167Ab3G3PfV (ORCPT ); Tue, 30 Jul 2013 11:35:21 -0400 Received: from mail-ee0-f42.google.com ([74.125.83.42]:62771 "EHLO mail-ee0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751725Ab3G3PfT (ORCPT ); Tue, 30 Jul 2013 11:35:19 -0400 From: Artem Savkov To: peter@hurleysoftware.com Cc: gregkh@linuxfoundation.org, jslaby@suse.cz, linux-kernel@vger.kernel.org, Artem Savkov Subject: [PATCH] n_tty: release atomic_read_lock before calling schedule_timeout() Date: Tue, 30 Jul 2013 19:35:00 +0400 Message-Id: <1375198500-17414-1-git-send-email-artem.savkov@gmail.com> X-Mailer: git-send-email 1.7.0.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6031 Lines: 128 ldata->atomic_read_lock should be released before scheduling as well as tty->termios_rwsem, otherwise there is a potential deadlock detected by lockdep Introduced in "n_tty: Access termios values safely" (9356b535fcb71db494fc434acceb79f56d15bda2 in linux-next.git) [ 16.822058] ====================================================== [ 16.822058] [ INFO: possible circular locking dependency detected ] [ 16.822058] 3.11.0-rc3-next-20130730+ #140 Tainted: G W [ 16.822058] ------------------------------------------------------- [ 16.822058] bash/1198 is trying to acquire lock: [ 16.822058] (&tty->termios_rwsem){++++..}, at: [] n_tty_read+0x49b/0x660 [ 16.822058] [ 16.822058] but task is already holding lock: [ 16.822058] (&ldata->atomic_read_lock){+.+...}, at: [] n_tty_read+0x1d0/0x660 [ 16.822058] [ 16.822058] which lock already depends on the new lock. [ 16.822058] [ 16.822058] [ 16.822058] the existing dependency chain (in reverse order) is: [ 16.822058] -> #1 (&ldata->atomic_read_lock){+.+...}: [ 16.822058] [] validate_chain+0x73c/0x850 [ 16.822058] [] __lock_acquire+0x500/0x5d0 [ 16.822058] [] lock_acquire+0x179/0x1d0 [ 16.822058] [] mutex_lock_interruptible_nested+0x7c/0x540 [ 16.822058] [] n_tty_read+0x1d0/0x660 [ 16.822058] [] tty_read+0x86/0xf0 [ 16.822058] [] vfs_read+0xc3/0x130 [ 16.822058] [] SyS_read+0x62/0xa0 [ 16.822058] [] system_call_fastpath+0x16/0x1b [ 16.822058] -> #0 (&tty->termios_rwsem){++++..}: [ 16.822058] [] check_prev_add+0x14f/0x590 [ 16.822058] [] validate_chain+0x73c/0x850 [ 16.822058] [] __lock_acquire+0x500/0x5d0 [ 16.822058] [] lock_acquire+0x179/0x1d0 [ 16.822058] [] down_read+0x51/0xa0 [ 16.822058] [] n_tty_read+0x49b/0x660 [ 16.822058] [] tty_read+0x86/0xf0 [ 16.822058] [] vfs_read+0xc3/0x130 [ 16.822058] [] SyS_read+0x62/0xa0 [ 16.822058] [] system_call_fastpath+0x16/0x1b [ 16.822058] [ 16.822058] other info that might help us debug this: [ 16.822058] [ 16.822058] Possible unsafe locking scenario: [ 16.822058] [ 16.822058] CPU0 CPU1 [ 16.822058] ---- ---- [ 16.822058] lock(&ldata->atomic_read_lock); [ 16.822058] lock(&tty->termios_rwsem); [ 16.822058] lock(&ldata->atomic_read_lock); [ 16.822058] lock(&tty->termios_rwsem); [ 16.822058] [ 16.822058] *** DEADLOCK *** [ 16.822058] [ 16.822058] 2 locks held by bash/1198: [ 16.822058] #0: (&tty->ldisc_sem){.+.+.+}, at: [] tty_ldisc_ref_wait+0x24/0x60 [ 16.822058] #1: (&ldata->atomic_read_lock){+.+...}, at: [] n_tty_read+0x1d0/0x660 [ 16.822058] [ 16.822058] stack backtrace: [ 16.822058] CPU: 1 PID: 1198 Comm: bash Tainted: G W 3.11.0-rc3-next-20130730+ #140 [ 16.822058] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007 [ 16.822058] 0000000000000000 ffff880019acdb28 ffffffff81d34074 0000000000000002 [ 16.822058] 0000000000000000 ffff880019acdb78 ffffffff8110ed75 ffff880019acdb98 [ 16.822058] ffff880019fd0000 ffff880019acdb78 ffff880019fd0638 ffff880019fd0670 [ 16.822058] Call Trace: [ 16.822058] [] dump_stack+0x59/0x7d [ 16.822058] [] print_circular_bug+0x105/0x120 [ 16.822058] [] check_prev_add+0x14f/0x590 [ 16.822058] [] ? _raw_spin_unlock_irq+0x4f/0x70 [ 16.822058] [] validate_chain+0x73c/0x850 [ 16.822058] [] ? trace_hardirqs_off_caller+0x1f/0x190 [ 16.822058] [] __lock_acquire+0x500/0x5d0 [ 16.822058] [] lock_acquire+0x179/0x1d0 [ 16.822058] [] ? n_tty_read+0x49b/0x660 [ 16.822058] [] down_read+0x51/0xa0 [ 16.822058] [] ? n_tty_read+0x49b/0x660 [ 16.822058] [] n_tty_read+0x49b/0x660 [ 16.822058] [] ? try_to_wake_up+0x210/0x210 [ 16.822058] [] tty_read+0x86/0xf0 [ 16.822058] [] vfs_read+0xc3/0x130 [ 16.822058] [] SyS_read+0x62/0xa0 [ 16.822058] [] ? trace_hardirqs_on_thunk+0x3a/0x3f [ 16.822058] [] system_call_fastpath+0x16/0x1b Signed-off-by: Artem Savkov --- drivers/tty/n_tty.c | 12 ++++++++++++ 1 files changed, 12 insertions(+), 0 deletions(-) diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index dd8ae0c..38c09db 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -2203,11 +2203,23 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, break; } n_tty_set_room(tty); + mutex_unlock(&ldata->atomic_read_lock); up_read(&tty->termios_rwsem); timeout = schedule_timeout(timeout); down_read(&tty->termios_rwsem); + if (file->f_flags & O_NONBLOCK) { + if (!mutex_trylock(&ldata->atomic_read_lock)) { + retval = -EAGAIN; + break; + } + } else { + if (mutex_lock_interruptible(&ldata->atomic_read_lock)) { + retval = -ERESTARTSYS; + break; + } + } continue; } __set_current_state(TASK_RUNNING); -- 1.7.0.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/