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Date: Tue, 2 Oct 2012 18:14:08 +0200 (CEST)
From: Jiri Kosina <jkosina@...e.cz>
To: "Paul E. McKenney" <paul.mckenney@...aro.org>,
Josh Triplett <josh@...htriplett.org>
Cc: linux-kernel@...r.kernel.org
Subject: Lockdep complains about commit 1331e7a1bb ("rcu: Remove _rcu_barrier()
dependency on __stop_machine()")
Hi,
this commit:
==
1331e7a1bbe1f11b19c4327ba0853bee2a606543 is the first bad commit
commit 1331e7a1bbe1f11b19c4327ba0853bee2a606543
Author: Paul E. McKenney <paul.mckenney@...aro.org>
Date: Thu Aug 2 17:43:50 2012 -0700
rcu: Remove _rcu_barrier() dependency on __stop_machine()
Currently, _rcu_barrier() relies on preempt_disable() to prevent
any CPU from going offline, which in turn depends on CPU hotplug's
use of __stop_machine().
This patch therefore makes _rcu_barrier() use get_online_cpus() to
block CPU-hotplug operations. This has the added benefit of removing
the need for _rcu_barrier() to adopt callbacks: Because CPU-hotplug
operations are excluded, there can be no callbacks to adopt. This
commit simplifies the code accordingly.
Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@...htriplett.org>
==
is causing lockdep to complain (see the full trace below). I haven't yet
had time to analyze what exactly is happening, and probably will not have
time to do so until tomorrow, so just sending this as a heads-up in case
anyone sees the culprit immediately.
======================================================
[ INFO: possible circular locking dependency detected ]
3.6.0-rc5-00004-g0d8ee37 #143 Not tainted
-------------------------------------------------------
kworker/u:2/40 is trying to acquire lock:
(rcu_sched_state.barrier_mutex){+.+...}, at: [<ffffffff810f2126>] _rcu_barrier+0x26/0x1e0
but task is already holding lock:
(slab_mutex){+.+.+.}, at: [<ffffffff81176e15>] kmem_cache_destroy+0x45/0xe0
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (slab_mutex){+.+.+.}:
[<ffffffff810ae1e2>] validate_chain+0x632/0x720
[<ffffffff810ae5d9>] __lock_acquire+0x309/0x530
[<ffffffff810ae921>] lock_acquire+0x121/0x190
[<ffffffff8155d4cc>] __mutex_lock_common+0x5c/0x450
[<ffffffff8155d9ee>] mutex_lock_nested+0x3e/0x50
[<ffffffff81558cb5>] cpuup_callback+0x2f/0xbe
[<ffffffff81564b83>] notifier_call_chain+0x93/0x140
[<ffffffff81076f89>] __raw_notifier_call_chain+0x9/0x10
[<ffffffff8155719d>] _cpu_up+0xba/0x14e
[<ffffffff815572ed>] cpu_up+0xbc/0x117
[<ffffffff81ae05e3>] smp_init+0x6b/0x9f
[<ffffffff81ac47d6>] kernel_init+0x147/0x1dc
[<ffffffff8156ab44>] kernel_thread_helper+0x4/0x10
-> #1 (cpu_hotplug.lock){+.+.+.}:
[<ffffffff810ae1e2>] validate_chain+0x632/0x720
[<ffffffff810ae5d9>] __lock_acquire+0x309/0x530
[<ffffffff810ae921>] lock_acquire+0x121/0x190
[<ffffffff8155d4cc>] __mutex_lock_common+0x5c/0x450
[<ffffffff8155d9ee>] mutex_lock_nested+0x3e/0x50
[<ffffffff81049197>] get_online_cpus+0x37/0x50
[<ffffffff810f21bb>] _rcu_barrier+0xbb/0x1e0
[<ffffffff810f22f0>] rcu_barrier_sched+0x10/0x20
[<ffffffff810f2309>] rcu_barrier+0x9/0x10
[<ffffffff8118c129>] deactivate_locked_super+0x49/0x90
[<ffffffff8118cc01>] deactivate_super+0x61/0x70
[<ffffffff811aaaa7>] mntput_no_expire+0x127/0x180
[<ffffffff811ab49e>] sys_umount+0x6e/0xd0
[<ffffffff81569979>] system_call_fastpath+0x16/0x1b
-> #0 (rcu_sched_state.barrier_mutex){+.+...}:
[<ffffffff810adb4e>] check_prev_add+0x3de/0x440
[<ffffffff810ae1e2>] validate_chain+0x632/0x720
[<ffffffff810ae5d9>] __lock_acquire+0x309/0x530
[<ffffffff810ae921>] lock_acquire+0x121/0x190
[<ffffffff8155d4cc>] __mutex_lock_common+0x5c/0x450
[<ffffffff8155d9ee>] mutex_lock_nested+0x3e/0x50
[<ffffffff810f2126>] _rcu_barrier+0x26/0x1e0
[<ffffffff810f22f0>] rcu_barrier_sched+0x10/0x20
[<ffffffff810f2309>] rcu_barrier+0x9/0x10
[<ffffffff81176ea1>] kmem_cache_destroy+0xd1/0xe0
[<ffffffffa04c3154>] nf_conntrack_cleanup_net+0xe4/0x110 [nf_conntrack]
[<ffffffffa04c31aa>] nf_conntrack_cleanup+0x2a/0x70 [nf_conntrack]
[<ffffffffa04c42ce>] nf_conntrack_net_exit+0x5e/0x80 [nf_conntrack]
[<ffffffff81454b79>] ops_exit_list+0x39/0x60
[<ffffffff814551ab>] cleanup_net+0xfb/0x1b0
[<ffffffff8106917b>] process_one_work+0x26b/0x4c0
[<ffffffff81069f3e>] worker_thread+0x12e/0x320
[<ffffffff8106f73e>] kthread+0x9e/0xb0
[<ffffffff8156ab44>] kernel_thread_helper+0x4/0x10
other info that might help us debug this:
Chain exists of:
rcu_sched_state.barrier_mutex --> cpu_hotplug.lock --> slab_mutex
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(slab_mutex);
lock(cpu_hotplug.lock);
lock(slab_mutex);
lock(rcu_sched_state.barrier_mutex);
*** DEADLOCK ***
4 locks held by kworker/u:2/40:
#0: (netns){.+.+.+}, at: [<ffffffff810690b2>] process_one_work+0x1a2/0x4c0
#1: (net_cleanup_work){+.+.+.}, at: [<ffffffff810690b2>] process_one_work+0x1a2/0x4c0
#2: (net_mutex){+.+.+.}, at: [<ffffffff81455130>] cleanup_net+0x80/0x1b0
#3: (slab_mutex){+.+.+.}, at: [<ffffffff81176e15>] kmem_cache_destroy+0x45/0xe0
stack backtrace:
Pid: 40, comm: kworker/u:2 Not tainted 3.6.0-rc5-00004-g0d8ee37 #143
Call Trace:
[<ffffffff810ac85f>] print_circular_bug+0x10f/0x120
[<ffffffff810adb4e>] check_prev_add+0x3de/0x440
[<ffffffff810ad85a>] ? check_prev_add+0xea/0x440
[<ffffffff8102c72f>] ? flat_send_IPI_mask+0x7f/0xc0
[<ffffffff810ae1e2>] validate_chain+0x632/0x720
[<ffffffff810ae5d9>] __lock_acquire+0x309/0x530
[<ffffffff810ae921>] lock_acquire+0x121/0x190
[<ffffffff810f2126>] ? _rcu_barrier+0x26/0x1e0
[<ffffffff8155d4cc>] __mutex_lock_common+0x5c/0x450
[<ffffffff810f2126>] ? _rcu_barrier+0x26/0x1e0
[<ffffffff810b5e45>] ? on_each_cpu+0x65/0xc0
[<ffffffff810f2126>] ? _rcu_barrier+0x26/0x1e0
[<ffffffff8155d9ee>] mutex_lock_nested+0x3e/0x50
[<ffffffff810f2126>] _rcu_barrier+0x26/0x1e0
[<ffffffff810f22f0>] rcu_barrier_sched+0x10/0x20
[<ffffffff810f2309>] rcu_barrier+0x9/0x10
[<ffffffff81176ea1>] kmem_cache_destroy+0xd1/0xe0
[<ffffffffa04c3154>] nf_conntrack_cleanup_net+0xe4/0x110 [nf_conntrack]
[<ffffffffa04c31aa>] nf_conntrack_cleanup+0x2a/0x70 [nf_conntrack]
[<ffffffffa04c42ce>] nf_conntrack_net_exit+0x5e/0x80 [nf_conntrack]
[<ffffffff81454b79>] ops_exit_list+0x39/0x60
[<ffffffff814551ab>] cleanup_net+0xfb/0x1b0
[<ffffffff8106917b>] process_one_work+0x26b/0x4c0
[<ffffffff810690b2>] ? process_one_work+0x1a2/0x4c0
[<ffffffff81069e69>] ? worker_thread+0x59/0x320
[<ffffffff814550b0>] ? net_drop_ns+0x40/0x40
[<ffffffff81069f3e>] worker_thread+0x12e/0x320
[<ffffffff81069e10>] ? manage_workers+0x110/0x110
[<ffffffff8106f73e>] kthread+0x9e/0xb0
[<ffffffff8156ab44>] kernel_thread_helper+0x4/0x10
[<ffffffff81560b70>] ? retint_restore_args+0x13/0x13
[<ffffffff8106f6a0>] ? __init_kthread_worker+0x70/0x70
[<ffffffff8156ab40>] ? gs_change+0x13/0x13
--
Jiri Kosina
SUSE Labs
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