Re: perf related lockdep bug

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Nov 04, 2015 at 12:17:17AM -0500, Dave Jones wrote:
> This is new to me since todays merge window.
> 

Thanks, 'interesting' indeed. I've one complaint from Andi about his
machine going belly up which might maybe be explained by this.

The problem appears to be due to the new RCU expedited grace period
stuff, with rcu_read_unlock() now randomly trying to acquire locks it
previously didn't.

Lemme go look at those rcu bits again..

---

> [  293.955261] ======================================================
> [  293.955395] [ INFO: possible circular locking dependency detected ]
> [  293.955536] 4.3.0-think+ #3 Not tainted
> [  293.955618] -------------------------------------------------------
> [  293.955756] trinity-c343/12586 is trying to acquire lock:
> [  293.955875]  (rcu_node_0){-.-...}, at: [<ffffffffb00eb734>] rcu_report_exp_cpu_mult+0x24/0x70
> [  293.956070] 
>                but task is already holding lock:
> [  293.956194]  (&ctx->lock){-.....}, at: [<ffffffffb0180453>] perf_lock_task_context+0x53/0x300
> [  293.956386] 
>                which lock already depends on the new lock.
> 
> [  293.956559] 
>                the existing dependency chain (in reverse order) is:
> [  293.956720] 
>                -> #3 (&ctx->lock){-.....}:
> [  293.956807]        [<ffffffffb00d53a3>] lock_acquire+0xc3/0x1d0
> [  293.956940]        [<ffffffffb07efdd1>] _raw_spin_lock+0x41/0x80
> [  293.957075]        [<ffffffffb0185b66>] __perf_event_task_sched_out+0x276/0x700
> [  293.957239]        [<ffffffffb07e9f70>] __schedule+0x530/0xaf0
> [  293.957370]        [<ffffffffb07ea6df>] schedule+0x3f/0x90
> [  293.957493]        [<ffffffffb0001206>] exit_to_usermode_loop+0x76/0xa0
> [  293.957642]        [<ffffffffb0001c13>] prepare_exit_to_usermode+0x53/0x60
> [  293.957795]        [<ffffffffb07f1867>] retint_user+0x8/0x20
> [  293.957923] 
>                -> #2 (&rq->lock){-.-.-.}:
> [  293.958008]        [<ffffffffb00d53a3>] lock_acquire+0xc3/0x1d0
> [  293.958140]        [<ffffffffb07efdd1>] _raw_spin_lock+0x41/0x80
> [  293.958275]        [<ffffffffb00b198d>] sched_move_task+0x4d/0x270
> [  293.958417]        [<ffffffffb00b1bde>] cpu_cgroup_fork+0xe/0x10
> [  293.958551]        [<ffffffffb012a057>] cgroup_post_fork+0x67/0x160
> [  293.958692]        [<ffffffffb007ae0a>] copy_process+0x147a/0x1e10
> [  293.958831]        [<ffffffffb007b927>] _do_fork+0x97/0x680
> [  293.958955]        [<ffffffffb007bf39>] kernel_thread+0x29/0x30
> [  293.959087]        [<ffffffffb07e8477>] rest_init+0x27/0x140
> [  293.959211]        [<ffffffffb0ef1f72>] start_kernel+0x450/0x45d
> [  293.959347]        [<ffffffffb0ef12fe>] x86_64_start_reservations+0x2a/0x2c
> [  293.959503]        [<ffffffffb0ef1468>] x86_64_start_kernel+0x168/0x176
> [  293.959652] 
>                -> #1 (&p->pi_lock){-.-.-.}:
> [  293.959742]        [<ffffffffb00d53a3>] lock_acquire+0xc3/0x1d0
> [  293.959876]        [<ffffffffb07f00ec>] _raw_spin_lock_irqsave+0x4c/0x90
> [  293.960026]        [<ffffffffb00ac070>] try_to_wake_up+0x30/0x5f0
> [  293.960165]        [<ffffffffb00ac653>] wake_up_process+0x23/0x40
> [  293.960300]        [<ffffffffb0f0b7a0>] rcu_spawn_gp_kthread+0xd5/0xfd
> [  293.960449]        [<ffffffffb00002d3>] do_one_initcall+0xb3/0x1f0
> [  293.960587]        [<ffffffffb0ef2080>] kernel_init_freeable+0x101/0x234
> [  293.960736]        [<ffffffffb07e859e>] kernel_init+0xe/0xe0
> [  293.960860]        [<ffffffffb07f10ff>] ret_from_fork+0x3f/0x70
> [  293.960993] 
>                -> #0 (rcu_node_0){-.-...}:
> [  293.961081]        [<ffffffffb00d4722>] __lock_acquire+0x19d2/0x1cf0
> [  293.961222]        [<ffffffffb00d53a3>] lock_acquire+0xc3/0x1d0
> [  293.961351]        [<ffffffffb07f00ec>] _raw_spin_lock_irqsave+0x4c/0x90
> [  293.961501]        [<ffffffffb00eb734>] rcu_report_exp_cpu_mult+0x24/0x70
> [  293.961652]        [<ffffffffb00f48e9>] rcu_read_unlock_special+0x109/0x5e0
> [  293.961808]        [<ffffffffb00e88f7>] __rcu_read_unlock+0x87/0x90
> [  293.961947]        [<ffffffffb018059d>] perf_lock_task_context+0x19d/0x300
> [  293.962101]        [<ffffffffb018b5bf>] perf_event_init_task+0x9f/0x370
> [  293.962248]        [<ffffffffb007a18a>] copy_process+0x7fa/0x1e10
> [  293.962385]        [<ffffffffb007b927>] _do_fork+0x97/0x680
> [  293.962508]        [<ffffffffb007bfb9>] SyS_clone+0x19/0x20
> [  293.962631]        [<ffffffffb07f0d97>] entry_SYSCALL_64_fastpath+0x12/0x6f
> [  293.962787] 
>                other info that might help us debug this:
> 
> [  293.962955] Chain exists of:
>                  rcu_node_0 --> &rq->lock --> &ctx->lock
> 
> [  293.963106]  Possible unsafe locking scenario:
> 
> [  293.963233]        CPU0                    CPU1
> [  293.963332]        ----                    ----
> [  293.963430]   lock(&ctx->lock);
> [  293.963500]                                lock(&rq->lock);
> [  293.963627]                                lock(&ctx->lock);
> [  293.963755]   lock(rcu_node_0);
> [  293.963824] 
>                 *** DEADLOCK ***
> 
> [  293.963947] 2 locks held by trinity-c343/12586:
> [  293.964047]  #0:  (rcu_read_lock){......}, at: [<ffffffffb01804d0>] perf_lock_task_context+0xd0/0x300
> [  293.964258]  #1:  (&ctx->lock){-.....}, at: [<ffffffffb0180453>] perf_lock_task_context+0x53/0x300
> [  293.972934] 
>                stack backtrace:
> [  293.990221] CPU: 3 PID: 12586 Comm: trinity-c343 Not tainted 4.3.0-think+ #3
> [  293.999210]  ffff8804fb6824a0 ffff88044a0efa60 ffffffffb03607bc ffffffffb1779630
> [  294.008115]  ffff88044a0efaa0 ffffffffb00d1453 ffff88044a0efb10 0000000000000002
> [  294.017066]  ffff8804fb682468 ffff8804fb6824a0 0000000000000001 ffff8804fb681b80
> [  294.026109] Call Trace:
> [  294.035079]  [<ffffffffb03607bc>] dump_stack+0x4e/0x82
> [  294.044014]  [<ffffffffb00d1453>] print_circular_bug+0x1e3/0x250
> [  294.052982]  [<ffffffffb00d4722>] __lock_acquire+0x19d2/0x1cf0
> [  294.061926]  [<ffffffffb00cedf9>] ? get_lock_stats+0x19/0x60
> [  294.070878]  [<ffffffffb00d53a3>] lock_acquire+0xc3/0x1d0
> [  294.079828]  [<ffffffffb00eb734>] ? rcu_report_exp_cpu_mult+0x24/0x70
> [  294.088805]  [<ffffffffb07f00ec>] _raw_spin_lock_irqsave+0x4c/0x90
> [  294.097771]  [<ffffffffb00eb734>] ? rcu_report_exp_cpu_mult+0x24/0x70
> [  294.106807]  [<ffffffffb00eb734>] rcu_report_exp_cpu_mult+0x24/0x70
> [  294.115823]  [<ffffffffb00f48e9>] rcu_read_unlock_special+0x109/0x5e0
> [  294.124813]  [<ffffffffb00cedf9>] ? get_lock_stats+0x19/0x60
> [  294.133801]  [<ffffffffb0180453>] ? perf_lock_task_context+0x53/0x300
> [  294.142790]  [<ffffffffb00e88f7>] __rcu_read_unlock+0x87/0x90
> [  294.151675]  [<ffffffffb018059d>] perf_lock_task_context+0x19d/0x300
> [  294.160420]  [<ffffffffb01804d0>] ? perf_lock_task_context+0xd0/0x300
> [  294.169166]  [<ffffffffb018b5bf>] perf_event_init_task+0x9f/0x370
> [  294.177832]  [<ffffffffb00a64a5>] ? preempt_count_sub+0xa5/0xf0
> [  294.186477]  [<ffffffffb007a18a>] copy_process+0x7fa/0x1e10
> [  294.195036]  [<ffffffffb00cedf9>] ? get_lock_stats+0x19/0x60
> [  294.203564]  [<ffffffffb00ced1d>] ? trace_hardirqs_off+0xd/0x10
> [  294.212042]  [<ffffffffb0146101>] ? __acct_update_integrals+0x91/0xf0
> [  294.220411]  [<ffffffffb00a64a5>] ? preempt_count_sub+0xa5/0xf0
> [  294.228778]  [<ffffffffb007b927>] _do_fork+0x97/0x680
> [  294.237038]  [<ffffffffb018fd73>] ? context_tracking_user_exit+0x13/0x20
> [  294.245322]  [<ffffffffb00017ca>] ? enter_from_user_mode+0x1a/0x50
> [  294.253586]  [<ffffffffb00018bc>] ? syscall_trace_enter_phase1+0xbc/0x110
> [  294.261919]  [<ffffffffb0001017>] ? trace_hardirqs_on_thunk+0x17/0x19
> [  294.270306]  [<ffffffffb007bfb9>] SyS_clone+0x19/0x20
> [  294.278672]  [<ffffffffb07f0d97>] entry_SYSCALL_64_fastpath+0x12/0x6f
>