Messages in this thread | | | Date | Tue, 2 Oct 2012 18:14:08 +0200 (CEST) | From | Jiri Kosina <> | Subject | Lockdep complains about commit 1331e7a1bb ("rcu: Remove _rcu_barrier() dependency on __stop_machine()") |
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Hi,
this commit:
== 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.
====================================================== [ 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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