Messages in this thread | | | Date | Tue, 2 Oct 2012 23:27:04 +0200 (CEST) | From | Jiri Kosina <> | Subject | Re: Lockdep complains about commit 1331e7a1bb ("rcu: Remove _rcu_barrier() dependency on __stop_machine()") |
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On Tue, 2 Oct 2012, Paul E. McKenney wrote:
> > 1331e7a1bbe1f11b19c4327ba0853bee2a606543 is the first bad commit > > commit 1331e7a1bbe1f11b19c4327ba0853bee2a606543 > > Author: Paul E. McKenney <paul.mckenney@linaro.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@linaro.org> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > Reviewed-by: Josh Triplett <josh@joshtriplett.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. > > Hmmm... Does the following patch help? It swaps the order in which > rcu_barrier() acquires the hotplug and rcu_barrier locks.
It changed the report slightly (see for example the change in possible unsafe locking scenario, rcu_sched_state.barrier_mutex vanished and it's now directly about cpu_hotplug.lock). With the patch applied I get
====================================================== [ INFO: possible circular locking dependency detected ] 3.6.0-03888-g3f99f3b #145 Not tainted ------------------------------------------------------- kworker/u:3/43 is trying to acquire lock: (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff81049287>] get_online_cpus+0x37/0x50
but task is already holding lock: (slab_mutex){+.+.+.}, at: [<ffffffff81178175>] kmem_cache_destroy+0x45/0xe0
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (slab_mutex){+.+.+.}: [<ffffffff810aeb22>] validate_chain+0x632/0x720 [<ffffffff810aef69>] __lock_acquire+0x359/0x580 [<ffffffff810af2b1>] lock_acquire+0x121/0x190 [<ffffffff8156130c>] __mutex_lock_common+0x5c/0x450 [<ffffffff8156182e>] mutex_lock_nested+0x3e/0x50 [<ffffffff8155cafa>] cpuup_callback+0x2f/0xbe [<ffffffff81568bc3>] notifier_call_chain+0x93/0x140 [<ffffffff81077289>] __raw_notifier_call_chain+0x9/0x10 [<ffffffff8155b1ac>] _cpu_up+0xc9/0x162 [<ffffffff8155b301>] cpu_up+0xbc/0x11b [<ffffffff81ae1793>] smp_init+0x6b/0x9f [<ffffffff81ac57d6>] kernel_init+0x147/0x1dc [<ffffffff8156eca4>] kernel_thread_helper+0x4/0x10
-> #0 (cpu_hotplug.lock){+.+.+.}: [<ffffffff810ae48e>] check_prev_add+0x3de/0x440 [<ffffffff810aeb22>] validate_chain+0x632/0x720 [<ffffffff810aef69>] __lock_acquire+0x359/0x580 [<ffffffff810af2b1>] lock_acquire+0x121/0x190 [<ffffffff8156130c>] __mutex_lock_common+0x5c/0x450 [<ffffffff8156182e>] mutex_lock_nested+0x3e/0x50 [<ffffffff81049287>] get_online_cpus+0x37/0x50 [<ffffffff810f3a92>] _rcu_barrier+0x22/0x1f0 [<ffffffff810f3c70>] rcu_barrier_sched+0x10/0x20 [<ffffffff810f3c89>] rcu_barrier+0x9/0x10 [<ffffffff81178201>] kmem_cache_destroy+0xd1/0xe0 [<ffffffffa0488154>] nf_conntrack_cleanup_net+0xe4/0x110 [nf_conntrack] [<ffffffffa04881aa>] nf_conntrack_cleanup+0x2a/0x70 [nf_conntrack] [<ffffffffa04892ce>] nf_conntrack_net_exit+0x5e/0x80 [nf_conntrack] [<ffffffff81458629>] ops_exit_list+0x39/0x60 [<ffffffff81458c5b>] cleanup_net+0xfb/0x1b0 [<ffffffff810691eb>] process_one_work+0x26b/0x4c0 [<ffffffff8106a03e>] worker_thread+0x12e/0x320 [<ffffffff8106f86e>] kthread+0xde/0xf0 [<ffffffff8156eca4>] kernel_thread_helper+0x4/0x10
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(slab_mutex); lock(cpu_hotplug.lock); lock(slab_mutex); lock(cpu_hotplug.lock);
*** DEADLOCK ***
4 locks held by kworker/u:3/43: #0: (netns){.+.+.+}, at: [<ffffffff81069122>] process_one_work+0x1a2/0x4c0 #1: (net_cleanup_work){+.+.+.}, at: [<ffffffff81069122>] process_one_work+0x1a2/0x4c0 #2: (net_mutex){+.+.+.}, at: [<ffffffff81458be0>] cleanup_net+0x80/0x1b0 #3: (slab_mutex){+.+.+.}, at: [<ffffffff81178175>] kmem_cache_destroy+0x45/0xe0
stack backtrace: Pid: 43, comm: kworker/u:3 Not tainted 3.6.0-03888-g3f99f3b #145 Call Trace: [<ffffffff810ac5cf>] print_circular_bug+0x10f/0x120 [<ffffffff810ae48e>] check_prev_add+0x3de/0x440 [<ffffffff810aeb22>] validate_chain+0x632/0x720 [<ffffffff810aef69>] __lock_acquire+0x359/0x580 [<ffffffff810af2b1>] lock_acquire+0x121/0x190 [<ffffffff81049287>] ? get_online_cpus+0x37/0x50 [<ffffffff8156130c>] __mutex_lock_common+0x5c/0x450 [<ffffffff81049287>] ? get_online_cpus+0x37/0x50 [<ffffffff810ada40>] ? mark_held_locks+0x80/0x120 [<ffffffff81049287>] ? get_online_cpus+0x37/0x50 [<ffffffff8156182e>] mutex_lock_nested+0x3e/0x50 [<ffffffff81049287>] get_online_cpus+0x37/0x50 [<ffffffff810f3a92>] _rcu_barrier+0x22/0x1f0 [<ffffffff810f3c70>] rcu_barrier_sched+0x10/0x20 [<ffffffff810f3c89>] rcu_barrier+0x9/0x10 [<ffffffff81178201>] kmem_cache_destroy+0xd1/0xe0 [<ffffffffa0488154>] nf_conntrack_cleanup_net+0xe4/0x110 [nf_conntrack] [<ffffffffa04881aa>] nf_conntrack_cleanup+0x2a/0x70 [nf_conntrack] [<ffffffffa04892ce>] nf_conntrack_net_exit+0x5e/0x80 [nf_conntrack] [<ffffffff81458629>] ops_exit_list+0x39/0x60 [<ffffffff81458c5b>] cleanup_net+0xfb/0x1b0 [<ffffffff810691eb>] process_one_work+0x26b/0x4c0 [<ffffffff81069122>] ? process_one_work+0x1a2/0x4c0 [<ffffffff81069f69>] ? worker_thread+0x59/0x320 [<ffffffff81458b60>] ? net_drop_ns+0x40/0x40 [<ffffffff8106a03e>] worker_thread+0x12e/0x320 [<ffffffff81069f10>] ? manage_workers+0x1a0/0x1a0 [<ffffffff8106f86e>] kthread+0xde/0xf0 [<ffffffff8156eca4>] kernel_thread_helper+0x4/0x10 [<ffffffff81564b33>] ? retint_restore_args+0x13/0x13 [<ffffffff8106f790>] ? __init_kthread_worker+0x70/0x70 [<ffffffff8156eca0>] ? gs_change+0x13/0x13
-- Jiri Kosina SUSE Labs
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