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Date: Wed, 30 Dec 2015 11:44:01 +0100
From: Dmitry Vyukov <dvyukov@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jslaby@...e.com>,
LKML <linux-kernel@...r.kernel.org>,
J Freyensee <james_p_freyensee@...ux.intel.com>
Cc: syzkaller <syzkaller@...glegroups.com>,
Kostya Serebryany <kcc@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
Sasha Levin <sasha.levin@...cle.com>,
Eric Dumazet <edumazet@...gle.com>
Subject: tty: deadlock between n_tracerouter_receivebuf and flush_to_ldisc
Hello,
I've got the following lock order inversion report on
8513342170278468bac126640a5d2d12ffbff106 (Dec 28). Unfortunately I
failed to find a reproducer for it.
======================================================
[ INFO: possible circular locking dependency detected ]
4.4.0-rc7+ #181 Not tainted
-------------------------------------------------------
kworker/u9:2/35 is trying to acquire lock:
(routelock){+.+...}, at: [<ffffffff82bc77c0>]
n_tracerouter_receivebuf+0x20/0x40 drivers/tty/n_tracerouter.c:175
but task is already holding lock:
(&buf->lock){+.+...}, at: [<ffffffff82baf791>]
flush_to_ldisc+0xe1/0x7f0 drivers/tty/tty_buffer.c:487
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #3 (&buf->lock){+.+...}:
[<ffffffff813f0acf>] lock_acquire+0x19f/0x3c0
kernel/locking/lockdep.c:3585
[< inline >] __raw_spin_lock_irqsave
include/linux/spinlock_api_smp.h:112
[<ffffffff85c8e790>] _raw_spin_lock_irqsave+0x50/0x70
kernel/locking/spinlock.c:159
[<ffffffff82b8c050>] tty_get_pgrp+0x20/0x80 drivers/tty/tty_io.c:2502
[<ffffffff82b9a09a>] __isig+0x1a/0x50 drivers/tty/n_tty.c:1112
[<ffffffff82b9c16e>] isig+0xae/0x2c0 drivers/tty/n_tty.c:1131
[<ffffffff82b9ef02>] n_tty_receive_signal_char+0x22/0xf0
drivers/tty/n_tty.c:1243
[<ffffffff82ba4958>] n_tty_receive_char_special+0x1278/0x2bf0
drivers/tty/n_tty.c:1289
[< inline >] n_tty_receive_buf_fast drivers/tty/n_tty.c:1613
[< inline >] __receive_buf drivers/tty/n_tty.c:1647
[<ffffffff82ba7ca6>] n_tty_receive_buf_common+0x19d6/0x2450
drivers/tty/n_tty.c:1745
[<ffffffff82ba8753>] n_tty_receive_buf2+0x33/0x40
drivers/tty/n_tty.c:1780
[< inline >] receive_buf drivers/tty/tty_buffer.c:450
[<ffffffff82bafa6f>] flush_to_ldisc+0x3bf/0x7f0
drivers/tty/tty_buffer.c:517
[<ffffffff8133833c>] process_one_work+0x76c/0x13e0
kernel/workqueue.c:2030
[<ffffffff81339093>] worker_thread+0xe3/0xe90 kernel/workqueue.c:2162
[<ffffffff8134b63f>] kthread+0x23f/0x2d0 drivers/block/aoe/aoecmd.c:1303
[<ffffffff85c8eeef>] ret_from_fork+0x3f/0x70
arch/x86/entry/entry_64.S:468
-> #2 (&o_tty->termios_rwsem/1){++++..}:
[<ffffffff813f0acf>] lock_acquire+0x19f/0x3c0
kernel/locking/lockdep.c:3585
[<ffffffff85c899cc>] down_read+0x4c/0x70 kernel/locking/rwsem.c:22
[<ffffffff82ba635d>] n_tty_receive_buf_common+0x8d/0x2450
drivers/tty/n_tty.c:1708
[<ffffffff82ba8753>] n_tty_receive_buf2+0x33/0x40
drivers/tty/n_tty.c:1780
[< inline >] receive_buf drivers/tty/tty_buffer.c:450
[<ffffffff82bafa6f>] flush_to_ldisc+0x3bf/0x7f0
drivers/tty/tty_buffer.c:517
[<ffffffff8133833c>] process_one_work+0x76c/0x13e0
kernel/workqueue.c:2030
[<ffffffff81339093>] worker_thread+0xe3/0xe90 kernel/workqueue.c:2162
[<ffffffff8134b63f>] kthread+0x23f/0x2d0 drivers/block/aoe/aoecmd.c:1303
[<ffffffff85c8eeef>] ret_from_fork+0x3f/0x70
arch/x86/entry/entry_64.S:468
-> #1 (&port->buf.lock/1){+.+...}:
[<ffffffff813f0acf>] lock_acquire+0x19f/0x3c0
kernel/locking/lockdep.c:3585
[< inline >] __mutex_lock_common kernel/locking/mutex.c:518
[<ffffffff85c86ba6>] mutex_lock_nested+0xb6/0x940
kernel/locking/mutex.c:618
[<ffffffff82bc77ff>] n_tracerouter_open+0x1f/0x210
drivers/tty/n_tracerouter.c:75
[<ffffffff82bacd78>] tty_ldisc_open.isra.2+0x78/0xd0
drivers/tty/tty_ldisc.c:447
[<ffffffff82bad43a>] tty_set_ldisc+0x1ca/0xa30
drivers/tty/tty_ldisc.c:567
[< inline >] tiocsetd drivers/tty/tty_io.c:2650
[<ffffffff82b9483a>] tty_ioctl+0xb2a/0x2160 drivers/tty/tty_io.c:2883
[< inline >] vfs_ioctl fs/ioctl.c:43
[<ffffffff81750d41>] do_vfs_ioctl+0x681/0xe40 fs/ioctl.c:607
[< inline >] SYSC_ioctl fs/ioctl.c:622
[<ffffffff8175158f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:613
[<ffffffff85c8eb36>] entry_SYSCALL_64_fastpath+0x16/0x7a
arch/x86/entry/entry_64.S:185
-> #0 (routelock){+.+...}:
[< inline >] check_prev_add kernel/locking/lockdep.c:1853
[< inline >] check_prevs_add kernel/locking/lockdep.c:1958
[< inline >] validate_chain kernel/locking/lockdep.c:2144
[<ffffffff813ee02e>] __lock_acquire+0x345e/0x3ca0
kernel/locking/lockdep.c:3206
[<ffffffff813f0acf>] lock_acquire+0x19f/0x3c0
kernel/locking/lockdep.c:3585
[< inline >] __mutex_lock_common kernel/locking/mutex.c:518
[<ffffffff85c86ba6>] mutex_lock_nested+0xb6/0x940
kernel/locking/mutex.c:618
[<ffffffff82bc77c0>] n_tracerouter_receivebuf+0x20/0x40
drivers/tty/n_tracerouter.c:175
[< inline >] receive_buf drivers/tty/tty_buffer.c:454
[<ffffffff82bafc34>] flush_to_ldisc+0x584/0x7f0
drivers/tty/tty_buffer.c:517
[<ffffffff8133833c>] process_one_work+0x76c/0x13e0
kernel/workqueue.c:2030
[<ffffffff81339093>] worker_thread+0xe3/0xe90 kernel/workqueue.c:2162
[<ffffffff8134b63f>] kthread+0x23f/0x2d0 drivers/block/aoe/aoecmd.c:1303
[<ffffffff85c8eeef>] ret_from_fork+0x3f/0x70
arch/x86/entry/entry_64.S:468
other info that might help us debug this:
Chain exists of:
routelock --> &o_tty->termios_rwsem/1 --> &buf->lock
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&buf->lock);
lock(&o_tty->termios_rwsem/1);
lock(&buf->lock);
lock(routelock);
*** DEADLOCK ***
4 locks held by kworker/u9:2/35:
#0: ("events_unbound"){.+.+.+}, at: [< inline >]
__write_once_size include/linux/compiler.h:247
#0: ("events_unbound"){.+.+.+}, at: [< inline >]
atomic64_set ./arch/x86/include/asm/atomic64_64.h:33
#0: ("events_unbound"){.+.+.+}, at: [< inline >]
atomic_long_set include/asm-generic/atomic-long.h:56
#0: ("events_unbound"){.+.+.+}, at: [< inline >]
set_work_data kernel/workqueue.c:614
#0: ("events_unbound"){.+.+.+}, at: [< inline >]
set_work_pool_and_clear_pending kernel/workqueue.c:641
#0: ("events_unbound"){.+.+.+}, at: [<ffffffff81338242>]
process_one_work+0x672/0x13e0 kernel/workqueue.c:2023
#1: ((&buf->work)){+.+...}, at: [<ffffffff81338272>]
process_one_work+0x6a2/0x13e0 kernel/workqueue.c:2027
#2: (&tty->ldisc_sem){++++++}, at: [<ffffffff82bac99b>]
tty_ldisc_ref+0x1b/0x80 drivers/tty/tty_ldisc.c:283
#3: (&buf->lock){+.+...}, at: [<ffffffff82baf791>]
flush_to_ldisc+0xe1/0x7f0 drivers/tty/tty_buffer.c:487
stack backtrace:
CPU: 0 PID: 35 Comm: kworker/u9:2 Not tainted 4.4.0-rc7+ #181
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Workqueue: events_unbound flush_to_ldisc
00000000ffffffff ffff88003d8e77f8 ffffffff8289d9dd ffffffff8866fbf0
ffffffff8863f050 ffffffff886422f0 ffff88003d8e7840 ffffffff813e7081
ffff88003d8e7930 000000003d8b1780 ffff88003d8b1fc0 ffff88003d8b1fe2
Call Trace:
[< inline >] validate_chain kernel/locking/lockdep.c:2144
[<ffffffff813ee02e>] __lock_acquire+0x345e/0x3ca0 kernel/locking/lockdep.c:3206
[<ffffffff813f0acf>] lock_acquire+0x19f/0x3c0 kernel/locking/lockdep.c:3585
[< inline >] __mutex_lock_common kernel/locking/mutex.c:518
[<ffffffff85c86ba6>] mutex_lock_nested+0xb6/0x940 kernel/locking/mutex.c:618
[<ffffffff82bc77c0>] n_tracerouter_receivebuf+0x20/0x40
drivers/tty/n_tracerouter.c:175
[< inline >] receive_buf drivers/tty/tty_buffer.c:454
[<ffffffff82bafc34>] flush_to_ldisc+0x584/0x7f0 drivers/tty/tty_buffer.c:517
[<ffffffff8133833c>] process_one_work+0x76c/0x13e0 kernel/workqueue.c:2030
[<ffffffff81339093>] worker_thread+0xe3/0xe90 kernel/workqueue.c:2162
[<ffffffff8134b63f>] kthread+0x23f/0x2d0 drivers/block/aoe/aoecmd.c:1303
[<ffffffff85c8eeef>] ret_from_fork+0x3f/0x70 arch/x86/entry/entry_64.S:468
======================================================
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