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Date: Sat, 6 Aug 2022 15:19:37 +0800
From: "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To: <paulmck@...nel.org>
CC: Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>,
"Mel Gorman" <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>,
<linux-kernel@...r.kernel.org>,
Frederic Weisbecker <frederic@...nel.org>,
Neeraj Upadhyay <quic_neeraju@...cinc.com>,
Josh Triplett <josh@...htriplett.org>,
"Mathieu Desnoyers" <mathieu.desnoyers@...icios.com>,
Lai Jiangshan <jiangshanlai@...il.com>,
Joel Fernandes <joel@...lfernandes.org>, <rcu@...r.kernel.org>
Subject: Re: [PATCH v4 0/2] rcu: Display registers of self-detected stall as
far as possible
On 2022/8/5 16:09, Leizhen (ThunderTown) wrote:
>
>
> On 2022/8/5 2:09, Paul E. McKenney wrote:
>> On Thu, Aug 04, 2022 at 10:34:18AM +0800, Zhen Lei wrote:
>>> v3 --> v4:
>>> 1. To avoid undo/redo, merge patch 1-2 in v3 into one.
>>>
>>> v2 --> v3:
>>> 1. Patch 1 Add trigger_single_cpu_backtrace(cpu) in synchronize_rcu_expedited_wait()
>>> Subsequently, we can see that all callers of dump_cpu_task() try
>>> trigger_single_cpu_backtrace() first. Then I do the cleanup in Patch 2.
>>> 2. Patch 3, as Paul E. McKenney's suggestion, push the code into dump_cpu_task().
>>>
>>> For newcomers:
>>> Currently, dump_cpu_task() is mainly used by RCU, in order to dump the
>>> stack traces of the current task of the specified CPU when a rcu stall
>>> is detected.
>>>
>>> For architectures that do not support NMI interrupts, registers is not
>>> printed when rcu stall is self-detected. This patch series improve it.
>>
>> Thank you! I have queued both for further testing and review. I had
>> to rebase them to the -rcu tree's "dev" branch. There was one trivial
>> conflict, but could you please check the resulting commits, both for
>> my wordsmithing and to make sure that your changes still work in your
>> environment? (I do not have access to that sort of hardware.)
I tested it on x86, arm64, and arm32 platforms, and all the results are
as expected.
x86:
[ 54.750801] rcu: INFO: rcu_preempt self-detected stall on CPU
[ 54.754289] rcu: 0-....: (4998 ticks this GP) idle=9e5c/1/0x4000000000000000 softirq=855/855 fqs=1219
[ 54.755307] (t=5005 jiffies g=1 q=36 ncpus=8)
[ 54.755311] CPU: 0 PID: 379 Comm: test0 Not tainted 5.19.0-rc3-00108-g0aa4c0b532b6 #1
[ 54.755313] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
[ 54.755321] RIP: 0010:pvclock_clocksource_read+0x12/0xc0
[ 54.755328] Code: b6 47 1d 8b 17 39 ca 75 f1 22 05 79 9e a3 01 c3 0f 1f 84 00 00 00 00 00 55 53 48 83 ec 08 8b 17 89 d6 83 e6 fe 0f ae e8 0f 31 <48> c1 e2 20 48 8b 5f 10 0f b6 6f 1d 48 09 c2 48 89 d0 0f be 57 1c
[ 54.755330] RSP: 0018:ffff936040547eb0 EFLAGS: 00000206
[ 54.755332] RAX: 0000000088921016 RBX: 0000000c9957cfbb RCX: 0000000000000000
[ 54.755333] RDX: 0000000000000026 RSI: 0000000000000006 RDI: ffffffffa46de000
[ 54.755335] RBP: 0000000000000000 R08: 0000001336358637 R09: ffff936040547ea0
[ 54.755336] R10: ffffffffa3e55dc0 R11: ffffffffa46ee4a1 R12: 0000000000003e42
[ 54.755338] R13: ffffffffa4727d40 R14: ffffffffa28b0270 R15: 0000000000000000
[ 54.755339] FS: 0000000000000000(0000) GS:ffff8e0cefc00000(0000) knlGS:0000000000000000
[ 54.755343] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 54.755344] CR2: 0000563a3b1bae40 CR3: 0000000104378000 CR4: 00000000000006f0
[ 54.755345] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 54.755346] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 54.755347] Call Trace:
[ 54.755356] <TASK>
[ 54.755358] kvm_clock_read+0x14/0x30
[ 54.755361] ktime_get+0x39/0x90
[ 54.755368] test_task+0x3f/0x60
[ 54.755373] kthread+0xe3/0x110
[ 54.755376] ? kthread_complete_and_exit+0x20/0x20
[ 54.755378] ret_from_fork+0x22/0x30
[ 54.755385] </TASK>
arm64:
[ 27.235111] rcu: INFO: rcu_preempt self-detected stall on CPU
[ 27.236915] rcu: 0-....: (1249 ticks this GP) idle=cac4/1/0x4000000000000000 softirq=1434/1434 fqs=625
[ 27.237475] (t=1251 jiffies g=3421 q=18 ncpus=4)
[ 27.238994] CPU: 0 PID: 356 Comm: test0 Not tainted 5.19.0-rc3-00107-gbf5cb0bc4689 #1
[ 27.239467] Hardware name: linux,dummy-virt (DT)
[ 27.240038] pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 27.240358] pc : arch_counter_read+0x18/0x24
[ 27.241439] lr : arch_counter_read+0x18/0x24
[ 27.241645] sp : ffff800008e53df0
[ 27.241786] x29: ffff800008e53df0 x28: 0000000000000000 x27: 0000000000000000
[ 27.242256] x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
[ 27.242586] x23: 0000000000001f40 x22: ffffd62939e61df0 x21: 00000006556b8c60
[ 27.243115] x20: 00000000000028ae x19: ffffd6293aad7300 x18: ffffffffffffffff
[ 27.243396] x17: 0000000000000001 x16: 0000000000000000 x15: ffffd6293aabad8e
[ 27.243671] x14: ffffffffffffffff x13: ffffd6293aabad85 x12: fffffffffffc4627
[ 27.243947] x11: ffffd6293a772c98 x10: 0000000000000a60 x9 : 0000000000000fa0
[ 27.244256] x8 : ffffd6293a772c50 x7 : ffff800008e53c40 x6 : 00000000767b62ab
[ 27.244541] x5 : 01ffffffffffffff x4 : 0000000000000000 x3 : 0000000000000017
[ 27.244813] x2 : 00000000000028ae x1 : ffff800008e53df0 x0 : 0000000076804ac1
[ 27.245247] Call trace:
[ 27.245457] arch_counter_read+0x18/0x24
[ 27.245845] ktime_get+0x48/0xa0
[ 27.246012] test_task+0x6c/0xec
[ 27.246151] kthread+0x10c/0x110
[ 27.246282] ret_from_fork+0x10/0x20
arm32
rcu: INFO: rcu_sched self-detected stall on CPU
rcu: 0-....: (499 ticks this GP) idle=c734/1/0x40000002 softirq=161/161 fqs=249
(t=500 jiffies g=-899 q=16 ncpus=4)
CPU: 0 PID: 70 Comm: test0 Not tainted 5.19.0-rc3+ #1
Hardware name: ARM-Versatile Express
PC is at ktime_get+0x4c/0xe8
LR is at ktime_get+0x4c/0xe8
pc : [<8019b4fc>] lr : [<8019b4fc>] psr: 60000013
sp : c8a71f28 ip : 00000001 fp : 00000001
r10: f8ecbe00 r9 : 431bde82 r8 : d7b634db
r7 : 00000a0a r6 : e2be6498 r5 : 00000001 r4 : 80ca8700
r3 : ffffffff r2 : ff3a2de2 r1 : 00000000 r0 : 00c5d21d
Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
Control: 10c5387d Table: 627f806a DAC: 00000051
ktime_get from test_task+0x44/0x110
test_task from kthread+0xd8/0xf4
kthread from ret_from_fork+0x14/0x2c
Exception stack(0xc8a71fb0 to 0xc8a71ff8)
1fa0: 00000000 00000000 00000000 00000000
1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
1fe0: 00000000 00000000 00000000 00000000 00000013 00000000
>
> Your description is much clearer than mine, thanks. I will test it
> tomorrow, the international network speed is too slow during the day.
>
>>
>> In the future, could you please send your patches against the -rcu
>> tree's "dev" branch?
>
> Okay, no problem. I'll do it next time.
>
>>
>> Thanx, Paul
>>
>>> v2:
>>> https://lkml.org/lkml/2022/7/27/1800
>>>
>>> Zhen Lei (2):
>>> sched/debug: Try trigger_single_cpu_backtrace(cpu) in dump_cpu_task()
>>> sched/debug: Show the registers of 'current' in dump_cpu_task()
>>>
>>> kernel/rcu/tree_stall.h | 8 +++-----
>>> kernel/sched/core.c | 14 ++++++++++++++
>>> kernel/smp.c | 3 +--
>>> 3 files changed, 18 insertions(+), 7 deletions(-)
>>>
>>> --
>>> 2.25.1
>>>
>> .
>>
>
--
Regards,
Zhen Lei
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