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Date: Sat, 20 Dec 2014 00:25:57 +0530
From: Arun KS <arunks.linux@...il.com>
To: Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
josh@...htriplett.org, rostedt@...dmis.org,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
laijs@...fujitsu.com, Arun KS <getarunks@...il.com>
Subject: Re: [RCU] kernel hangs in wait_rcu_gp during suspend path
Hi Paul,
On Fri, Dec 19, 2014 at 1:35 AM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Thu, Dec 18, 2014 at 09:52:28PM +0530, Arun KS wrote:
>> Hi Paul,
>>
>> On Thu, Dec 18, 2014 at 12:54 AM, Paul E. McKenney
>> <paulmck@...ux.vnet.ibm.com> wrote:
>> > On Tue, Dec 16, 2014 at 11:00:20PM +0530, Arun KS wrote:
>> >> Hello,
>> >>
>> >> Adding some more info.
>> >>
>> >> Below is the rcu_data data structure corresponding to cpu4.
>> >
>> > This shows that RCU is idle. What was the state of the system at the
>> > time you collected this data?
>>
>> System initiated a suspend sequence and currently at disable_nonboot_cpus().
>> It has hotplugged 0, 1 and 2 successfully. And even successful in hot
>> plugging cpu3.
>> But while calling the CPU_POST_DEAD notifier for cpu3, another driver tried to
>> unregister an atomic notifier. Which eventually calls syncronize_rcu()
>> which hangs the suspend task.
>>
>> bt as follows,
>> PID: 202 TASK: edcd2a00 CPU: 4 COMMAND: "kworker/u16:4"
>> #0 [<c0a1f8c0>] (__schedule) from [<c0a1d054>]
>> #1 [<c0a1d054>] (schedule_timeout) from [<c0a1f018>]
>> #2 [<c0a1f018>] (wait_for_common) from [<c013c570>]
>> #3 [<c013c570>] (wait_rcu_gp) from [<c014407c>]
>> #4 [<c014407c>] (atomic_notifier_chain_unregister) from [<c06be62c>]
>> #5 [<c06be62c>] (cpufreq_interactive_disable_sched_input) from [<c06bee1c>]
>> #6 [<c06bee1c>] (cpufreq_governor_interactive) from [<c06b7724>]
>> #7 [<c06b7724>] (__cpufreq_governor) from [<c06b9f74>]
>> #8 [<c06b9f74>] (__cpufreq_remove_dev_finish) from [<c06ba3a4>]
>> #9 [<c06ba3a4>] (cpufreq_cpu_callback) from [<c0a22674>]
>> #10 [<c0a22674>] (notifier_call_chain) from [<c012284c>]
>> #11 [<c012284c>] (__cpu_notify) from [<c01229dc>]
>> #12 [<c01229dc>] (cpu_notify_nofail) from [<c0a0dd1c>]
>> #13 [<c0a0dd1c>] (_cpu_down) from [<c0122b48>]
>> #14 [<c0122b48>] (disable_nonboot_cpus) from [<c0168cd8>]
>> #15 [<c0168cd8>] (suspend_devices_and_enter) from [<c0169018>]
>> #16 [<c0169018>] (pm_suspend) from [<c01691e0>]
>> #17 [<c01691e0>] (try_to_suspend) from [<c01396f0>]
>> #18 [<c01396f0>] (process_one_work) from [<c0139db0>]
>> #19 [<c0139db0>] (worker_thread) from [<c013efa4>]
>> #20 [<c013efa4>] (kthread) from [<c01061f8>]
>>
>> But the other cores 4-7 are active. I can see them going to idle tasks
>> coming out from idle because of interrupts, scheduling kworkers etc.
>> So when I took the data, all the online cores(4-7) were in idle as
>> shown below from runq data structures.
>>
>> ------start--------------
>> crash> runq
>> CPU 0 [OFFLINE]
>>
>> CPU 1 [OFFLINE]
>>
>> CPU 2 [OFFLINE]
>>
>> CPU 3 [OFFLINE]
>>
>> CPU 4 RUNQUEUE: c5439040
>> CURRENT: PID: 0 TASK: f0c9d400 COMMAND: "swapper/4"
>> RT PRIO_ARRAY: c5439130
>> [no tasks queued]
>> CFS RB_ROOT: c54390c0
>> [no tasks queued]
>>
>> CPU 5 RUNQUEUE: c5447040
>> CURRENT: PID: 0 TASK: f0c9aa00 COMMAND: "swapper/5"
>> RT PRIO_ARRAY: c5447130
>> [no tasks queued]
>> CFS RB_ROOT: c54470c0
>> [no tasks queued]
>>
>> CPU 6 RUNQUEUE: c5455040
>> CURRENT: PID: 0 TASK: f0c9ce00 COMMAND: "swapper/6"
>> RT PRIO_ARRAY: c5455130
>> [no tasks queued]
>> CFS RB_ROOT: c54550c0
>> [no tasks queued]
>>
>> CPU 7 RUNQUEUE: c5463040
>> CURRENT: PID: 0 TASK: f0c9b000 COMMAND: "swapper/7"
>> RT PRIO_ARRAY: c5463130
>> [no tasks queued]
>> CFS RB_ROOT: c54630c0
>> [no tasks queued]
>> ------end--------------
>>
>> but one strange thing i can see is that rcu_read_lock_nesting for idle
>> tasks running on cpu 5 and cpu 6 are set to 1.
>>
>> PID: 0 TASK: f0c9d400 CPU: 4 COMMAND: "swapper/4"
>> rcu_read_lock_nesting = 0,
>>
>> PID: 0 TASK: f0c9aa00 CPU: 5 COMMAND: "swapper/5"
>> rcu_read_lock_nesting = 1,
>>
>> PID: 0 TASK: f0c9ce00 CPU: 6 COMMAND: "swapper/6"
>> rcu_read_lock_nesting = 1,
>>
>> PID: 0 TASK: f0c9b000 CPU: 7 COMMAND: "swapper/7"
>> rcu_read_lock_nesting = 0,
>>
>> Does this means that the current grace period(suspend thread is
>> waiting on) is getting extended infinitely?
>
> Indeed it does, good catch! Looks like someone entered an RCU read-side
> critical section, then forgot to exit it, which would prevent grace
> periods from ever completing. CONFIG_PROVE_RCU=y might be
> helpful in tracking this down.
>
>> Also attaching the per_cpu rcu_data for online and offline cores.
>
> But these still look like there is no grace period in progress.
>
> Still, it would be good to try CONFIG_PROVE_RCU=y and see what it
> shows you.
>
> Also, I am not seeing similar complaints about 3.10, so it is quite
> possible that a recent change in the ARM-specific idle-loop code is
> doing this to you. It might be well worth looking through recent
> changes in this area, particularly if some older version works well
> for you.
Enabling CONFIG_PROVE_RCU also didn't help.
But we figured out the problem. Thanks for your help. And need your
suggestion in fixing.
if we dump the irq_work_list,
crash> irq_work_list
PER-CPU DATA TYPE:
struct llist_head irq_work_list;
PER-CPU ADDRESSES:
[0]: c53ff90c
[1]: c540d90c
[2]: c541b90c
[3]: c542990c
[4]: c543790c
[5]: c544590c
[6]: c545390c
[7]: c546190c
crash>
crash> list irq_work.llnode -s irq_work.func -h c117f0b4
c117f0b4
func = 0xc0195aa8 <rsp_wakeup>
c117f574
func = 0xc0195aa8 <rsp_wakeup>
crash>
rsp_wakeup is pending in the cpu1's irq_work_list. And cpu1 is already
hot-plugged out.
All the later irq_work_queue calls returns because the work is already pending.
When the issue happens, noticed that a hotplug is happening during
early stages of boot(due to thermal), even before irq_work registers a
cpu_notifer callback. And hence __irq_work_run() will not run as a
part of CPU_DYING notifier.
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/kernel/irq_work.c?id=refs/tags/v3.10.63#n198
and rsp_wakeup is pending from there.
In first approach, we changed the
device_initcall(irq_work_init_cpu_notifier) to earlyinit_initcall and
the issue goes away. Because this makes sure that we have a cpu
notifier before any hotplug happens.
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 55fcce6..5e58767 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -198,6 +198,6 @@ static __init int irq_work_init_cpu_notifier(void)
register_cpu_notifier(&cpu_notify);
return 0;
}
-device_initcall(irq_work_init_cpu_notifier);
+early_initcall(irq_work_init_cpu_notifier);
#endif /* CONFIG_HOTPLUG_CPU */
Another approach is to add syncronize_rcu() in cpu_down path. This
way we makes sure that hotplug waits until a grace period gets over.
This also fixes the problem.
diff --git a/kernel/cpu.c b/kernel/cpu.c
index c56b958..00bdd90 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -311,6 +311,11 @@ static int __ref _cpu_down(unsigned int cpu, int
tasks_frozen)
__func__, cpu);
goto out_release;
}
+#ifdef CONFIG_PREEMPT
+ synchronize_sched();
+#endif
+ synchronize_rcu();
+
smpboot_park_threads(cpu);
err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
Can you please suggest the rite approach?
Thanks,
Arun
>
> Thanx, Paul
>
>> Thanks,
>> Arun
>>
>> >
>> > Thanx, Paul
>> >
>> >> struct rcu_data {
>> >> completed = 5877,
>> >> gpnum = 5877,
>> >> passed_quiesce = true,
>> >> qs_pending = false,
>> >> beenonline = true,
>> >> preemptible = true,
>> >> mynode = 0xc117f340 <rcu_preempt_state>,
>> >> grpmask = 16,
>> >> nxtlist = 0xedaaec00,
>> >> nxttail = {0xc54366c4, 0xe84d350c, 0xe84d350c, 0xe84d350c},
>> >> nxtcompleted = {4294967035, 5878, 5878, 5878},
>> >> qlen_lazy = 105,
>> >> qlen = 415,
>> >> qlen_last_fqs_check = 0,
>> >> n_cbs_invoked = 86323,
>> >> n_nocbs_invoked = 0,
>> >> n_cbs_orphaned = 0,
>> >> n_cbs_adopted = 139,
>> >> n_force_qs_snap = 0,
>> >> blimit = 10,
>> >> dynticks = 0xc5436758,
>> >> dynticks_snap = 7582140,
>> >> dynticks_fqs = 41,
>> >> offline_fqs = 0,
>> >> n_rcu_pending = 59404,
>> >> n_rp_qs_pending = 5,
>> >> n_rp_report_qs = 4633,
>> >> n_rp_cb_ready = 32,
>> >> n_rp_cpu_needs_gp = 41088,
>> >> n_rp_gp_completed = 2844,
>> >> n_rp_gp_started = 1150,
>> >> n_rp_need_nothing = 9657,
>> >> barrier_head = {
>> >> next = 0x0,
>> >> func = 0x0
>> >> },
>> >> oom_head = {
>> >> next = 0x0,
>> >> func = 0x0
>> >> },
>> >> cpu = 4,
>> >> rsp = 0xc117f340 <rcu_preempt_state>
>> >> }
>> >>
>> >>
>> >>
>> >> Also pasting complete rcu_preempt_state.
>> >>
>> >>
>> >>
>> >> rcu_preempt_state = $9 = {
>> >> node = {{
>> >> lock = {
>> >> raw_lock = {
>> >> {
>> >> slock = 3129850509,
>> >> tickets = {
>> >> owner = 47757,
>> >> next = 47757
>> >> }
>> >> }
>> >> },
>> >> magic = 3735899821,
>> >> owner_cpu = 4294967295,
>> >> owner = 0xffffffff
>> >> },
>> >> gpnum = 5877,
>> >> completed = 5877,
>> >> qsmask = 0,
>> >> expmask = 0,
>> >> qsmaskinit = 240,
>> >> grpmask = 0,
>> >> grplo = 0,
>> >> grphi = 7,
>> >> grpnum = 0 '\000',
>> >> level = 0 '\000',
>> >> parent = 0x0,
>> >> blkd_tasks = {
>> >> next = 0xc117f378 <rcu_preempt_state+56>,
>> >> prev = 0xc117f378 <rcu_preempt_state+56>
>> >> },
>> >> gp_tasks = 0x0,
>> >> exp_tasks = 0x0,
>> >> need_future_gp = {1, 0},
>> >> fqslock = {
>> >> raw_lock = {
>> >> {
>> >> slock = 0,
>> >> tickets = {
>> >> owner = 0,
>> >> next = 0
>> >> }
>> >> }
>> >> },
>> >> magic = 3735899821,
>> >> owner_cpu = 4294967295,
>> >> owner = 0xffffffff
>> >> }
>> >> }},
>> >> level = {0xc117f340 <rcu_preempt_state>},
>> >> levelcnt = {1, 0, 0, 0, 0},
>> >> levelspread = "\b",
>> >> rda = 0xc115e6b0 <rcu_preempt_data>,
>> >> call = 0xc01975ac <call_rcu>,
>> >> fqs_state = 0 '\000',
>> >> boost = 0 '\000',
>> >> gpnum = 5877,
>> >> completed = 5877,
>> >> gp_kthread = 0xf0c9e600,
>> >> gp_wq = {
>> >> lock = {
>> >> {
>> >> rlock = {
>> >> raw_lock = {
>> >> {
>> >> slock = 2160230594,
>> >> tickets = {
>> >> owner = 32962,
>> >> next = 32962
>> >> }
>> >> }
>> >> },
>> >> magic = 3735899821,
>> >> owner_cpu = 4294967295,
>> >> owner = 0xffffffff
>> >> }
>> >> }
>> >> },
>> >> task_list = {
>> >> next = 0xf0cd1f20,
>> >> prev = 0xf0cd1f20
>> >> }
>> >> },
>> >> gp_flags = 1,
>> >> orphan_lock = {
>> >> raw_lock = {
>> >> {
>> >> slock = 327685,
>> >> tickets = {
>> >> owner = 5,
>> >> next = 5
>> >> }
>> >> }
>> >> },
>> >> magic = 3735899821,
>> >> owner_cpu = 4294967295,
>> >> owner = 0xffffffff
>> >> },
>> >> orphan_nxtlist = 0x0,
>> >> orphan_nxttail = 0xc117f490 <rcu_preempt_state+336>,
>> >> orphan_donelist = 0x0,
>> >> orphan_donetail = 0xc117f498 <rcu_preempt_state+344>,
>> >> qlen_lazy = 0,
>> >> qlen = 0,
>> >> onoff_mutex = {
>> >> count = {
>> >> counter = 1
>> >> },
>> >> wait_lock = {
>> >> {
>> >> rlock = {
>> >> raw_lock = {
>> >> {
>> >> slock = 811479134,
>> >> tickets = {
>> >> owner = 12382,
>> >> next = 12382
>> >> }
>> >> }
>> >> },
>> >> magic = 3735899821,
>> >> owner_cpu = 4294967295,
>> >> owner = 0xffffffff
>> >> }
>> >> }
>> >> },
>> >> wait_list = {
>> >> next = 0xc117f4bc <rcu_preempt_state+380>,
>> >> prev = 0xc117f4bc <rcu_preempt_state+380>
>> >> },
>> >> owner = 0x0,
>> >> name = 0x0,
>> >> magic = 0xc117f4a8 <rcu_preempt_state+360>
>> >> },
>> >> barrier_mutex = {
>> >> count = {
>> >> counter = 1
>> >> },
>> >> wait_lock = {
>> >> {
>> >> rlock = {
>> >> raw_lock = {
>> >> {
>> >> slock = 0,
>> >> tickets = {
>> >> owner = 0,
>> >> next = 0
>> >> }
>> >> }
>> >> },
>> >> magic = 3735899821,
>> >> owner_cpu = 4294967295,
>> >> owner = 0xffffffff
>> >> }
>> >> }
>> >> },
>> >> wait_list = {
>> >> next = 0xc117f4e4 <rcu_preempt_state+420>,
>> >> prev = 0xc117f4e4 <rcu_preempt_state+420>
>> >> },
>> >> owner = 0x0,
>> >> name = 0x0,
>> >> magic = 0xc117f4d0 <rcu_preempt_state+400>
>> >> },
>> >> barrier_cpu_count = {
>> >> counter = 0
>> >> },
>> >> barrier_completion = {
>> >> done = 0,
>> >> wait = {
>> >> lock = {
>> >> {
>> >> rlock = {
>> >> raw_lock = {
>> >> {
>> >> slock = 0,
>> >> tickets = {
>> >> owner = 0,
>> >> next = 0
>> >> }
>> >> }
>> >> },
>> >> magic = 0,
>> >> owner_cpu = 0,
>> >> owner = 0x0
>> >> }
>> >> }
>> >> },
>> >> task_list = {
>> >> next = 0x0,
>> >> prev = 0x0
>> >> }
>> >> }
>> >> },
>> >> n_barrier_done = 0,
>> >> expedited_start = {
>> >> counter = 0
>> >> },
>> >> expedited_done = {
>> >> counter = 0
>> >> },
>> >> expedited_wrap = {
>> >> counter = 0
>> >> },
>> >> expedited_tryfail = {
>> >> counter = 0
>> >> },
>> >> expedited_workdone1 = {
>> >> counter = 0
>> >> },
>> >> expedited_workdone2 = {
>> >> counter = 0
>> >> },
>> >> expedited_normal = {
>> >> counter = 0
>> >> },
>> >> expedited_stoppedcpus = {
>> >> counter = 0
>> >> },
>> >> expedited_done_tries = {
>> >> counter = 0
>> >> },
>> >> expedited_done_lost = {
>> >> counter = 0
>> >> },
>> >> expedited_done_exit = {
>> >> counter = 0
>> >> },
>> >> jiffies_force_qs = 4294963917,
>> >> n_force_qs = 4028,
>> >> n_force_qs_lh = 0,
>> >> n_force_qs_ngp = 0,
>> >> gp_start = 4294963911,
>> >> jiffies_stall = 4294966011,
>> >> gp_max = 17,
>> >> name = 0xc0d833ab "rcu_preempt",
>> >> abbr = 112 'p',
>> >> flavors = {
>> >> next = 0xc117f2ec <rcu_bh_state+556>,
>> >> prev = 0xc117f300 <rcu_struct_flavors>
>> >> },
>> >> wakeup_work = {
>> >> flags = 3,
>> >> llnode = {
>> >> next = 0x0
>> >> },
>> >> func = 0xc0195aa8 <rsp_wakeup>
>> >> }
>> >> }
>> >>
>> >> Hope this helps.
>> >>
>> >> Thanks,
>> >> Arun
>> >>
>> >>
>> >> On Tue, Dec 16, 2014 at 11:59 AM, Arun KS <arunks.linux@...il.com> wrote:
>> >> > Hello,
>> >> >
>> >> > I dig little deeper to understand the situation.
>> >> > All other cpus are in idle thread already.
>> >> > As per my understanding, for the grace period to end, at-least one of
>> >> > the following should happen on all online cpus,
>> >> >
>> >> > 1. a context switch.
>> >> > 2. user space switch.
>> >> > 3. switch to idle thread.
>> >> >
>> >> > In this situation, since all the other cores are already in idle, non
>> >> > of the above are meet on all online cores.
>> >> > So grace period is getting extended and never finishes. Below is the
>> >> > state of runqueue when the hang happens.
>> >> > --------------start------------------------------------
>> >> > crash> runq
>> >> > CPU 0 [OFFLINE]
>> >> >
>> >> > CPU 1 [OFFLINE]
>> >> >
>> >> > CPU 2 [OFFLINE]
>> >> >
>> >> > CPU 3 [OFFLINE]
>> >> >
>> >> > CPU 4 RUNQUEUE: c3192e40
>> >> > CURRENT: PID: 0 TASK: f0874440 COMMAND: "swapper/4"
>> >> > RT PRIO_ARRAY: c3192f20
>> >> > [no tasks queued]
>> >> > CFS RB_ROOT: c3192eb0
>> >> > [no tasks queued]
>> >> >
>> >> > CPU 5 RUNQUEUE: c31a0e40
>> >> > CURRENT: PID: 0 TASK: f0874980 COMMAND: "swapper/5"
>> >> > RT PRIO_ARRAY: c31a0f20
>> >> > [no tasks queued]
>> >> > CFS RB_ROOT: c31a0eb0
>> >> > [no tasks queued]
>> >> >
>> >> > CPU 6 RUNQUEUE: c31aee40
>> >> > CURRENT: PID: 0 TASK: f0874ec0 COMMAND: "swapper/6"
>> >> > RT PRIO_ARRAY: c31aef20
>> >> > [no tasks queued]
>> >> > CFS RB_ROOT: c31aeeb0
>> >> > [no tasks queued]
>> >> >
>> >> > CPU 7 RUNQUEUE: c31bce40
>> >> > CURRENT: PID: 0 TASK: f0875400 COMMAND: "swapper/7"
>> >> > RT PRIO_ARRAY: c31bcf20
>> >> > [no tasks queued]
>> >> > CFS RB_ROOT: c31bceb0
>> >> > [no tasks queued]
>> >> > --------------end------------------------------------
>> >> >
>> >> > If my understanding is correct the below patch should help, because it
>> >> > will expedite grace periods during suspend,
>> >> > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=d1d74d14e98a6be740a6f12456c7d9ad47be9c9c
>> >> >
>> >> > But I wonder why it was not taken to stable trees. Can we take it?
>> >> > Appreciate your help.
>> >> >
>> >> > Thanks,
>> >> > Arun
>> >> >
>> >> > On Mon, Dec 15, 2014 at 10:34 PM, Arun KS <arunks.linux@...il.com> wrote:
>> >> >> Hi,
>> >> >>
>> >> >> Here is the backtrace of the process hanging in wait_rcu_gp,
>> >> >>
>> >> >> PID: 247 TASK: e16e7380 CPU: 4 COMMAND: "kworker/u16:5"
>> >> >> #0 [<c09fead0>] (__schedule) from [<c09fcab0>]
>> >> >> #1 [<c09fcab0>] (schedule_timeout) from [<c09fe050>]
>> >> >> #2 [<c09fe050>] (wait_for_common) from [<c013b2b4>]
>> >> >> #3 [<c013b2b4>] (wait_rcu_gp) from [<c0142f50>]
>> >> >> #4 [<c0142f50>] (atomic_notifier_chain_unregister) from [<c06b2ab8>]
>> >> >> #5 [<c06b2ab8>] (cpufreq_interactive_disable_sched_input) from [<c06b32a8>]
>> >> >> #6 [<c06b32a8>] (cpufreq_governor_interactive) from [<c06abbf8>]
>> >> >> #7 [<c06abbf8>] (__cpufreq_governor) from [<c06ae474>]
>> >> >> #8 [<c06ae474>] (__cpufreq_remove_dev_finish) from [<c06ae8c0>]
>> >> >> #9 [<c06ae8c0>] (cpufreq_cpu_callback) from [<c0a0185c>]
>> >> >> #10 [<c0a0185c>] (notifier_call_chain) from [<c0121888>]
>> >> >> #11 [<c0121888>] (__cpu_notify) from [<c0121a04>]
>> >> >> #12 [<c0121a04>] (cpu_notify_nofail) from [<c09ee7f0>]
>> >> >> #13 [<c09ee7f0>] (_cpu_down) from [<c0121b70>]
>> >> >> #14 [<c0121b70>] (disable_nonboot_cpus) from [<c016788c>]
>> >> >> #15 [<c016788c>] (suspend_devices_and_enter) from [<c0167bcc>]
>> >> >> #16 [<c0167bcc>] (pm_suspend) from [<c0167d94>]
>> >> >> #17 [<c0167d94>] (try_to_suspend) from [<c0138460>]
>> >> >> #18 [<c0138460>] (process_one_work) from [<c0138b18>]
>> >> >> #19 [<c0138b18>] (worker_thread) from [<c013dc58>]
>> >> >> #20 [<c013dc58>] (kthread) from [<c01061b8>]
>> >> >>
>> >> >> Will this patch helps here,
>> >> >> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=d1d74d14e98a6be740a6f12456c7d9ad47be9c9c
>> >> >>
>> >> >> I couldn't really understand why it got struck in synchronize_rcu().
>> >> >> Please give some pointers to debug this further.
>> >> >>
>> >> >> Below are the configs enable related to RCU.
>> >> >>
>> >> >> CONFIG_TREE_PREEMPT_RCU=y
>> >> >> CONFIG_PREEMPT_RCU=y
>> >> >> CONFIG_RCU_STALL_COMMON=y
>> >> >> CONFIG_RCU_FANOUT=32
>> >> >> CONFIG_RCU_FANOUT_LEAF=16
>> >> >> CONFIG_RCU_FAST_NO_HZ=y
>> >> >> CONFIG_RCU_CPU_STALL_TIMEOUT=21
>> >> >> CONFIG_RCU_CPU_STALL_VERBOSE=y
>> >> >>
>> >> >> Kernel version is 3.10.28
>> >> >> Architecture is ARM
>> >> >>
>> >> >> Thanks,
>> >> >> Arun
>> >>
>> >
>
>> crash> struct rcu_data C54286B0
>> struct rcu_data {
>> completed = 2833,
>> gpnum = 2833,
>> passed_quiesce = false,
>> qs_pending = false,
>> beenonline = true,
>> preemptible = true,
>> mynode = 0xc117f340 <rcu_preempt_state>,
>> grpmask = 8,
>> nxtlist = 0x0,
>> nxttail = {0xc54286c4, 0xc54286c4, 0xc54286c4, 0x0},
>> nxtcompleted = {0, 4294967136, 4294967137, 4294967137},
>> qlen_lazy = 0,
>> qlen = 0,
>> qlen_last_fqs_check = 0,
>> n_cbs_invoked = 609,
>> n_nocbs_invoked = 0,
>> n_cbs_orphaned = 13,
>> n_cbs_adopted = 0,
>> n_force_qs_snap = 1428,
>> blimit = 10,
>> dynticks = 0xc5428758,
>> dynticks_snap = 13206053,
>> dynticks_fqs = 16,
>> offline_fqs = 0,
>> n_rcu_pending = 181,
>> n_rp_qs_pending = 1,
>> n_rp_report_qs = 21,
>> n_rp_cb_ready = 0,
>> n_rp_cpu_needs_gp = 0,
>> n_rp_gp_completed = 22,
>> n_rp_gp_started = 8,
>> n_rp_need_nothing = 130,
>> barrier_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> oom_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> cpu = 3,
>> rsp = 0xc117f340 <rcu_preempt_state>
>> }
>>
>> crash> struct rcu_data C541A6B0
>> struct rcu_data {
>> completed = 5877,
>> gpnum = 5877,
>> passed_quiesce = true,
>> qs_pending = false,
>> beenonline = true,
>> preemptible = true,
>> mynode = 0xc117f340 <rcu_preempt_state>,
>> grpmask = 4,
>> nxtlist = 0x0,
>> nxttail = {0xc541a6c4, 0xc541a6c4, 0xc541a6c4, 0x0},
>> nxtcompleted = {0, 5877, 5878, 5878},
>> qlen_lazy = 0,
>> qlen = 0,
>> qlen_last_fqs_check = 0,
>> n_cbs_invoked = 61565,
>> n_nocbs_invoked = 0,
>> n_cbs_orphaned = 139,
>> n_cbs_adopted = 100,
>> n_force_qs_snap = 0,
>> blimit = 10,
>> dynticks = 0xc541a758,
>> dynticks_snap = 13901017,
>> dynticks_fqs = 75,
>> offline_fqs = 0,
>> n_rcu_pending = 16546,
>> n_rp_qs_pending = 3,
>> n_rp_report_qs = 4539,
>> n_rp_cb_ready = 69,
>> n_rp_cpu_needs_gp = 782,
>> n_rp_gp_completed = 4196,
>> n_rp_gp_started = 1739,
>> n_rp_need_nothing = 5221,
>> barrier_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> oom_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> cpu = 2,
>> rsp = 0xc117f340 <rcu_preempt_state>
>> }
>>
>> crash> struct rcu_data C540C6B0
>> struct rcu_data {
>> completed = 5877,
>> gpnum = 5877,
>> passed_quiesce = true,
>> qs_pending = false,
>> beenonline = true,
>> preemptible = true,
>> mynode = 0xc117f340 <rcu_preempt_state>,
>> grpmask = 2,
>> nxtlist = 0x0,
>> nxttail = {0xc540c6c4, 0xc540c6c4, 0xc540c6c4, 0x0},
>> nxtcompleted = {4294967030, 5878, 5878, 5878},
>> qlen_lazy = 0,
>> qlen = 0,
>> qlen_last_fqs_check = 0,
>> n_cbs_invoked = 74292,
>> n_nocbs_invoked = 0,
>> n_cbs_orphaned = 100,
>> n_cbs_adopted = 65,
>> n_force_qs_snap = 0,
>> blimit = 10,
>> dynticks = 0xc540c758,
>> dynticks_snap = 10753433,
>> dynticks_fqs = 69,
>> offline_fqs = 0,
>> n_rcu_pending = 18350,
>> n_rp_qs_pending = 6,
>> n_rp_report_qs = 5009,
>> n_rp_cb_ready = 50,
>> n_rp_cpu_needs_gp = 915,
>> n_rp_gp_completed = 4423,
>> n_rp_gp_started = 1826,
>> n_rp_need_nothing = 6127,
>> barrier_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> oom_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> cpu = 1,
>> rsp = 0xc117f340 <rcu_preempt_state>
>> }
>> crash> struct rcu_data C53FE6B0
>> struct rcu_data {
>> completed = 5877,
>> gpnum = 5877,
>> passed_quiesce = true,
>> qs_pending = false,
>> beenonline = true,
>> preemptible = true,
>> mynode = 0xc117f340 <rcu_preempt_state>,
>> grpmask = 1,
>> nxtlist = 0x0,
>> nxttail = {0xc53fe6c4, 0xc53fe6c4, 0xc53fe6c4, 0x0},
>> nxtcompleted = {4294966997, 5875, 5876, 5876},
>> qlen_lazy = 0,
>> qlen = 0,
>> qlen_last_fqs_check = 0,
>> n_cbs_invoked = 123175,
>> n_nocbs_invoked = 0,
>> n_cbs_orphaned = 52,
>> n_cbs_adopted = 0,
>> n_force_qs_snap = 0,
>> blimit = 10,
>> dynticks = 0xc53fe758,
>> dynticks_snap = 6330446,
>> dynticks_fqs = 46,
>> offline_fqs = 0,
>> n_rcu_pending = 22529,
>> n_rp_qs_pending = 3,
>> n_rp_report_qs = 5290,
>> n_rp_cb_ready = 279,
>> n_rp_cpu_needs_gp = 740,
>> n_rp_gp_completed = 2707,
>> n_rp_gp_started = 1208,
>> n_rp_need_nothing = 12305,
>> barrier_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> oom_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> cpu = 0,
>> rsp = 0xc117f340 <rcu_preempt_state>
>> }
>>
>
>> crash> struct rcu_data c54366b0
>> struct rcu_data {
>> completed = 5877,
>> gpnum = 5877,
>> passed_quiesce = true,
>> qs_pending = false,
>> beenonline = true,
>> preemptible = true,
>> mynode = 0xc117f340 <rcu_preempt_state>,
>> grpmask = 16,
>> nxtlist = 0xedaaec00,
>> nxttail = {0xc54366c4, 0xe84d350c, 0xe84d350c, 0xe84d350c},
>> nxtcompleted = {4294967035, 5878, 5878, 5878},
>> qlen_lazy = 105,
>> qlen = 415,
>> qlen_last_fqs_check = 0,
>> n_cbs_invoked = 86323,
>> n_nocbs_invoked = 0,
>> n_cbs_orphaned = 0,
>> n_cbs_adopted = 139,
>> n_force_qs_snap = 0,
>> blimit = 10,
>> dynticks = 0xc5436758,
>> dynticks_snap = 7582140,
>> dynticks_fqs = 41,
>> offline_fqs = 0,
>> n_rcu_pending = 59404,
>> n_rp_qs_pending = 5,
>> n_rp_report_qs = 4633,
>> n_rp_cb_ready = 32,
>> n_rp_cpu_needs_gp = 41088,
>> n_rp_gp_completed = 2844,
>> n_rp_gp_started = 1150,
>> n_rp_need_nothing = 9657,
>> barrier_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> oom_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> cpu = 4,
>> rsp = 0xc117f340 <rcu_preempt_state>
>> }
>>
>> crash> struct rcu_data c54446b0
>> struct rcu_data {
>> completed = 5877,
>> gpnum = 5877,
>> passed_quiesce = true,
>> qs_pending = false,
>> beenonline = true,
>> preemptible = true,
>> mynode = 0xc117f340 <rcu_preempt_state>,
>> grpmask = 32,
>> nxtlist = 0xcf9e856c,
>> nxttail = {0xc54446c4, 0xcfb3050c, 0xcfb3050c, 0xcfb3050c},
>> nxtcompleted = {0, 5878, 5878, 5878},
>> qlen_lazy = 0,
>> qlen = 117,
>> qlen_last_fqs_check = 0,
>> n_cbs_invoked = 36951,
>> n_nocbs_invoked = 0,
>> n_cbs_orphaned = 0,
>> n_cbs_adopted = 0,
>> n_force_qs_snap = 1428,
>> blimit = 10,
>> dynticks = 0xc5444758,
>> dynticks_snap = 86034,
>> dynticks_fqs = 46,
>> offline_fqs = 0,
>> n_rcu_pending = 49104,
>> n_rp_qs_pending = 3,
>> n_rp_report_qs = 2360,
>> n_rp_cb_ready = 18,
>> n_rp_cpu_needs_gp = 40106,
>> n_rp_gp_completed = 1334,
>> n_rp_gp_started = 791,
>> n_rp_need_nothing = 4495,
>> barrier_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> oom_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> cpu = 5,
>> rsp = 0xc117f340 <rcu_preempt_state>
>> }
>>
>> crash> struct rcu_data c54526b0
>> struct rcu_data {
>> completed = 5877,
>> gpnum = 5877,
>> passed_quiesce = true,
>> qs_pending = false,
>> beenonline = true,
>> preemptible = true,
>> mynode = 0xc117f340 <rcu_preempt_state>,
>> grpmask = 64,
>> nxtlist = 0xe613d200,
>> nxttail = {0xc54526c4, 0xe6fc9d0c, 0xe6fc9d0c, 0xe6fc9d0c},
>> nxtcompleted = {0, 5878, 5878, 5878},
>> qlen_lazy = 2,
>> qlen = 35,
>> qlen_last_fqs_check = 0,
>> n_cbs_invoked = 34459,
>> n_nocbs_invoked = 0,
>> n_cbs_orphaned = 0,
>> n_cbs_adopted = 0,
>> n_force_qs_snap = 1428,
>> blimit = 10,
>> dynticks = 0xc5452758,
>> dynticks_snap = 116840,
>> dynticks_fqs = 47,
>> offline_fqs = 0,
>> n_rcu_pending = 48486,
>> n_rp_qs_pending = 3,
>> n_rp_report_qs = 2223,
>> n_rp_cb_ready = 24,
>> n_rp_cpu_needs_gp = 40101,
>> n_rp_gp_completed = 1226,
>> n_rp_gp_started = 789,
>> n_rp_need_nothing = 4123,
>> barrier_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> oom_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> cpu = 6,
>> rsp = 0xc117f340 <rcu_preempt_state>
>> }
>>
>> crash> struct rcu_data c54606b0
>> struct rcu_data {
>> completed = 5877,
>> gpnum = 5877,
>> passed_quiesce = true,
>> qs_pending = false,
>> beenonline = true,
>> preemptible = true,
>> mynode = 0xc117f340 <rcu_preempt_state>,
>> grpmask = 128,
>> nxtlist = 0xdec32a6c,
>> nxttail = {0xc54606c4, 0xe6fcf10c, 0xe6fcf10c, 0xe6fcf10c},
>> nxtcompleted = {0, 5878, 5878, 5878},
>> qlen_lazy = 1,
>> qlen = 30,
>> qlen_last_fqs_check = 0,
>> n_cbs_invoked = 31998,
>> n_nocbs_invoked = 0,
>> n_cbs_orphaned = 0,
>> n_cbs_adopted = 0,
>> n_force_qs_snap = 1428,
>> blimit = 10,
>> dynticks = 0xc5460758,
>> dynticks_snap = 57846,
>> dynticks_fqs = 54,
>> offline_fqs = 0,
>> n_rcu_pending = 47502,
>> n_rp_qs_pending = 2,
>> n_rp_report_qs = 2142,
>> n_rp_cb_ready = 37,
>> n_rp_cpu_needs_gp = 40049,
>> n_rp_gp_completed = 1223,
>> n_rp_gp_started = 661,
>> n_rp_need_nothing = 3390,
>> barrier_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> oom_head = {
>> next = 0x0,
>> func = 0x0
>> },
>> cpu = 7,
>> rsp = 0xc117f340 <rcu_preempt_state>
>> }
>
>>
>> rcu_preempt_state = $9 = {
>> node = {{
>> lock = {
>> raw_lock = {
>> {
>> slock = 3129850509,
>> tickets = {
>> owner = 47757,
>> next = 47757
>> }
>> }
>> },
>> magic = 3735899821,
>> owner_cpu = 4294967295,
>> owner = 0xffffffff
>> },
>> gpnum = 5877,
>> completed = 5877,
>> qsmask = 0,
>> expmask = 0,
>> qsmaskinit = 240,
>> grpmask = 0,
>> grplo = 0,
>> grphi = 7,
>> grpnum = 0 '\000',
>> level = 0 '\000',
>> parent = 0x0,
>> blkd_tasks = {
>> next = 0xc117f378 <rcu_preempt_state+56>,
>> prev = 0xc117f378 <rcu_preempt_state+56>
>> },
>> gp_tasks = 0x0,
>> exp_tasks = 0x0,
>> need_future_gp = {1, 0},
>> fqslock = {
>> raw_lock = {
>> {
>> slock = 0,
>> tickets = {
>> owner = 0,
>> next = 0
>> }
>> }
>> },
>> magic = 3735899821,
>> owner_cpu = 4294967295,
>> owner = 0xffffffff
>> }
>> }},
>> level = {0xc117f340 <rcu_preempt_state>},
>> levelcnt = {1, 0, 0, 0, 0},
>> levelspread = "\b",
>> rda = 0xc115e6b0 <rcu_preempt_data>,
>> call = 0xc01975ac <call_rcu>,
>> fqs_state = 0 '\000',
>> boost = 0 '\000',
>> gpnum = 5877,
>> completed = 5877,
>> gp_kthread = 0xf0c9e600,
>> gp_wq = {
>> lock = {
>> {
>> rlock = {
>> raw_lock = {
>> {
>> slock = 2160230594,
>> tickets = {
>> owner = 32962,
>> next = 32962
>> }
>> }
>> },
>> magic = 3735899821,
>> owner_cpu = 4294967295,
>> owner = 0xffffffff
>> }
>> }
>> },
>> task_list = {
>> next = 0xf0cd1f20,
>> prev = 0xf0cd1f20
>> }
>> },
>> gp_flags = 1,
>> orphan_lock = {
>> raw_lock = {
>> {
>> slock = 327685,
>> tickets = {
>> owner = 5,
>> next = 5
>> }
>> }
>> },
>> magic = 3735899821,
>> owner_cpu = 4294967295,
>> owner = 0xffffffff
>> },
>> orphan_nxtlist = 0x0,
>> orphan_nxttail = 0xc117f490 <rcu_preempt_state+336>,
>> orphan_donelist = 0x0,
>> orphan_donetail = 0xc117f498 <rcu_preempt_state+344>,
>> qlen_lazy = 0,
>> qlen = 0,
>> onoff_mutex = {
>> count = {
>> counter = 1
>> },
>> wait_lock = {
>> {
>> rlock = {
>> raw_lock = {
>> {
>> slock = 811479134,
>> tickets = {
>> owner = 12382,
>> next = 12382
>> }
>> }
>> },
>> magic = 3735899821,
>> owner_cpu = 4294967295,
>> owner = 0xffffffff
>> }
>> }
>> },
>> wait_list = {
>> next = 0xc117f4bc <rcu_preempt_state+380>,
>> prev = 0xc117f4bc <rcu_preempt_state+380>
>> },
>> owner = 0x0,
>> name = 0x0,
>> magic = 0xc117f4a8 <rcu_preempt_state+360>
>> },
>> barrier_mutex = {
>> count = {
>> counter = 1
>> },
>> wait_lock = {
>> {
>> rlock = {
>> raw_lock = {
>> {
>> slock = 0,
>> tickets = {
>> owner = 0,
>> next = 0
>> }
>> }
>> },
>> magic = 3735899821,
>> owner_cpu = 4294967295,
>> owner = 0xffffffff
>> }
>> }
>> },
>> wait_list = {
>> next = 0xc117f4e4 <rcu_preempt_state+420>,
>> prev = 0xc117f4e4 <rcu_preempt_state+420>
>> },
>> owner = 0x0,
>> name = 0x0,
>> magic = 0xc117f4d0 <rcu_preempt_state+400>
>> },
>> barrier_cpu_count = {
>> counter = 0
>> },
>> barrier_completion = {
>> done = 0,
>> wait = {
>> lock = {
>> {
>> rlock = {
>> raw_lock = {
>> {
>> slock = 0,
>> tickets = {
>> owner = 0,
>> next = 0
>> }
>> }
>> },
>> magic = 0,
>> owner_cpu = 0,
>> owner = 0x0
>> }
>> }
>> },
>> task_list = {
>> next = 0x0,
>> prev = 0x0
>> }
>> }
>> },
>> n_barrier_done = 0,
>> expedited_start = {
>> counter = 0
>> },
>> expedited_done = {
>> counter = 0
>> },
>> expedited_wrap = {
>> counter = 0
>> },
>> expedited_tryfail = {
>> counter = 0
>> },
>> expedited_workdone1 = {
>> counter = 0
>> },
>> expedited_workdone2 = {
>> counter = 0
>> },
>> expedited_normal = {
>> counter = 0
>> },
>> expedited_stoppedcpus = {
>> counter = 0
>> },
>> expedited_done_tries = {
>> counter = 0
>> },
>> expedited_done_lost = {
>> counter = 0
>> },
>> expedited_done_exit = {
>> counter = 0
>> },
>> jiffies_force_qs = 4294963917,
>> n_force_qs = 4028,
>> n_force_qs_lh = 0,
>> n_force_qs_ngp = 0,
>> gp_start = 4294963911,
>> jiffies_stall = 4294966011,
>> gp_max = 17,
>> name = 0xc0d833ab "rcu_preempt",
>> abbr = 112 'p',
>> flavors = {
>> next = 0xc117f2ec <rcu_bh_state+556>,
>> prev = 0xc117f300 <rcu_struct_flavors>
>> },
>> wakeup_work = {
>> flags = 3,
>> llnode = {
>> next = 0x0
>> },
>> func = 0xc0195aa8 <rsp_wakeup>
>> }
>>
>>
>
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